Last reviewed and revised on September 2, 2009  By Anthony L. Komaroff, M.D.
Brigham and Women's Hospital Q: What is a pandemic?" 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. That is what has happened with this new swine flu virus, which contains some genes from human, swine, and bird influenza viruses. Sometimes this swapping of genes changes a virus from one able to infect only pigs or only birds to one that also can infect humans. When that happens, we refer to the illness as "swine flu" or "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. Early 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 apparently is transmitted by sneezing and coughing and by skin-to-skin contact (like shaking hands or kissing) with an infected person. It now has spread to nearly 200 countries around the world. On June 11, the World Health Organization stated that a pandemic had developed. Q: Are swine flu or bird flu viruses dangerous? A: When swine flu or bird flu viruses develop the ability to spread from human to human, they can be very dangerous: they can cause a pandemic, and they can produce severe disease. One reason that pandemic illness often is more severe than the regular winter flu is that the virus is so new. The regular winter flu viruses that circulate each year are human influenza viruses and are similar to the viruses that have caused the flu in past years. As a result, most people have some degree of immunity to the latest, regular human-flu virus. The unusual swine flu or bird flu viruses that develop the ability for person-to-person spread are so different from regular human flu viruses that many people have little or no immunity to them. That is what experts think has happened with the new swine flu H1N1 virus. Q: How contagious will this virus be? A: So far, this virus appears to be somewhat more contagious than 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. However, all flu viruses love cold weather: Cold, dry air makes flu viruses more contagious and more likely to cause serious illness. Since this new virus began infecting large numbers of people in the northern hemisphere only in the spring and summer — when air is warm and moist — it could become more contagious during the fall and winter. Q: How serious is the illness caused by this virus? A: The normal winter flu kills about 1 out of a 1,000 people who are infected with the virus. In the United States, that amounts to about 35,000 people every year. Early estimates indicate that the new swine flu virus may kill about 2 out of 1,000 people, or about twice as many as normal seasonal flu. However, there is reason to believe that it could cause more severe disease in the late fall and winter of 2009-2010. How severe can a flu virus be? The worst pandemic of flu virus on record occurred in 1918-1919. That virus killed about 3 people out of 100 people infected around the world — thirty times as many as the normal seasonal flu virus. The new swine flu virus does not have some of the characteristics of the 1918-1919 virus that made it so deadly. On the other hand, it is like the 1918-1919 virus in two respects. First, it can infect cells deeper in the lungs, producing more severe lung damage in animals. Second, it is more likely than the usual winter flu to cause serious illness in otherwise healthy young adults. In late August 2009, a Presidential panel reported that swine flu could infect half of the U.S. population in the fall and winter of 2009, and cause 1.8 million people to be hospitalized, 300,000 to require intensive care, and as many as 90,000 deaths — triple the number of deaths caused by the usual seasonal winter flu. In other words, according to these estimates, swine flu will be more severe than the usual winter flu, but not as severe as the 1918-1919 pandemic. But the truth is that it is very difficult to predict what will happen with flu viruses because they can change their genes so rapidly. Q: How do I know if I've caught swine flu? 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. If this epidemic hits your community and you develop flulike symptoms, it is likely your doctor will take samples from your throat or material you cough up for testing. Q: How do I protect myself? A: To protect yourself from catching swine flu: - 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.
Q: How do I protect others if I get sick? A: If you develop symptoms that could be swine flu, like those mentioned just above, and if your local health department says there is an epidemic in your community, you should pay close attention to your health department's specific advice. But in general: - If you are coughing and sneezing, stay at home!
- And at home, try to stay away from others as much as possible. If you can, try to stay in one room (and have others avoid that room). If you have more than one bathroom and it is practical to do so, choose one bathroom you can use and let everyone else in the household use another.
- If you are coughing and sneezing, don't sneeze into your hands. Instead use tissue and deposit the tissue in a wastebasket or toilet. Wash your hands immediately after. If you use a handkerchief, the person putting it in the washing machine should be sure to wash his or her hands immediately after.
- Don't shake hands with people, or kiss "hello."
- If you have to go out, avoid crowded situations like public transportation and movie theaters.
Q: How long are people contagious? 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. Q: I hear the virus seems to be losing its punch. Is that true? Probably not. The virus did seem to produce more severe disease in Mexico than in the United States and most other parts of the world. But that could be because the weather was getting warmer, and because people in Mexico — not knowing the danger — waited longer to seek medical help. As explained earlier, many experts worry that the virus could produce more severe disease as it spreads in the cold, dry air of fall and winter. That has happened with past pandemics: A summer reprieve was followed by a major outbreak in the fall and winter. Also, influenza viruses change their genes so frequently that the nature of epidemics can change quickly as well. The genetic changes could make the virus cause either more or less serious illness. Q: Who gets swine flu? 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. Q: Are there treatments? A: As of now, the new 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. As long as this current swine flu virus is infecting people, it is likely that health authorities will recommend that people with more severe illness take these medicines. On the other hand, there is no proven benefit from using the medicines before symptoms develop, and there is proven harm: Unnecessary widespread use of these drugs could produce drug-resistant viruses. Q: What about vaccines? A: Many pharmaceutical companies around the world are hard at work manufacturing a vaccine. It is too early to know how effective the vaccine will be, how safe it will be, and how much of it will be available by the late fall and winter of 2009-2010. It appears that the first doses of the vaccine will be available in late October 2009. Almost certainly, at first there will not be enough vaccine for everyone. In the United States certain groups will get the highest priority: - Pregnant women because they are at higher risk of complications and can potentially provide protection to infants who cannot be vaccinated.
- Household contacts and caregivers for children younger than 6 months of age because younger infants are at higher risk of influenza-related complications and cannot be vaccinated. Vaccination of those in close contact with infants less than 6 months old might help protect infants by "cocooning" them from the virus.
- Health care and emergency medical services personnel because infections among health care workers have been reported and this can be a potential source of infection for vulnerable patients. Also, increased absenteeism in this population could reduce health care system capacity.
- Children 6 months through 4 years of age, because they are at higher risk of complications
- Children 5 through 18 years of age who have chronic medical conditions, because they are at higher risk of complications.
If the vaccine supply is more plentiful, then the CDC recommends vaccinating these same groups plus: - Anyone 5 years through 24 years of age
- Children from 6 months through 18 years of age because many cases of novel H1N1 influenza occur in children and because children are in close contact with each other in school and day care settings, which increases the likelihood of disease spread
- Young adults 19 through 24 years of age because many cases of novel H1N1 influenza occur in these healthy young adults, because they often live, work, and study in close proximity, and because they are a mobile population
- People 25 through 64 years of age who have health conditions associated with higher risk of medical complications from influenza.
Once these people have been vaccinated, then everyone from the ages of 25 through 64 years can begin to be vaccinated. Research shows that the risk for infection among persons age 65 or older is less than the risk for younger age groups, probably because healthy people in this older age group are more likely to have some degree of immunity against the virus. Q: Can you get swine flu from eating pork? 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. Q: Will there be unusual restrictions on our lives if there is a global pandemic? A: If a global pandemic becomes serious enough, for some period of time governments may well restrict travel. Governments also may close schools and public places, require as many people as possible to work from home, tell any people who develop symptoms to isolate themselves at home, and tell people to seek medical attention immediately if more serious symptoms develop. What are those symptoms? For adults, teens and children 3 to 12 years of age, the most worrisome symptoms are: - Shortness of breath
- Persistent vomiting
- Confusion
- Dizziness
For children younger than 2 years, the most worrisome symptoms are: - Very rapid breathing
- Not interacting normally, not eating or drinking normally, being unusually irritable, or appearing unusually sleepy
- High fever and rash
- A bluish color to the lips and skin
For more information on swine flu and influenza, go to Harvard Medical School's Flu Resource Center. Back to top Anthony L. Komaroff, M.D. is the Simcox-Clifford-Higby professor of medicine and editor-in-chief of Harvard Health Publications at Harvard Medical School. Dr. Komaroff also is senior physician and was formerly director of the Division of General Medicine at Brigham and Women's Hospital. Dr. Komaroff has served on various advisory committees to the federal government, and is an elected Fellow of the American Association for the Advancement of Science.
| 
