H3N2v and You
H3N2v is a non-human influenza virus that normally circulates in pigs and that has infected humans. Viruses that normally circulate in pigs are “swine influenza viruses.” When these viruses infect humans, they are termed “variant” viruses.
In 2011, a specific H3N2 virus was detected with genes from avian, swine and human viruses and the 2009 H1N1 pandemic virus M gene. The virus was circulating in pigs in 2010 and was first detected in people in 2011. The acquisition of the 2009 M gene may make this virus infect humans more easily than is typical for other swine influenza viruses. There were 12 human infections in the United States with this virus, termed H3N2v, in 2011; most were associated with exposure to pigs. In 2012, 309 cases of H3N2v infection across 12 states were detected. In 2013, 19 cases of H3N2v infection in five states were detected.
See Case Count: Detected U.S. Human Infections with H3N2v by State since August 2011 for information about H3N2v cases, hospitalizations and deaths that have been reported to CDC.
Influenza viruses can spread from pigs to people and from people to pigs. Spread from infected pigs to humans is thought to happen in the same way that seasonal influenza viruses spread between people; mainly through infected droplets created when an infected pig coughs or sneezes. If these droplets land in your nose or mouth, or you inhale them, you can be infected. There also is some evidence that you might get infected by touching something that has virus on it and then touching your own mouth or nose. A third possible way to get infected is to inhale particles containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common.
Symptoms of H3N2v infection are similar to those of seasonal flu viruses and can include fever and respiratory symptoms, such as cough and runny nose, and possibly other symptoms, such as body aches, nausea, vomiting, or diarrhea.
CDC is concerned about H3N2v for a few reasons.
First, infections with influenza viruses (including variant viruses like H3N2v) can sometimes cause severe disease, even in healthy people. This can include complications (like pneumonia), which can require hospitalization, and sometimes result in death.
Second, this virus seems to spread more easily to humans from pigs than other swine influenza viruses.
Third, influenza viruses are always changing. It’s possible the H3N2v virus could change and begin spreading easily from person to person.
Fourth, studies conducted by CDC and others have indicated that children younger than about 10 years old have little to no immunity against H3N2v virus. Adults seem to have more immunity, perhaps because they might have been previously exposed to similar viruses in their lifetimes.
Currently, the severity of human illness associated with H3N2v resembles that of seasonal flu.
Keep in mind that even seasonal influenza can be a serious disease. Sometimes seasonal influenza can lead to complications (like pneumonia). It also can lead to hospitalization and even death.
Early steps to make a vaccine against H3N2v have been taken, but no decision to mass produce such a vaccine has been made.Top of Page
Seasonal flu vaccine will not protect against H3N2v. Seasonal flu vaccines protect against seasonal influenza viruses. CDC recommends that everyone 6 months and older get a seasonal flu vaccine each year.
Yes. The same influenza antiviral drugs used to treat seasonal flu can treat H3N2v in children and adults. The currently recommended drugs – oseltamivir and zanamivir – are available by prescription from your doctor.
Early treatment works better and may be especially important for people with a high risk condition.
If you are prescribed antiviral drugs by your doctor, you should finish all of the medication, according to your doctor’s instructions.
People who are at high risk of developing complications if they get seasonal flu include the following: children younger than 5 years, people 65 years and older, pregnant women, and people with certain long-term health conditions (like asthma, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions).
A full list of people at high risk of flu related complications is available at People at High Risk of Developing Flu-Related Complications. These same groups of people are thought to be at high risk of developing serious complications from H3N2v infection.
CDC has issued guidance for people attending fairs where swine might be present this fair season, including additional precautions for people who are at high risk for serious flu complications.Top of Page
No. Influenza viruses have not been shown to be transmissible to people through eating pork (pig meat).
The H3N2v virus was found in U.S. pigs in 2010 and in people in 2011.
In 2011, 12 U.S. residents were found to be infected with H3N2v. In 2012, 309 cases of H3N2v were reported in the United States. In 2013, H3N2v cases were first detected in June.
See Influenza A (H3N2) Variant Virus Outbreaks for the latest information regarding the number of cases, hospitalizations and deaths reported to CDC.
Most H3N2v infections have occurred in children with exposure to swine; many have occurred at agricultural fairs.Top of Page
CDC continues to communicate regularly with states, and states have continued with surveillance and laboratory activities to detect human cases of H3N2v.
CDC also continues to monitor the situation closely. In particular, CDC’s Influenza Division examines the genes of many of the H3N2v viruses that are shipped by state public health laboratories to CDC to ensure that the virus is not changing in key ways. To date, no significant changes in the H3N2v virus have been detected.
See Take Action to Prevent the Spread of Flu Between People and Pigs at Fairs for a list of steps you can take to protect yourself against H3N2v.
In particular, if you are at high risk of serious flu complications, avoid pigs and swine barns at the fair this year.
Should I avoid agricultural fairs where swine are present?
It’s not necessary to avoid agricultural fairs where swine are present. However, you should take steps to protect yourself against H3N2v if you do attend agricultural fairs, particularly where swine are present.
If you are at high risk of serious flu complications, avoid pigs and swine barns at the fair this year.Top of Page
People with health or age factors that put them at high risk for serious flu complications should avoid pigs and swine barns.
As always, take time to get a seasonal influenza vaccine as soon as flu vaccine becomes available in your community, to protect yourself from the seasonal influenza viruses that are most likely to circulate this season.
No, you cannot always tell if a pig has a flu virus just by looking at the pig. Some pigs infected with influenza may have no symptoms at all. See Key Facts About Swine Influenza (Swine Flu) in Pigs for a list of signs of flu in pigs.
No, H3N2v is different. H3N2v is a variant virus that is spreading in pigs and has infected some humans.Top of Page