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What You Should Know for the 2015-2016 Influenza Season

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Note: The Advisory Committee on Immunization Practices (ACIP) 2015-16 Recommendations for prevention and control of seasonal influenza were published in complete form in the Morbidity and Mortality Weekly Report on August 6, 2015. The report is available at MMWR.

Visit What You Should Know for the 2016-2017 Influenza Season for flu and flu vaccine information specific to the current flu season.

What sort of flu season are we experiencing?

Flu seasons can vary in their timing, severity, and duration from one season to another.

This flu season started a little later than it has during the previous three flu seasons. The season also peaked later than usual and activity has remained elevated later also. While H3N2 viruses predominated early in the season, H1N1 viruses have been the most common in recent weeks and are now the predominant virus for this season. This is the virus that emerged in 2009 to cause a pandemic. In the past, H1N1 flu viruses have caused severe illness in some children & young-and middle-aged adults. While there have been reports of severe flu illnesses and deaths this season, overall this season has been milder than the previous three seasons and severity indicators have not been excessively high.

Have new flu viruses circulated this season?

The majority of influenza viruses analyzed this season have been like the vaccine viruses. For more information about how flu viruses change, visit How the Flu Virus Can Change.

Is the United States having a flu epidemic?

The United States experiences epidemics of seasonal flu each year. This time of year is called "flu season." In the United States, flu season occurs in the winter; flu outbreaks can happen as early as October and can last as late as May. CDC says the flu season begins when certain key flu indicators (for example, levels of influenza-like illness (ILI), hospitalization and deaths) rise and remain elevated for a number of consecutive weeks. Usually ILI increases first, followed by an increase in hospitalizations, which is then followed by increases in flu-associated deaths.

For the most current influenza surveillance information, please see FluView at http://www.cdc.gov/flu/weekly/

When did flu activity begin? When will it peak?

The timing of flu is unpredictable and can vary in different parts of the country and from season to season. Most seasonal flu activity typically occurs between October and May. Flu activity most commonly peaks in the United States between December and February.

Influenza activity in the United States during the 2015-2016 season began to increase in late December 2015 and continued to increase slowly through early March 2016. The peak week of flu activity for the 2015-2016 season was week 10 ending March 12, 2016.  This would be one of the later season peaks on record. Over the last 18 seasons (including this season), only three seasons have peaked in March (2015-2016, 2011-2012 and 2005-2006). No season has peaked later than March.

What should I do to protect myself from flu this season?

CDC recommends a yearly flu vaccine for everyone 6 months of age and older as the first and most important step in protecting against this serious disease. People should begin getting vaccinated soon after flu vaccine becomes available, if possible by October, to ensure that as many people as possible are protected before flu season begins. However, as long as flu viruses are circulating in the community, it’s not too late to get vaccinated.

In addition to getting a seasonal flu vaccine if you have not already gotten vaccinated, you can take everyday preventive actions like staying away from sick people and washing your hands to reduce the spread of germs. If you are sick with flu, stay home from work or school to prevent spreading flu to others.

What should I do if I get sick with the flu?

Antiviral drugs are prescription drugs that can be used to treat flu illness. People at high risk of serious flu complications (such as children younger than 2 years, adults 65 and older, pregnant women, and people with certain medical conditions) and people who are very sick with flu (such as those hospitalized because of flu) should get antiviral drugs. Some other people can be treated with antivirals at their health care professional’s discretion. Treating high risk people or people who are very sick with flu with antiviral drugs is very important. Studies show that prompt treatment with antiviral drugs can prevent serious flu complications. Prompt treatment can mean the difference between having a milder illness versus very serious illness that could result in a hospital stay.

Treatment with antivirals works best when begun within 48 hours of getting sick, but can still be beneficial when given later in the course of illness. Antiviral drugs are effective across all age-and risk groups. Studies show that antiviral drugs are under-prescribed for people who are at high risk of complications who get flu. This season, three FDA-approved influenza antiviral drugs are recommended for use in the United States: oseltamivir, zanamivir and peramivir.

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What should I do to protect my loved ones from flu?

Encourage your loved ones to get vaccinated. Vaccination is especially important for people at high risk for serious flu complications, and their close contacts. Also, if you have a loved one who is at high risk of flu complications and who develops flu symptoms, encourage him or her to get a medical evaluation. He or she might need treatment with influenza antiviral drugs. CDC recommends that people who are at high risk for serious flu complications who get the flu be treated with influenza antiviral drugs as quickly as possible. People who are not at high risk for serious flu complications who get the flu may be treated with influenza antiviral drugs at their doctor’s discretion. Children between 6 months and 8 years of age may need two doses of flu vaccine to be fully protected from flu. The two doses should be given at least 4 weeks apart. Your child’s doctor or other health care professional can tell you whether your child needs two doses. If your child does need two doses of vaccine to be fully protected, it is a good idea to begin the vaccination process sooner rather than later. Visit Children, the Flu, and the Flu Vaccine for more information.

Children younger than 6 months are at higher risk of serious flu complications, but are too young to get a flu vaccine. Because of this, safeguarding them from flu is especially important. If you live with or care for an infant younger than 6 months of age, you should get a flu vaccine to help protect them from flu. See Advice for Caregivers of Young Children for more information.

In addition to getting vaccinated, you and your loved ones can take everyday preventive actions like staying away from sick people and washing your hands to reduce the spread of germs. If you are sick with flu, stay home from work or school to prevent spreading influenza to others.

When should I get vaccinated?

CDC recommends that people get vaccinated against flu soon after vaccine becomes available, if possible by October. CDC continues to recommend influenza vaccination as long as influenza viruses are circulating.

It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against the flu.

Doctors and nurses are encouraged to begin vaccinating their patients soon after vaccine becomes available, preferably by October so as not to miss opportunities to vaccinate. Those children aged 6 months through 8 years who need two doses of vaccine should receive the first dose as soon as possible to allow time to get the second dose before the start of flu season. The two doses should be given at least four weeks apart.

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What kind of vaccines are available in the United States for 2015-2016?

A number of different private sector vaccine manufacturers produce flu vaccine for use in the United States. This season both trivalent (three component) and quadrivalent (four component) influenza vaccines are available. Different routes of administration are available for flu vaccines, including intramuscular, intradermal, jet injector and nasal spray vaccine.

This season:

  • Intramuscular (IM) vaccines will be available in both trivalent and quadrivalent formulations. (High dose vaccines, which are IM vaccines, will all be trivalent this season.)
  • For people who are 18 through 64 years old, a jet injector can be used for delivery of one particular trivalent flu vaccine (AFLURIA® by bioCSL Inc.).
  • Nasal spray vaccines will all be quadrivalent this season.
  • Intradermal vaccine will all be quadrivalent.

See Key Facts About Seasonal Flu Vaccine and How Flu Vaccines Are Made for more information.

How much flu vaccine is available this season?

Flu vaccine is produced by private manufacturers, so supply depends on manufacturers. For this season, manufacturers have projected they will provide between 157 to 168 million doses of injectable influenza vaccine for the U.S. market.

When did flu vaccine become available?

The timing of vaccine availability depends on when production is completed and can vary by season. For the 2015-16 season, manufacturers first began vaccine shipments in July and August 2015.

Where can I get a flu vaccine?

Flu vaccines are offered by many doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even by some schools.

Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or work.

Visit the HealthMap Vaccine Finder to locate where you can get a flu vaccine.

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Are there new recommendations for the 2015-2016 influenza season?

Recommendations on the control and prevention of influenza are published annually, in late summer or early fall. Recommendations for the 2015-2016 season were made available in a Morbidity and Mortality Weekly Report (MMWR). During the 2014-2015 flu season, CDC recommended use of the nasal spray vaccine (LAIV) for healthy* children 2 through 8 years of age, when it was immediately available and if the child had no contraindications or precautions to that vaccine. For more information, see the 2014-2015 MMWR Influenza Vaccine Recommendations. However, on February 26, 2015, the Advisory Committee on Immunization Practices (ACIP) did not renew the preferential recommendation for LAIV for the 2015-2016 season. The ACIP recommendations must be approved by the CDC Director at which point they are published in the MMWR and become CDC policy. More information on this vote is available at the CDC Newsroom.

(*“Healthy” in this instance refers to children 2 years through 8 years old who do not have an underlying medical condition that predisposes them to influenza complications.)

Visit What’s New on this Site to sign up and receive updates from the CDC Influenza site.

What flu viruses does this season’s vaccine protect against?

Flu vaccines are designed to protect against the main flu viruses that research suggests will be the most common during the upcoming season. Three kinds of flu viruses commonly circulate among people today: influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses.

All of the 2015-2016 influenza vaccine is made to protect against the following three viruses:

  • an A/California/7/2009 (H1N1)pdm09-like virus
  • an A/Switzerland/9715293/2013 (H3N2)-like virus
  • a B/Phuket/3073/2013-like virus. (This is a B/Yamagata lineage virus)

Some of the 2015-2016 flu vaccine is quadrivalent vaccine and also protects against an additional B virus (B/Brisbane/60/2008-like virus). This is a B/Victoria lineage virus.

Vaccines that give protection against three viruses are called trivalent vaccines. Vaccines that give protection against four viruses are called quadrivalent vaccines.

More information about influenza vaccines is available at Preventing Seasonal Flu With Vaccination.

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What is flu vaccination using a jet injector?

On August 14, 2014, the U.S. Food and Drug Administration (FDA) approved use of one jet injector device (the PharmaJet Stratis 0.5ml Needle-free Jet Injector) for delivery of one particular flu vaccine (AFLURIA® by bioCSL Inc.) in people 18 through 64 years of age. A jet injector is a medical device used for vaccination that uses a high-pressure, narrow stream of fluid to penetrate the skin instead of a hypodermic needle. For more information, see Flu Vaccination by Jet Injector.

How effective is the flu vaccine?

Influenza vaccine effectiveness (VE) can vary from year to year and among different age and risk groups. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work?

In late February, CDC reported flu vaccine effectiveness of nearly 60% this season. This finding is comparable to past estimates for seasons when most circulating flu viruses have been similar to the seasonal flu vaccine. A press release on this topic is available at http://www.cdc.gov/media/releases/2016/flu-vaccine-60-percent.html.

How long does a flu vaccine protect me from getting the flu?

Multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time. The decline in antibodies is influenced by several factors, including the antigen used in the vaccine, the age of the person being vaccinated, and the person's general health (for example, certain chronic health conditions may have an impact on immunity). When most healthy people with regular immune systems are vaccinated, their bodies produce antibodies and they are protected throughout the flu season, even as antibody levels decline over time. Older people and others with weakened immune systems may not generate the same amount of antibodies after vaccination; further, their antibody levels may drop more quickly when compared to young, healthy people.

For everyone, getting vaccinated each year provides the best protection against influenza throughout flu season. It’s important to get a flu vaccine every season, even if you got vaccinated the season before and the viruses in the vaccine have not changed for the current season.

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Is this season's vaccine a good match for circulating viruses?

The most recent CDC report on what viruses are circulating and how similar they are to the vaccine viruses was published in the Morbidity and Mortality Weekly Report Update: Influenza Activity — United States and Worldwide, October 4, 2015–February 5, 2016. Laboratory data so far show that most circulating flu viruses are still like the viruses recommended for the 2015-2016 influenza vaccines.

What is the vaccine composition for the Southern Hemisphere 2016 vaccine?

On September 24, 2015, WHO announced the recommended vaccine virus composition for the 2016 Southern Hemisphere vaccine.

It was recommended that trivalent vaccines for use in the 2016 Southern hemisphere influenza season contain the following:

  • an A/California/7/2009 (H1N1)pdm09-like virus;
  • an A/Hong Kong/4801/2014 (H3N2)-like virus;
  • a B/Brisbane/60/2008-like virus. (a B/Victoria-lineage virus)

It was recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Phuket/3073/2013-like virus (a B/Yamagata-lineage virus).

There are two differences between what was recommended for the 2016 Southern Hemisphere vaccine and what is included in U.S. vaccines this season.

Since the recommended flu vaccine composition for the Southern Hemisphere changed from what is included in the U.S. flu vaccine, does that mean this season’s vaccine is not well-matched to circulating viruses and won’t work as well?

At the most recent World Health Organization (WHO) Consultation and Information Meeting on the Composition of Influenza Virus Vaccines in September 2015, the recommended influenza vaccine virus composition for the 2016 Southern Hemisphere vaccines was updated from the current 2015-2016 U.S. vaccines composition. These updates were made to provide an incremental improvement in the match between vaccine viruses and circulating viruses. Global laboratory data as of September 21, 2015 continues to indicate that most circulating influenza viruses are still antigenically similar to the reference vaccine viruses used for developing the 2015-2016 U.S. vaccines. (No significant antigenic drift has been reported in currently circulating viruses at this time, as occurred last season.) Thus laboratory data available as of September 21, 2015 suggests that vaccination with Northern Hemisphere influenza vaccine should offer protection against the majority of circulating viruses. It is important to note that laboratory data on antigenic similarity is used to suggest how well the vaccine may work, but vaccine effectiveness studies in humans are needed to determine how well the vaccine is actually protecting against illness. Those studies will take place during the 2015-2016 influenza season. CDC continues to recommend annual influenza vaccination. Additional information describing the WHO Consultation and Information Meeting on the Composition of Influenza Virus Vaccines for the Southern Hemisphere for the 2016 Season can be found at http://www.who.int/influenza/vaccines/virus/en/.

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What is the recommended vaccine composition for the U.S. 2016-2017 influenza vaccines?

On March 4, 2016, the Food and Drug Administration's Vaccines and Related Biologics Advisory Committee (VRBPAC) endorsed the WHO-recommended vaccine viruses for use in all U.S. seasonal flu vaccines for the 2016-2017 flu season. It was recommended that trivalent vaccines for use in the 2016-2017 influenza season (Northern Hemisphere winter) contain the following:

  • an A/California/7/2009 (H1N1)pdm09-like virus;
  • an A/Hong Kong/4801/2014 (H3N2)-like virus;
  • a B/Brisbane/60/2008-like virus (B/Victoria lineage).

It was recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Phuket/3073/2013-like virus (B/Yamagata lineage).

The vaccine viruses recommended for inclusion in the 2016-2017 Northern Hemisphere influenza vaccines are the same vaccine viruses that were chosen for inclusion in 2016 Southern Hemisphere seasonal flu vaccines.

More information is available on the FDA VRBPAC web site and via FDA’s summary minutes [43 KB, 4 pages] from the meeting.

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Can the vaccine provide protection even if the vaccine is not a "good" match?

Yes, antibodies made in response to vaccination with one flu virus can sometimes provide protection against different but related viruses. A less than ideal match may result in reduced vaccine effectiveness against the virus that is different from what is in the vaccine, but it can still provide some protection against influenza illness.

In addition, it's important to remember that the flu vaccine contains three or four flu viruses (depending on the type of vaccine you receive) so that even when there is a less than ideal match or lower effectiveness against one virus, the vaccine may protect against the other viruses.

For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend flu vaccination for everyone 6 months and older. Vaccination is particularly important for people at high risk for serious flu complications, and their close contacts.

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Can I get vaccinated and still get the flu?

Yes. It’s possible to get sick with the flu even if you have been vaccinated (although you won’t know for sure unless you get a flu test). This is possible for the following reasons:

  • You may be exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with flu before the vaccine begins to protect you. (About 2 weeks after vaccination, antibodies that provide protection develop in the body.)
  • You may be exposed to a flu virus that is not included in the seasonal flu vaccine. There are many different flu viruses that circulate every year. The flu vaccine is made to protect against the three or four flu viruses that research suggests will be most common.
  • Unfortunately, some people can become infected with a flu virus the flu vaccine is designed to protect against, despite getting vaccinated. Protection provided by flu vaccination can vary widely, based in part on health and age factors of the person getting vaccinated. In general, the flu vaccine works best among healthy younger adults and older children. Some older people and people with certain chronic illnesses may develop less immunity after vaccination. Flu vaccination is not a perfect tool, but it is the best way to protect against flu infection.

What is CDC doing to monitor vaccine effectiveness for the 2015-2016 season?

CDC collaborates with other partners each season to assess how well the seasonal vaccines are working. During the 2015-2016 season, CDC is planning multiple studies on the effectiveness of both the flu shot and the nasal-spray flu vaccine. These studies measure vaccine effectiveness in preventing laboratory-confirmed influenza among persons 6 months of age and older. CDC's seasonal influenza vaccine effectiveness estimates since 2005 are listed on the CDC website.

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Where can I find information about vaccine supply?

Information about flu vaccine supply is available here: Seasonal Influenza Vaccine & Total Doses Distributed

Is there treatment for the flu?

Yes. If you get sick, there are drugs that can treat flu illness. They are called antiviral drugs and they can make your illness milder and make you feel better faster. They also can prevent serious flu-related complications, like pneumonia. For more information about antiviral drugs, visit Treatment (Antiviral Drugs).

What is antiviral resistance?

Antiviral resistance means that a flu virus has changed in such a way that antiviral drugs are less effective. Samples of flu viruses collected from around the United States and worldwide are studied at CDC to determine if they are becoming resistant to any of the FDA-approved influenza antiviral drugs.

How many antiviral resistant viruses have been detected this season?

As of April 9, 2016, CDC and its partner laboratories have detected 11 influenza A(H1N1)pdm09 viruses (0.7%) in the United States during the 2015-16 flu season that are resistant to the antiviral drugs oseltamivir and peramivir. Oseltamivir resistance and peramivir resistance are rare among influenza A (H1N1)pdm09 viruses. The majority of influenza A (H1N1)pdm09 viruses circulating in the United States remain susceptible to currently recommended neuraminidase inhibitor antiviral medications (oseltamivir, peramivir, and zanamivir).

CDC and its public health partners around the world are committed to informing the public of any significant increases in antiviral resistance among circulating influenza viruses. The latest national statistics on antiviral resistance are available in the weekly FluView report.

What is CDC doing to monitor antiviral resistance in the United States during the 2015-2016 season?

CDC is continuing to collect and monitor flu viruses for changes through an established network of domestic and global surveillance systems. Additionally, CDC is working with the state public health departments and the World Health Organization to collect additional information on antiviral resistance in the United States and worldwide. The information collected assists in making informed recommendations regarding use of antiviral drugs to treat influenza.

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How does CDC monitor flu activity?

The Epidemiology and Prevention Branch in the Influenza Division at CDC collects, compiles and analyzes information on influenza activity year round in the United States and produces FluView, a weekly influenza surveillance report, and FluView Interactive, which allows for more in-depth exploration of influenza surveillance data. The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state, local, and territorial health departments, public health and clinical laboratories, vital statistics offices, healthcare providers, clinics, and emergency departments. Information in five categories is collected from nine different data sources that allow CDC to:

  • Find out when and where influenza activity is occurring
  • Track influenza-related illness
  • Determine what influenza viruses are circulating
  • Detect changes in influenza viruses
  • Measure the impact influenza is having on hospitalizations and deaths in the United States

For more information, visit “Overview of Influenza Surveillance in the United States.”

Is CDC doing anything different in terms of virologic surveillance this season?

Yes. In advance of the 2015-2016 season, CDC and the Association of Public Health Laboratories (APHL) shared revised guidelines with public health laboratories for submitting influenza viruses to CDC for testing. The revised guidelines set the recommended number of flu viruses of each type and subtype to be submitted to CDC by each laboratory, along with when and how those viruses should be submitted. 

The revisions were implemented with the goal of yielding a more balanced and comprehensive picture of antigenic, genetic, and antiviral properties of the main groups of flu viruses circulating in the United States. In past seasons, the viruses that have been submitted to CDC have not been fully representative of the main circulating flu viruses (H1N1, H3N2, and B); specifically, predominantly circulating viruses have often been over-represented among submitted samples. It is important to have equally strong surveillance data for the main groups of circulating flu viruses since this data is needed to inform vaccine virus selection and different viruses can predominate from season to season.

What are the guidelines for states in terms of submitting influenza viruses to CDC?

As in previous seasons, each public health laboratory is asked to immediately submit to CDC the first ten flu viruses the laboratory tests this season. Thereafter, each  public health laboratory is asked to submit to their designated National Influenza Surveillance Reference Center* up to two flu-positive specimens from each of the main groups of circulating flu viruses (H1N1, H3N2, B/Yamagata, and B/Victoria), every two weeks. Together the reference centers test the specimens they receive in each two-week period, and then send a subset on to CDC for further analysis. CDC's goal is to receive from public health laboratories a collection of specimens that are representative of currently circulating seasonal flu viruses, including similar numbers of influenza A(H1N1), influenza A(H3N2), B/Yamagata-lineage, and B/Victoria-lineage viruses. If antigenically drifted viruses are detected and additional samples are needed for CDC to make candidate vaccine viruses, additional requests for viruses might be made to laboratories. CDC monitors the timeliness and completeness of submissions, and assists laboratories with technical issues as needed.

*National Influenza Surveillance Reference Centers include California Department of Health, Viral and Rickettsial Disease Laboratory; New York State Department of Health, Wadsworth Center; and Wisconsin State Laboratory of Hygiene.  

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What changes have been made to Fluview for the 2015-2016 Flu Season?

This season, a number of refinements have been made to FluView. Updates to influenza surveillance reporting for the upcoming 2015-2016 flu season include:

  1. Reports from public health and clinical laboratories will be presented separately in both FluView and FluView Interactive
  2. Influenza B lineage data (B/Yamagata and B/Victoria) from public health laboratories will be presented in both FluView and FluView Interactive
  3. Two graphics illustrating the age distribution of influenza positive specimens reported from public health laboratories will be added and;
  4. Mortality data from the National Center for Health Statistics (NCHS) will be the principal tool to track influenza-associated mortality data in the United States.

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Why are virology lab data from public health and clinical laboratories being presented separately in Fluview?

Beginning with the 2015-16 season, reports from public health laboratories and clinical laboratories are being presented separately in both FluView and FluView Interactive. Both sources of information provide valuable information for monitoring influenza activity (see below). This change in reporting has been made to accommodate different influenza testing practices in public health and clinical laboratories.

Public health laboratories primarily test specimens for surveillance purposes to understand what influenza viruses are circulating throughout their jurisdiction and the population groups being affected. Almost all the public health laboratories are using the CDC real-time RT-PCR assay with a fairly standard testing algorithm, allowing for consistent interpretation of virologic data at the national level. Data presented from public health laboratories will include the weekly total number of specimens tested, the number of positive influenza tests, and the number by influenza virus type, subtype, and influenza B lineage. However, because public health laboratories often receive samples that have already tested positive for influenza at a clinical laboratory, this can result in an upward bias in the percent of specimens that test positive for influenza. Because of this, monitoring the percent of specimens testing positive for influenza in a public health laboratory is less useful, but fortunately, is not necessary when clinical laboratory date is available.

Clinical laboratories primarily test respiratory specimens for diagnostic purposes and data from these laboratories provide useful information on the timing and intensity of influenza activity. Data from clinical laboratories include the weekly total number of specimens tested, the number of positive influenza tests, and the percent positive by influenza type. This data is thought to provide a more accurate representation of the percent of specimens testing positive for influenza at any one time in the community.

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Why does Fluview use two different sources of pneumonia and influenza morality surveillance data for assessment of flu associated mortality?

In the past, mortality surveillance was only collected from the 122 Cities Mortality Reporting System (CMRS) and reported by the date the death certificate was registered in the vital records office. A newer system electronically records all U.S. deaths by actual date of death. Beginning with the 2015-2016 season, mortality data from this newer system utilized by the National Center for Health Statistics (NCHS) will be the principal component of the U.S. mortality surveillance system and should provide rapid assessment of flu-associated mortality. Mortality data from the 122 Cities Mortality Surveillance System will continue to be reported in FluView this season before fully transitioning to the electronic mortality surveillance system used by the National Center for Health Statistics (NCHS).

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What are the advantages of using NCHS mortality surveillance data for P&I mortality surveillance?

Recent NCHS efforts to improve timeliness of jurisdiction reporting and modernize national vital statistics infrastructure have created a system capable of supporting near real-time surveillance. Capitalizing on these new capabilities, NCHS and CDC’s Influenza Division have partnered to use NCHS mortality surveillance data for P&I mortality surveillance. Advantages of using the NCHS mortality data include:

  • NCHS data is presented by date of death while 122 CMRS is by date the death certificate was registered. The length of time from when a death occurs and when the death is registered in the vital statistics office can vary considerably. When deaths are presented by date of occurrence, rather than date the death certificate was filed, it provides a more accurate picture of the timing of P&I on overall mortality.
  • On average, the NCHS mortality system will report out almost twice the number of total deaths in a given week compared to the 122 CMRS. And over time, data from NCHS will include 100% of all deaths that occurred in the United States.

Users will be able to download weekly NCHS mortality data by region and/or state on CDC’s website at National Center for Health Statistics Mortality Surveillance Data.

Users of the data should not expect the NCHS mortality surveillance data and the 122 Cities Mortality Reporting System to produce the same percentages. The percent P&I deaths from each system should be compared to the corresponding system specific baselines and thresholds.

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How does CDC track flu deaths?

Unlike flu deaths in children, flu deaths in adults are not nationally reportable, and therefore, CDC cannot say how many adults die from flu each year. However, CDC has two flu surveillance systems that are used to monitor relative levels of flu-associated deaths. One is the “122 Cities Mortality Reporting System” and the other is mortality data collected by the National Center for Health Statistics. Both of these systems track the proportion of death certificates processed that list pneumonia or influenza (P&I) as the underlying or contributing cause of death of the total deaths reported. These systems provide an overall indication of whether flu-associated deaths are elevated, but do not provide an exact number of how many people died from flu. For more information, see Overview of Influenza Surveillance in the United States, “Mortality Surveillance.”

CDC also uses modeling studies to estimate numbers of flu-related deaths, but these studies apply only to past seasons and are not done each year. For more information, see Estimating Seasonal Influenza-Associated Deaths in the United States: CDC Study Confirms Variability of Flu.

Why is it difficult to know how many people die from flu?

There are several factors that make it difficult to determine accurate numbers of deaths caused by flu regardless of reporting. Some of the challenges in counting influenza-associated deaths include the following: the sheer volume of deaths to be counted; not everyone that dies with an influenza-like illness is tested for influenza; and influenza-associated deaths are often a result of complications secondary to underlying medical problems, and this may be difficult to sort out. For more information, see Estimating Seasonal Influenza-Associated Deaths in the United States: CDC Study Confirms Variability of Flu.

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How do I know if I have seasonal influenza or MERS (Middle Eastern Respiratory Syndrome)?

Seasonal influenza and MERS can cause similar respiratory symptoms. However, of these viruses, your symptoms are most likely caused by seasonal influenza. In the United States, fall and winter is the time for flu. While the exact timing and duration of flu seasons vary, flu outbreaks often begin in October and can last as late as May. Most of the time flu activity peaks between December and February. Information about current levels of flu activity is available in CDC’s weekly FluView report.

MERS is not common in the United States. However, in 2014, two people who recently traveled from Saudi Arabia to the United States had MERS. All MERS cases have been linked to countries in or near the Arabian Peninsula.

It is not possible to determine whether a patient has seasonal influenza, or MERS, or an illness due to another pathogen based on symptoms alone. However, there are tests to detect seasonal influenza and MERS. Your doctor will determine if you should be tested for any of these illnesses based on your symptoms, clinical presentation and recent travel history. (For information regarding the signs and symptoms of MERS, and whether you may need to be tested, please review the MERS case definitions.)

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