Last reviewed and revised on March 23, 2012
By Anthony L. Komaroff, M.D. Q: What is a pandemic?"
Brigham and Women's Hospital
An epidemic is an illness that spreads to many people, and a pandemic is an epidemic that spreads around the world. When the words "epidemic" and "pandemic" are used, they often refer to a spreading infection caused by viruses or bacteria. However, pandemics can refer to non-infectious illnesses, such as the obesity epidemic caused by unhealthy lifestyles.
Pandemics typically are caused by a new type of infectious agent to which most people have not yet developed immunity. Pandemics often cause more severe disease than epidemics but not always.
Q: What is "swine flu?"
A: Flu is a disease caused by the influenza virus. Humans, pigs, birds and other animals can be infected by influenza viruses. Typically, influenza viruses can infect only one species, so the influenza viruses of humans are different from those of pigs and birds.
However, sometimes a virus can infect more than one species. For example, pigs sometimes can be infected not only with pig influenza viruses, but also with human and bird influenza viruses. Then these viruses can swap genes, creating new viruses that have a mix of genes from human, pig and bird viruses.
Sometimes this swapping of genes changes a virus from one able to infect only pigs to one that also can infect humans. When that happens, we refer to the illness as "swine flu." (When a virus that normally infects only birds develops the ability to infect humans, we refer to the illness as "bird flu.") When a swine (or bird) influenza virus develops the ability to infect a human, it usually is not easily passed from human to human, and so an epidemic caused by the virus does not develop.
However, in 2009, a new swine flu virus emerged in Mexico that not only developed the ability to infect humans, but also the ability to spread easily from human to human. It contains some genes from human, swine, and bird influenza viruses. This virus still is circulating around the world, and many (perhaps most) people have been exposed to it. Other swine flu viruses have affected humans in the past.
In these questions and answers, we are always referring to what is called the "2009 H1N1" swine flu virus, not to other past swine flu viruses.
Like other flu viruses, 2009 H1N1 is transmitted by sneezing and coughing and by skin-to-skin contact (like shaking hands or kissing) with an infected person. Within a few months in 2009 it had spread to nearly 200 countries around the world. in June 2009 the World Health Organization stated that a pandemic had developed.
Q: Is the 2009 H1N1 flu virus dangerous?
A: At first, experts were very concerned that the 2009 swine flu virus might be quite dangerous because it was a brand new virus. But the virus was similar enough to flu viruses that were present many decades ago that people over age 50 had pretty good immunity to it. This is the group that usually is hit the hardest by flu viruses. But people over age 50 actually had milder illnesses than with the usual winter flu viruses.
However, younger adults (particularly pregnant women) and children were hit a lot harder by the 2009 swine flu virus than they are by the usual winter flu viruses, because they had little, if any, immunity to it.
Q: How contagious is the 2009 H1N1 virus?
A: The 2009 H1N1 virus appears to be as contagious as the usual seasonal human flu virus. About a quarter of people who have had close exposure to someone with swine flu have gotten the virus. Over time, as many as half of the people of the world may have been exposed to the virus.
Q: Can people die from the 2009 H1N1 virus?
A: Unfortunately, the answer is yes. Even the typical seasonal flu viruses kill about 1 out of a 1,000 people who are infected. In the United States, that amounts to about 35,000 people every year. Fortunately, the 2009 H1N1 virus has proved to be less likely to cause death in older people. Unfortunately, it has proved more likely to cause death in young, pregnant women and children.
Q: How do I know if I've caught the 2009 H1N1 virus?
A: The initial symptoms of this flu virus are like those of the regular flu: fever, muscle aches, runny nose and sore throat. Nausea, vomiting and diarrhea may be more common with this swine flu than with the regular flu.
Q: How do I protect myself?
A: To protect yourself from catching any kind of flu virus or many other infectious microbes:
- Wash your hands or use alcohol-based hand cleaners frequently. For a thorough hand washing, use soap and scrub all parts of your hands front and back, and between your fingers for about 20 seconds (about as long as it takes to sing "Happy Birthday").
- Don't touch your hands to any part of your face. If the virus is on your hands, it can spread to your throat and lungs from your nose and mouth, or even your eyes.
- When you greet people, don't shake hands or exchange kisses. Instead, bump elbows, wave or just say "Hi."
- Avoid contact with people who are sneezing or coughing. To the extent you can do so, avoid crowded situations. Stay at least three feet away from others.
- If you are in public places, remember that when your hands touch what other people's hands have touched, the virus could be passed to you. For example:
- On a bus, don't hold on to an overhead strap or to a pole. Instead, wrap your arm around the pole to support yourself.
- When climbing stairs don't hold on to the railing unless you absolutely have to.
A: Adults should be considered contagious until at least 7 days after the start of symptoms; with children, it may be 10 to 14 days.
Any person of any age can catch any kind of influenza. With the regular yearly influenza, young children and older adults are most vulnerable, particularly to more severe illness.
A: The 2009 H1N1 virus is killed by two antiviral medicines: oseltamivir and zanamivir. Based on experience with other flu viruses, treatment would be most effective if given within two days of the onset of symptoms. These medicines should be reserved for those with more severe symptoms, particularly if they are children.
A: A vaccine was developed for the 2009 H1N1 virus; many people were immunized. In fact, since the virus has continued in circulation around the world since 2009, the regular seasonal flu vaccines given since 2009 cover the 2009 H1N1 virus.
A: Absolutely not. But, as you probably know, you need to cook pork thoroughly to avoid getting other illnesses that can be spread by undercooked meat.
For more information on swine flu and influenza, go to Harvard Medical School's Flu Resource Center.