Questions and Answers

Question & Answer

Q:What is an influenza pandemic?

A:

An influenza pandemic is a global outbreak of a new influenza A virus that is very different from current and recently circulating human seasonal influenza A viruses. Pandemics happen when new (novel) influenza A viruses emerge which are able to infect people easily and spread from person to person in an efficient and sustained way. Because the virus is new to humans, very few people will have natural immunity against the pandemic virus and a vaccine might not be widely available. The new virus can make a lot of people sick. The severity of illness will depend on the characteristics of the virus, whether or not people have immunity to that virus, and whether or not people have certain underlying medical conditions. Influenza pandemics are uncommon; only three influenza pandemics occurred during the 20th century.

Question & Answer

Q:What happens when a pandemic influenza virus emerges?

A:

When a pandemic influenza virus emerges, the virus can spread quickly because most people will not be immune and a vaccine might not be widely available to offer immediate protection. During the 2009 H1N1 pandemic, for example, a new H1N1 virus was first identified in April 2009. By June 2009, that novel H1N1 virus had spread worldwide and the World Health Organization had declared a pandemic. Initial spread of a pandemic influenza virus may occur in multiple disease “waves” that are separated by several months. Schools, childcare centers, workplaces, and other places for mass gatherings may experience more absenteeism. As a pandemic influenza virus spreads, large numbers of people may need medical care worldwide.. Public health and health care systems can become overloaded, with high rates of hospitalizations and deaths. Other critical infrastructure, such as law enforcement, emergency medical services, and transportation industry may also be affected. Later, the pandemic virus continues to circulate as a seasonal influenza A virus. Further changes to the virus may happen subsequently through a process called “antigenic drift.” Antigenic drift refers to small changes in the genes of influenza viruses that happen continually over time as the virus replicates.

Question & Answer

Q:Are there novel flu A viruses that are of extra concern in terms of their pandemic threat?

A:

Any novel influenza A virus, such as those of avian or swine origin, has the potential to cause an influenza pandemic. Some novel flu A viruses are believed to pose a greater pandemic threat and are more concerning to public health officials than others because they have already infected and caused disease in people. Some novel influenza A viruses that have infected people have caused serious illness and death and also have been able to spread in a limited manner from person to person. Spread has not been efficient or sustained in an ongoing way, but these novel influenza A viruses are of extra concern because they already have shown the potential to infect humans and they have caused serious illness and death. Examples of novel influenza A viruses of extra concern because of their potential to cause a severe pandemic include avian influenza A (H5N1) and avian influenza A (H7N9) viruses. These two different avian influenza A viruses have caused sporadic human infections, some limited human-to-human spread and have resulted in critical illness and death in people.

Influenza viruses that normally circulate in pigs also have infected people, including influenza A (H1N1v), (H1N2v) and (H3N2v). When swine viruses are found in people, they are called “variant” viruses; the “v” after the virus name indicates a variant virus. Limited, unsustained spread from person to person also has been detected with these viruses, but in general, these variant viruses have been associated with less severe illness and fewer deaths. In general, human infections with H5N1, H7N9, H1N1v, H1N2v and H3N2v viruses have occurred rarely, but if these viruses were to change in such a way that they were able to infect humans easily and spread from person to person in a sustained manner, a flu pandemic could result.

Question & Answer

Q:Are there vaccines to protect against pandemic flu?

A:

Vaccines to protect against specific influenza viruses have to be made. The federal government has created a stockpile of some vaccines against novel influenza A viruses that could be used in the event of a pandemic, including vaccines against certain avian H5N1 influenza viruses. In this way, if a similar H5N1 virus were to begin a pandemic, some vaccine would already be available.

The Department of Health and Human Services (HHS) is the lead agency for public health preparedness and medical response to an influenza pandemic. Within HHS, the Biomedical Advanced Research and Development Authority (BARDA) Influenza Division is charged with the advanced development and procurement of medical and non-pharmaceutical countermeasures for pandemic influenza preparedness and response.

Question & Answer

Q:How are novel flu A viruses evaluated for their pandemic capacity?

A:

CDC and external influenza experts have developed an Influenza Risk Assessment Tool (IRAT) that assesses the potential pandemic risk posed by specific novel influenza A viruses. Assessment criteria include “properties of the virus,” “attributes of the population,” and “ecology and epidemiology of the virus.”

Question & Answer

Q:How do influenza A viruses change to cause a pandemic?

A:

Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: the hemagglutinin (H) and the neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes (H1 through H18 and N1 through N11). Theoretically, any combination of the 18 hemagglutinins and 11 neuraminidase proteins are possible, but not all have been found in animals and even fewer have been found to infect humans.

While influenza viruses can change in two different ways, one of which is called “antigenic shift” and can result in the emergence of a pandemic influenza virus. Antigenic shift represents an abrupt, major change in an influenza A virus that is different from circulating seasonal influenza A viruses and infects humans. This can result from direct infection of humans with an influenza A virus of animal origin, such as a virus circulating among birds or pigs. Antigenic shift also can happen when an influenza A virus circulating among animals exchanges genetic information with other influenza A viruses in a process called genetic reassortment, and the resultant new virus is able to infect people. For example, exchange of genes between a human influenza A virus and an influenza A virus of animal origin can create a new influenza A virus with a hemagglutinin protein or both a hemagglutinin protein and a neuraminidase protein from an animal influenza A virus. If this new virus causes illness in infected people and can spread easily from person to person, an influenza pandemic can occur.

Question & Answer

Q:How long would it take to develop a new pandemic vaccine?

A:

If a new pandemic influenza virus (not included in the pre-pandemic vaccine stockpile) were to emerge, a vaccine would have to be developed against that virus. First a candidate vaccine virus would need to be made for vaccine production, which takes about two months. Then, using current technology, vaccine production can take about 6 months even after a candidate pandemic influenza vaccine virus has been made. Because of this timeline, early supplies of vaccine might not be enough to meet demand especially if most people may need two doses of vaccine for protective immunity.

Question & Answer

Q:How many doses of pandemic vaccine would each person need?

A:

People with no immunity against a new influenza virus may need two doses to be fully protected against that virus. The first dose primes the immune system and the second dose creates the protective response.

Question & Answer

Q:What treatments are available for pandemic flu?

A:

The same antiviral drugs that are used to treat seasonal influenza viruses may be useful for treating pandemic influenza depending upon whether the pandemic influenza virus is susceptible or resistant to available antiviral drugs. Antiviral drugs are prescription medicines (pills, liquid or an inhaled powder) that fight against the influenza viruses that infect your respiratory tract. Antiviral drugs are not sold over-the-counter and are different from prescription antibiotics that treat bacterial infections. You can only get antivirals if you have a prescription from your doctor or health care provider.

Question & Answer

Q:Where do pandemic influenza viruses come from?

A:

Different animals—including birds and pigs—are hosts to influenza A viruses that do not normally infect people. Influenza A viruses are constantly changing, making it possible on very rare occasions for non-human influenza viruses to change in such a way that they can infect people easily and spread efficiently from person to person.

Question & Answer

Q:Will seasonal flu vaccines protect against pandemic flu?

A:

It is unlikely that seasonal flu vaccines would protect against a pandemic influenza virus. Seasonal flu vaccines that are used annually protect against currently circulating human influenza A and B viruses. They are not designed to protect against new influenza A viruses. A pandemic influenza virus would be very different from circulating seasonal influenza A viruses and thus seasonal vaccines would not be expected to offer protection.