The H1N1 swine flu virus appeared in the U.S. in April 2009 and never went away. After sweeping the globe, U.S. H1N1 swine flu cases surged as schools opened in the fall. What is H1N1 swine flu? What can we do about it? WebMD answers your questions.
- What is swine flu?
- What are swine flu symptoms?
- Who is at highest risk of H1N1 swine flu?
- Help! I've been exposed to swine flu. What should I do?
- If I think I have swine flu, what should I do?
- How does swine flu spread?
- How is swine flu treated?
- Is there a vaccine against the new swine flu virus?
- I had a flu vaccine this season. Am I protected against swine flu?
- How can I prevent swine flu infection?
- Should I wear a face mask or respirator?
- How long does the flu virus survive on surfaces?
- Can I still eat pork?
- What else should I be doing during the swine flu pandemic?
- How severe is swine flu?
- Have there been previous swine flu outbreaks?
- I was vaccinated against the 1976 swine flu virus. Am I still protected?
- How many people have swine flu?
- How serious is the public health threat of a swine flu epidemic?
What is swine flu?
Swine flu, also known as 2009 H1N1 type A influenza, is a human disease. People get the disease from other people, not from pigs.
The disease originally was nicknamed swine flu because the virus that causes the disease originally jumped to humans from the live pigs in which it evolved. The virus is a "reassortant" -- a mix of genes from swine, bird, and human flu viruses. Scientists are still arguing about what the virus should be called, but most people know it as the H1N1 swine flu virus.
The swine flu viruses that usually spread among pigs aren't the same as human flu viruses. Swine flu doesn't often infect people, and the rare human cases that have occurred in the past have mainly affected people who had direct contact with pigs. But the current "swine flu" outbreak is different. It's caused by a new swine flu virus that has changed in ways that allow it to spread from person to person -- among people who haven't had any contact with pigs.
That makes it a human flu virus. To distinguish it from flu viruses that infect mainly pigs and from the seasonal influenza A H1N1 viruses that have been in circulation for many years, the CDC calls the virus "2009 H1N1 virus." Other names include "novel H1N1" or nH1N1, "quadruple assortant H1N1," and "2009 pandemic H1N1."
Many people have at least partial immunity to seasonal H1N1 viruses because they've been infected with or vaccinated against this flu bug. These viruses "drift" genetically, which is why the flu vaccine has to be tweaked from time to time.
But the H1N1 swine flu is not the usual "drift variant" of H1N1. It came to humans from a different line of evolution. That means most people have no natural immunity to H1N1 swine flu. The normal seasonal flu shot does not protect against this new virus.
Some people who may have had seasonal H1N1 flu before 1957 might have a little bit of protective immunity against the new virus. That's because seasonal H1N1 flu strains that circulated before 1957 (and which were replaced by the 1957 pandemic flu bug) were genetically closer to the 2009 H1N1 swine flu. This protection is not complete. While relatively few elderly people have had H1N1 swine flu, many of those who did get the disease became severely ill.
What are swine flu symptoms?
Symptoms of H1N1 swine flu are like regular flu symptoms and include fever, cough, sore throat, runny nose, body aches, headache, chills, and fatigue. Many people with swine flu have had diarrhea and vomiting. But these symptoms can also be caused by many other conditions. That means that you and your doctor can't know, just based on your symptoms, if you've got swine flu. Health care professionals may offer a rapid flu test, although a negative result doesn't mean you don't have the flu. The accuracy of the test depends on the quality of the manufacturer’s test, the sample collection method, and how much virus a person is shedding at the time of testing.
Like seasonal flu, pandemic swine flu can cause neurologic symptoms in children. These events are rare, but, as cases associated with seasonal flu have shown, they can be very severe and often fatal. Symptoms include seizures or changes in mental status (confusion or sudden cognitive or behavioral changes). It's not clear why these symptoms occur, although they may be caused by Reye's syndrome. Reye's syndrome usually occurs in children with a viral illness who have taken aspirin -- something that should always be avoided.
Only lab tests can definitively show whether you've got swine flu. State health departments can do these tests. During the peak of the pandemic, these tests were reserved for patients with severe flu symptoms.
Who is at highest risk from H1N1 swine flu?
Most U.S. cases of H1N1 swine flu have been in children and young adults. It's not clear whether this will change as the 2009 H1N1 pandemic wanes and the virus becomes a seasonal flu bug.
But certain groups are at particularly high risk of severe disease or bad outcomes if they get the flu:
- Pregnant women are six times more likely to have severe flu disease than women who are not pregnant.
- Young children, especially those under 2 years of age
- People with asthma.
- People with COPD or other chronic lung conditions
- People with cardiovascular conditions (except high blood pressure)
- People with liver problems
- People with kidney problems
- People with blood disorders, including sickle cell disease
- People with neurologic disorders
- People with neuromuscular disorders
- People with metabolic disorders, including diabetes
- People with immune suppression, including HIV infection and medications that suppress the immune system, such as cancer chemotherapy or anti-rejection drugs for transplants
- Residents of a nursing home or other chronic-care facility
- Elderly people are at high risk of severe flu disease -- if they get it. Relatively few swine flu cases have been seen in people over age 65.
People in these groups should seek medical care as soon as they get flu symptoms.
A striking number of adults who developed severe swine flu complications have been morbidly obese. While the vast majority of extremely obese people suffer respiratory problems and/or diabetes, which make flu worse, obesity itself is now considered a risk for serious 2009 H1N1 flu.
Help! I've been exposed to H1N1 swine flu. What should I do?
If you come into close contact with a person who has the flu -- especially if that person did not cover a cough or sneeze when you were within 6 feet -- you've been exposed. Exposure does not guarantee infection or illness, so there's still a good chance you won't get the flu.
What you should do next depends on your risk for getting severe disease and on the risk of severe disease in others with whom you cannot avoid contact.
If you have any of the conditions that put you at increased risk of severe H1N1 swine flu -- pregnancy, asthma, lung disease, diabetes, heart disease, neurologic disease, immune suppression, or other chronic conditions -- it may be riskier for you to get the flu than for other people. That also goes for children under age 2 years, young people under age 19 taking daily aspirin therapy, and people over age 65. And if you are a caretaker for an infant under age 6 months, that child is at risk of severe disease if they catches the flu from you.
The CDC advises against the use of the anti-flu drugs Tamiflu and Relenza to keep exposed people from getting the flu. That's because most of the few cases of drug-resistant H1N1 swine flu have popped up in people taking Tamiflu to prevent flu.
Instead, the CDC advises at-risk individuals to call their health care providers if they are exposed to flu. The provider may choose to write a prescription for Tamiflu or Relenza, to be filled only if flu symptoms appear. Or the provider may ask the patient to call again at the first sign of flu, at which time a prescription will be written.
Don't wait for a rapid flu test. The tests often give negative results even in people who really have H1N1 swine flu. If you've got flu symptoms and you're at risk of severe disease, start taking flu drugs right away. The drugs work best when taken within 48 hours of the first symptom, although even when taken much later they can prevent severe illness.
What if you aren't at risk and don't have to care for an infant?
In that case, the CDC's basic advice is for you to stock up on chicken soup, line up some tender loving care, and plan to stay home if you get sick. The vast majority of otherwise healthy people who get H1N1 swine flu pull through just fine, after a few miserable days of flu symptoms.
BUT: The flu is a tricky disease. If you do get the flu and develop any of the warning signs of severe disease -- especially trouble breathing, or getting worse after feeling better -- call your doctor right away. It's especially important to watch younger children for signs of severe disease, such as irritability, refusal to eat, trouble waking, bluish or grayish skin color, or a fever that goes down and then shoots back up.
If I think I have swine flu, what should I do? When should I see my doctor?
If you have flu symptoms, stay home, and when you cough or sneeze, cover your mouth and nose with a tissue. Afterward, throw the tissue in the trash and wash your hands. That will help prevent your flu from spreading. If you can do it comfortably, wear a surgical mask if you must be around others.
If you have only mild flu symptoms, you do not need medical attention unless your illness gets worse. But if you are in one of the groups at high risk of severe disease, contact your doctor at the first sign of flu-like illness. In such cases, the CDC recommends that people call or email their doctor before rushing to an emergency room.
But heed these signs of a medical emergency:
Children should be given urgent medical attention if they:
- Have fast breathing or trouble breathing
- Have bluish or gray skin color
- Are not drinking enough fluid
- Are not waking up or not interacting
- Have severe or persistent vomiting
- Are so irritable that the child does not want to be held
- Have flu-like symptoms that improve but then return with fever and a worse cough
- Have fever with a rash
- Have a fever and then have a seizure or sudden mental or behavioral change.
Adults should seek urgent medical attention if they have:
- Difficulty breathing or shortness of breath
- Pain or pressure in the chest or abdomen
- Sudden dizziness
- Severe or persistent vomiting
- Flu-like symptoms that improve, but then come back with worsening fever or cough
Keep in mind that your doctor will not be able to determine whether you have H1N1 swine flu, but they may take a sample from you and send it to a state health department lab for testing to see if it's swine flu. If your doctor suspects swine flu, they would be able to write you a prescription for Tamiflu or Relenza.
These antiviral medications aren't a question of life or death for the vast majority of people. Most U.S. swine flu patients have made a full recovery without antiviral drugs.
How does swine flu spread? Is it airborne?
The new H1N1 swine flu virus apparently spreads just like regular flu. You could pick up germs directly from airborne droplets from the cough or sneeze of an infected person. You could also pick up the virus by touching an object contaminated by the cough or touch of an infected person and then touching your eyes, mouth, or nose. That's why you should make washing your hands a habit, even when you're not ill. Infected people can start spreading flu germs up to a day before symptoms start, and for up to seven days after getting sick, according to the CDC.
The H1N1 swine flu virus, like the seasonal flu virus, can become airborne if you cough or sneeze without covering your nose and mouth, sending germs into the air. Ferret studies suggest that swine flu spreads less easily by small, airborne droplets than does seasonal flu. But it does spread by this route, and it may begin to spread even more readily as the new virus fully adapts to humans.
The H1N1 swine flu virus is a human virus spread by people and not by pigs. The only way to get the new swine flu is from another person.
How is swine flu treated?
PandemicH1N1 swine flu virus is sensitive to the antiviral drugs Tamiflu and Relenza. These antiviral drugs are most effective when taken within 48 hours of the start of flu symptoms. It's resistant to older flu drugs.
A third antiviral drug, peramivir, can be used only in hospitalized patients with severe flu. Peramivir is an intravenous drug approved for use under the FDA's Emergency Use Authorization.
Not everyone needs treatment with these anti-flu drugs. Most people who come down with H1N1 swine flu recover fully -- without antiviral treatment.
But the CDC strongly recommends antiviral treatment for people at risk of severe flu complications who come down with flu-like symptoms. Since it's very important to start these drugs soon after symptoms appear, doctors should offer treatment to at-risk patients if they suspect they have the flu. Doctors should not rely on rapid flu tests (they are too unreliable for definitive diagnosis) or wait for results of lab-based tests (because they take too long).
Early treatment is so important that the CDC suggests doctors offer a Tamiflu or Relenza prescription to at-risk patients. If these patients develop flu-like symptoms, they would call their doctor, and based on the doctor's clinical judgment, the patient could then simply fill the prescription.
Many people who have died of H1N1 swine flu had bacterial co-infections, particularly pneumococcal infections. There's a vaccine against pneumococcal infections. It's routine for children and recommended for adults with underlying health conditions, smokers, or people over age 65. If your flu symptoms get worse after getting better, call your doctor. You may need treatment with antibiotic medications.
Is there enough Tamiflu and Relenza to go around? Federal and state stockpiles are large enough to treat at-risk patients with flu symptoms. But there isn't enough to offer treatment to otherwise healthy people who may have the flu. And health officials have asked people not to hoard Tamiflu or Relenza.
Tamiflu and Relenza can prevent swine flu, but the CDC urges even at-risk people to try to avoid using the drugs in this way. Not only is supply insufficient for preventive use, but preventive use appears to be a major factor in the few cases of drug-resistant H1N1 swine flu that have appeared.
There are situations in which preventive use of Tamiflu or Relenza may be appropriate for an at-risk person who must come into close contact with someone who has the flu. But the CDC suggests that doctors consider a "watchful waiting" approach. In this case, the at-risk person would wait to fill the prescription only if they actually developed flu symptoms.
Is there a vaccine against the new swine flu virus?
Yes. The problem was that the main wave of the pandemic hit the U.S. in September 2009. Vaccine production was delayed by a lower-than-expected yield of vaccine from the chicken eggs in which vaccine virus is grown. It wasn't until the end of January 2010 that every U.S. resident who wanted the vaccine could get it. By then, many people either already had the flu or figured the danger had passed.
By midsummer 2010, there was only a trickle of H1N1 infections, but deaths and hospitalizations continued among at-risk people who had not been vaccinated.
When the vaccine for the 2010-2011 flu season is ready, it will include the 2009 H1N1 vaccine as well as a vaccine against two other seasonal flu bugs.
Clinical tests show the 2009 H1N1 vaccine works remarkably well. People ages 10 and older need only one dose of the vaccine. Protection begins about eight days after vaccination. Kids under age 10 will need two vaccinations, given three weeks apart. The vaccine is highly effective -- and, according to early results from clinical trials, very safe -- in pregnant women.
Extensive safety surveillance, as of June 2010, showed no problems linked to the vaccine. Guillian-Barre syndrome (GBS), a rare neurological syndrome, can be triggered by flu vaccines. The seasonal flu vaccine causes about one extra case of GBS among every million people vaccinated. CDC data suggest that the 2009 H1N1 vaccine increased GBS cases by about the same amount.
Does this mean the swine flu vaccine is 100% safe? No. Rare vaccine reactions do happen, even with the seasonal flu vaccine. But flu experts at the National Institutes of Health, the CDC, and the FDA note that getting the flu is far more risky than getting the vaccine.
Spurred by the safety concerns that sank vaccination efforts during the 1976 swine flu scare (a scare caused by a very different generation of flu vaccine against a very different swine flu virus), federal officials have increased efforts to track the safety of the H1N1 swine flu vaccine. In addition to beefing up the CDC's and FDA's vaccine adverse-event surveillance system, health care organizations, academic medical centers, and the U.S. military will be helping track vaccine safety. An advisory board made up of non-government advisors performs frequent reviews of the safety data.
The vaccine will be available to all U.S. residents. As we're all in this together, nobody will be asked to provide proof of citizenship or legal immigration.
Vaccination is not mandatory for most U.S. residents. Active-duty military and Defense Department personnel are required to get the vaccine. And health-care workers may be required to get the vaccine by their employers or by state regulations.
I had a flu vaccine this season. Am I protected against swine flu?
No. The 2009-2010 seasonal flu vaccine did not protect against the new swine flu virus.
But the 2010-2011 seasonal flu vaccine will protect against the 2009 H1N1 swine flu. Don't wait for this vaccine if you are at high risk of serious flu. The 2009 H1N1 virus is still circulating. While there have been few infections in 2010, hospitalizations and deaths continue.
How can I prevent swine flu infection?
The CDC recommends taking these steps:
- Wash your hands regularly with soap and water, especially after coughing or sneezing. Scrub for at least 20 seconds and rinse thoroughly.
- If soap and water are not available, wash your hands with an alcohol-based hand gel. Rub your hands together until the alcohol dries completely.
- Avoid close contact -- that is, being within 6 feet -- with people who have flu-like symptoms.
- Avoid touching your mouth, nose, or eyes. That's not easy to do, so keep those hands clean.
- If you have flu-like symptoms -- fever plus at least cough or sore throat or other flu symptoms -- stay home for seven days after symptoms begin or until you've been symptom-free for 24 hours -- whichever is longer.
- Wear a face mask (consider using an N95 respirator) if you must come into close contact with a sick person. "Close contact" means within 6 feet. Note: There is no definitive proof that a face mask prevents flu transmission. Do not rely solely on a face mask to prevent infection.
- Wear an N95 respirator if helping a sick person with a nebulizer, inhaler, or other respiratory treatment. Note: There is no definitive proof that a respirator prevents flu transmission. Do not rely solely on a respirator to prevent infection.
- People who have or are suspected of having swine flu should wear a face mask, if available and tolerable, when sharing common spaces with other household members, when outside the home, or when near children or infants.
- Breastfeeding mothers with swine flu symptoms should express their breast milk, and the child should be fed by someone else.
Should I wear a face mask or respirator?
Short answer: Maybe. Face masks and respirators may very well offer extra protection, but should not be your first line of defense against either pandemic or seasonal flu.
Every day, newspapers carry pictures of people wearing face masks to prevent swine flu transmission. But very little is known about whether face masks actually protect against the flu.
There's a difference between a face mask and a respirator. A face mask does not seal tightly to the face. Face masks include masks labeled as surgical, dental, medical procedure, isolation, or laser masks. Respirators are N95- or higher-rated filtering face pieces that fit snugly to the face. Respirators filter out virus particles when correctly adjusted -- which is not as simple as it sounds. But it's hard to breathe through them for extended periods, and they cannot be worn by children or by people with facial hair.
People who have flu-like symptoms should carry disposable tissues to cover their coughs and sneezes. When going out in public, or when sharing common spaces around the home with family members, they should put on a face mask -- if one is available and tolerable.
People not at risk of severe flu illness can best protect themselves from swine flu with frequent hand washing and by staying at least 6 feet away from people with flu symptoms. But if swine flu is circulating in the community, a face mask or respirator may be protective in crowded public places.
People at increased risk of severe flu illness -- pregnant women, for example -- should add a face mask to these tried-and-true precautions when providing assistance to a person with flu-like illness. And anyone else who cannot avoid close contact with someone who has swine flu (if you must hold a sick infant, for example) may try using a face mask or respirator.
How long does the flu virus survive on surfaces?
Flu bugs can survive for hours on surfaces. One study showed that flu viruses can live for up to 48 hours on hard, nonporous surfaces such as stainless steel and for up to 12 hours on cloth and tissues. The virus seems to survive for only minutes on your hands -- but that's plenty of time for you to transfer it to your mouth, nose, or eyes.
Can I still eat pork?
Yes. You can't get swine flu by eating pork, bacon, ham, or other foods that come from pigs. You can only get the 2009 H1N1 swine flu from another person.
What else should I be doing during the swine flu pandemic?
Keep informed of what's going on in your community. Your state and local health departments may have important information if swine flu develops in your area. For instance, parents might want to consider what they would do if their child's school temporarily closed because of flu. Don't panic, but a little planning wouldn't hurt.
Here's the advice from the U.S. government's pandemicflu.gov web site:
To plan for a pandemic:
- Store a two-week supply of water and food. During a pandemic, if you cannot get to a store, or if stores are out of supplies, it will be important for you to have extra supplies on hand. This can be useful in other types of emergencies, such as power outages and disasters.
- Periodically check your regular prescription drugs to ensure a continuous supply in your home.
- Have any nonprescription drugs and other health supplies on hand, including pain relievers, stomach remedies, cough and cold medicines, fluids with electrolytes, and vitamins.
- Talk with family members and loved ones about how they would be cared for if they got sick, or what will be needed to care for them in your home.
- Volunteer with local groups to prepare and assist with emergency response.
- Get involved in your community as it works to prepare for an influenza pandemic.
Items to have on hand for an extended stay at home:
Examples of food and non-perishables
Examples of medical, health, and emergency supplies
• Ready-to-eat canned meats, fish, fruits, vegetables, beans, and soups
• Prescribed medical supplies such as glucose and blood-pressure monitoring equipment
• Protein or fruit bars
• Soap and water, or alcohol-based (60-95%) hand wash
• Dry cereal or granola
• Medicines for fever, such as acetaminophen or ibuprofen
• Peanut butter or nuts
• Dried fruit
• Anti-diarrheal medication
• Canned juices
• Fluids with electrolytes
• Bottled water
• Cleansing agent/soap
• Canned or jarred baby food and formula
• Pet food
• Other non-perishable items
• Portable radio
• Manual can opener
• Garbage bags
• Tissues, toilet paper, disposable diapers
How severe is swine flu?
Theseverity of cases in the current swine flu outbreak has varied widely, from mild cases to fatalities. Most U.S. cases have been mild, but there have been a number of tragic deaths and hundreds of hospitalizations -- mostly in young people aged 5 to 24. Pregnant women have been particularly vulnerable to severe flu and death.
Like seasonal flu, children who get swine flu can have serious neurological complications such as seizures and Reye's syndrome. But as with seasonal flu, these complications fortunately are rare.
Studies of the swine flu virus show that it is more infectious to lung cells than are seasonal flu viruses. But studies also suggest that the swine flu virus is less well adapted to humans and may be harder to inhale deep into the lungs.
Flu viruses change all the time. The way the pandemic swine flu virus evolved suggests that it is particularly liable to swap gene segments with other flu viruses. But so far, the swine flu virus hasn't changed much. That's good news, as the vast majority of swine flu cases have been mild. And it's also good news for the swine flu vaccine, which is based on swine flu strains isolated early in the pandemic.
It's impossible to know whether the virus will become more deadly. Scientists are watching closely to see which way the new swine flu virus is heading -- but health experts warn that flu viruses are notoriously hard to predict.
But there's a lot of planning you can do. CDC officials predict that just about every U.S. community will have H1N1 swine flu cases. It's possible some schools in your community may temporarily close, or even that major gatherings may be canceled. So make contingency plans just in case you are affected. For more information on preparedness planning, see the U.S. government's pandemicflu.gov web site.
Have there been previous swine flu oubtreaks?
Yes, but never before has there been a swine flu pandemic. Pigs can be infected with a wide range of flu viruses. Once in a while, a person in close contact with pigs becomes infected. It's not possible to get swine flu from eating pork.
In 1976, there was an outbreak of swine-origin flu among military recruits in Ft. Dix, N.J. Some of these young men died. Health experts on the lookout for the next flu pandemic thought the infection would spread further and launched a vaccination campaign. As it turned out, the virus never spread and disappeared on its own. Because the vaccine carried a small increased risk of severe neurological problems -- and because there was no benefit in a vaccine for a pandemic that never happened -- the vaccination campaign was stopped.
I was vaccinated against the 1976 swine flu virus. Am I still protected?
Probably not. The new swine flu virus is different from the 1976 virus. And it's not clear whether a vaccine given more than 30 years ago would still be effective.
How many people have swine flu?
That's no longer possible to answer definitively, because so many people have become infected that most nations can no longer test everyone suspected of having H1N1 swine flu. The CDC counts hospitalizations and deaths, but even these figures underestimate the true extent of the pandemic. Instead of misleading case counts, the CDC has estimated the number of cases, hospitalizations, and deaths:
- The CDC estimates that between 43 million and 89 million cases of 2009 H1N1 occurred between April 2009 and April 10, 2010. The mid-level in this range is about 61 million people infected with 2009 H1N1.
- The CDC estimates that between 195,000 and 403,000 H1N1-related hospitalizations occurred between April 2009 and April 10, 2010. The mid-level in this range is about 274,000 2009 H1N1-related hospitalizations.
- The CDC estimates that between about 8,870 and 18,300 2009 H1N1-related deaths occurred between April 2009 and April 10, 2010. The mid-level in this range is about 12,470 2009 H1N1-related deaths.
How serious is the public health threat of a swine flu epidemic?
The U.S. government declared swine flu to be a public health emergency. The World Health Organization considers it a global emergency.
As of June 2010, the WHO still considered the world to be in a flu pandemic. That inevitably will change, probably before the end of winter in the Southern Hemisphere (summer in the Northern Hemisphere).
As the pandemic winds down, the WHO will declare the world to be in a "post-peak period," meaning that the spread of flu has slowed to a trickle and that new waves of infection are possible but unlikely. Finally, the WHO will announce the "post-pandemic period," meaning that the pandemic is over and that the 2009 H1N1 virus has become a seasonal flu bug.
Despite more than 12,000 U.S. deaths in relatively young people and many more deaths worldwide, the 2009 H1N1 virus was not as bad as it could have been. The virus never incorporated virulence factors that would have made illness much worse, nor did the virus evolve into a nightmare plague. In fact, the virus remained unchanged throughout the first year of the pandemic.
WebMD senior writer Miranda Hitti contributed to this report.