Facts About Swine Flu

Shannon Brownlee and Jeanne Lenzer, the authors of the November 2009 story "Does the Vaccine Matter?", answer questions about H1N1 diagnosis and immunity.

Q: How can I tell if my symptoms are from the flu or a cold?

A: In short, you can’t. At least not with any degree of certainty. And neither can doctors. According to a review by Dr. Tom Jefferson [PDF], head of the flu vaccine section of the respected Cochrane Collaboration, when doctors determine that a patient’s symptoms are consistent with flu, they are wrong on average over 90% of the time. Other studies fix the number at half of the time. That’s because the common cold and other viruses cause symptoms that are often indistinguishable from the flu despite the common wisdom that flu patients are more likely to experience generalized muscle aches and pains, headaches, and fever along with a cough and runny nose.

Q: If symptoms aren’t reliable indicators, how can my doctor tell if I have swine flu?

A: The only way to make a definite diagnosis of the 2009 H1N1 flu (previously known as swine flu) is to do a nasal swab or blood tests. The rapid tests are highly inaccurate; for example the rapid influenza detection test (RIDT) is completed in 30 minutes but only picks up 10-70% of influenza A viruses and can’t distinguish between swine flu and other types of influenza A viruses. Viral cultures or RNA amplification tests are more accurate but take from 2 to 10 days to get results, making them irrelevant for decision-making regarding antiviral drugs, for example, which are supposed to be started within 36 hours of the onset of symptoms. The Centers for Disease Control and Prevention currently recommends testing only in limited circumstances.

Q: What is the difference between the seasonal flu vaccine and the swine flu vaccine?

A: Each year, experts review the viruses that caused flu that season and they select three of those viruses to create the following year’s flu shot. The 2009 seasonal flu vaccine does not include swine flu virus. The swine flu vaccine contains only a single virus: the 2009 H1N1 virus. The CDC recommends that most people receive both the seasonal flu and the 2009 H1N1 vaccines. This year’s seasonal flu vaccine is expected to be protective against less than 1% of flu cases since over 99% of flu currently is due to the 2009 H1N1 virus.

Q: What’s known about the risks of flu shots?

A: Risks are considered by most experts to be very low and limited largely to local pain and swelling at the site of injection with rare instances (1 in 1 million) of a paralyzing condition known as Guillian-Barre Syndrome (that rate was higher during the previous swine flu outbreak in 1976 when the incidence was estimated at 1 in 100,000). According to the CDC, none of the shots approved for use in the U.S. will contain adjuvants (substances that enhance immune reactions) such as squalene. Vaccines containing adjuvants have been approved in Europe. However, injected flu vaccines may contain thimerosal, a mercury-containing preservative, which many doctors believe is safe but others believe may be responsible for effects on the brain and nervous system. For people who want to take the vaccine but avoid the mercury, they can ask for single-dose vaccines.

Q: I’m confused. We’re told not to rush to the doctor or hospital if we have symptoms of flu because we might spread infection, and at the same time we’re told that if we need antiviral drugs for flu that we have to be seen at the onset of symptoms in order to be effectively treated. What should I do if I have flu symptoms?

A: The best thing to do is to call your primary care doctor for advice rather than going to an emergency department since much depends on your personal risk factors. If you have any unusual symptoms, such as shortness of breath, wheezing, or difficulty taking fluids, you should seek immediate help.

Q: How dangerous is swine flu?

A: At this point, it is proving to be relatively mild and less fatal than the average flu, according to data from some countries in the Southern Hemisphere that already experienced their winter flu season. Unless the virus mutates, it appears that the most serious threat is largely to people with underlying health problems.

Q: I see studies that say the flu vaccine is highly effective. Why is there any question?

A: Effectiveness is often measured by showing that people who get the vaccine develop antibodies in response to the vaccine. Those antibodies can be helpful in fighting off future bouts of that year’s flu. The problem is that young, healthy people are very good at developing antibodies but they are not the people who tend to develop pneumonia or die, while older people and people with immune disorders, who are most likely to die, don’t develop protective antibodies as well. This has led to the question, “Is it necessary for those whom it helps, and will it help those for whom it’s necessary?”

Q: Isn’t vaccination helpful for “herd immunity”—to protect the elderly and those with immune deficiency—from exposure to flu?

A: One of the most compelling arguments for flu vaccination is to provide herd immunity. In other words, by keeping young healthy people from getting sick it is believed that we can slow the spread of the disease to others. That could help to protect those who can’t benefit from a vaccine due to a weak immune system. Studies in nursing homes suggest that there is benefit to the elderly when caretakers are immunized along with residents. The current recommendation to give annual flu shots to infants and children, however, has not been tested to ensure that the strategy is safe in the long term for children and that it actually confers benefit to the elderly. Focused strategies of immunizing those in close contact with the elderly and those who are immune compromised are fairly widely endorsed and may be helpful.