A number of human infections with a variant influenza A H3N2 virus (“H3N2v”) have been detected in the United States since August 2011 (see Case Count: Detected U.S. Human Infections with H3N2v by State since August 2011). These are viruses that do not usually infect people but that occur in pigs and that are very different from human seasonal H3N2 viruses.
Most of the infections with H3N2v have occurred after contact with pigs. Influenza viruses are thought to spread from infected pigs to humans in the same way that seasonal influenza viruses spread between people. Mainly, the spread of influenza happens when droplets infected with influenza – spread through the air after an infected pig coughs or sneezes – land in your nose or mouth, or when the droplets are inhaled. There is also 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 way to possibly get infected is to inhale particles containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common. In some cases, the H3N2v virus seems to have spread from person-to-person. So far spread has not continued beyond one or two people. The symptoms and severity of H3N2v illness have been similar to seasonal flu.
The H3N2v virus is related to human flu viruses from the 1990s, so adults should have some immunity against these viruses, but young children probably do not. Early steps to make a vaccine against H3N2v have been taken. Seasonal vaccine is not designed to protect against H3N2v. For more information, please visit Information on H3N2 Variant Influenza A Viruses.
The risk of infection and spread of influenza viruses between people, including H3N2v, can be reduced by taking a combination of actions. CDC recommends you:
- Take everyday preventive actions, including:
- Try to avoid close contact with sick people.
- Cover your nose and mouth with a tissue when you cough or sneeze. (Throw the tissue in the trash after you use it.)
- Wash your hands often with soap and water, especially after you cough or sneeze. If soap and water are not available, an alcohol-based hand rub may be used.
- Avoid touching your eyes, nose or mouth. Germs spread that way.
- If you are sick, stay home from work or school until your illness is over.
Take Action to Prevent the Spread of Flu Viruses Between People and Pigs
These actions can reduce the risk of influenza viruses spreading from pigs to people.
- Don’t take food or drink into pig areas; don’t eat, drink or put anything in your mouth in pig areas.
- Don’t take toys, pacifiers, cups, baby bottles, strollers, or similar items into pig areas.
- Wash your hands often with soap and running water before and after exposure to pigs. If soap and water are not available, use an alcohol-based hand rub.
- Avoid close contact with pigs that look or act ill.
- Take protective measures if you must come in contact with pigs that are known or suspected to be sick. This includes minimizing contact with pigs and wearing personal protective equipment like protective clothing, gloves and masks that cover your mouth and nose when contact is required.
- To further reduce the risk of infection, minimize contact with pigs in the pig barn and arenas.
- Watch your pig (if you have one) for signs of illness and call a veterinarian if you suspect it might be sick.
- Avoid contact with pigs if you have flu-like symptoms. Wait 7 days after your illness started or until you have been without fever for 24 hours without the use of fever-reducing medications, whichever is longer. If you must have contact with pigs while you are sick, take the protective actions listed above.
Note that certain people are at higher risk for serious flu complications if they get infected with influenza viruses, including H3N2v. This includes children younger than 5 years, people 65 years and older, pregnant women, and people with certain long-term health conditions (like asthma and other lung disease, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions). CDC has issued guidance for “high risk” people attending fairs where swine might be present. Those people should avoid pigs and swine barns at fairs.
Additional information and materials, including educational posters that can be displayed around animal exhibits, also are available at the following web page NASPHV: Zoonotic Influenza.
Swine influenza has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs. For more information about the proper handling and preparation of pork, visit the USDA website fact sheet Fresh Pork from Farm to Table.
At this time, CDC recommends the following:
- If you go to a doctor for flu symptoms (see below) following direct or close contact with swine, tell your doctor about this exposure.
- If you have flu symptoms, follow CDC’s regular recommendations for seeking treatment for influenza.
- If you have symptoms of flu and are very sick or worried about your illness contact your health care provider.
- Certain people are at greater risk of serious flu-related complications (including young children, elderly persons, pregnant women and people with certain long-term medical conditions) and this is true both for seasonal flu and novel flu virus infections. (A full list of people at higher risk of flu related complications is available at People at High Risk of Developing Flu-Related Complications.)
- If these people develop ILI, it’s best for them to contact their doctor as soon as possible. (The majority of recent H3N2v cases have been in children.)
- Your doctor may prescribe antiviral drugs that can treat the flu, including H3N2v. These drugs work better for treatment the sooner they are started. If you are prescribed antiviral drugs by your doctor, you should finish all of the medication, according to your doctor’s instructions.
- Also, whenever you have flu symptoms and are seeing a health care provider, always remember to tell them if you have asthma, diabetes, heart disease, neurological and neurodevelopmental conditions, are pregnant, or are older than 65 or younger than 5 years. These conditions and age factors put you at high risk of serious complications if you have the flu.
- Flu signs and symptoms usually include fever and respiratory symptoms, such as cough and runny nose, and possibly other symptoms, such as body aches, nausea, vomiting, or diarrhea.
- Health care providers will determine whether influenza testing and possible treatment are needed.
- There are influenza antiviral drugs that can be used to treat infection with H3N2v viruses as well as seasonal influenza viruses. More information about influenza antiviral drugs is available at Treatment (Antiviral Drugs).
Information and materials, including educational posters[389 KB, 1 page] that can be displayed around animal exhibits, are available in Compendium of Measures to Prevent Disease Associated with Animals in Public Settings, 2013.
Dr. Lyn Finelli discusses CDC’s recommendations for reducing the risk of infection with H3N2v flu viruses for fairgoers and swine exhibitors.