On Dec. 4, 2014, the CDC issued a health advisory stating that some of the predominant flu strains circulating so far this season appear to differ from those the vaccine was designed for—raising concerns (and a flurry of media reports) that this year’s flu shot won’t provide adequate protection. But the reality is less dire. Here’s what the CDC’s report really means and what you can do to minimize your risk of getting sick.
What the numbers mean
The CDC advisory contained information about what the currentinfluenza season may have in store, based on the relatively light flu activity in the U.S. so far. The predominant strains currently circulating are called H3N2; preliminary data suggest that about half of these strains differ somewhat from the vaccine being used. In infectious disease language, this is known as “drifting”; that is, the strains being detected have drifted away from the strain used in the vaccine.
This is disturbing for two reasons. First, H3N2 strains tend to cause more hospitalizations and deaths than other strains, such as H1N1 (swine flu) and influenza B. And the vaccine is likely to be less effective against strains that have drifted.
At the same time, interpreting these numbers merits caution. Influenza activity has been relatively light to date, with only 1,228 cases reported to the CDC. Of the virus samples taken from those patients, only 81 were tested, 44 of which had drifted away from the vaccine strain. We don’t have information about the other 1000-plus strains.
What’s more, we know from past flu seasons that even in strains that have drifted, vaccination may still make illness milder and prevent influenza-related complications such as pneumonia. So that flu shot you got (or should still get, if you haven’t already) wasn’t for naught.
How to protect yourself
Regardless of what happens during this flu season, there are three important take-home messages:
1. Be sure to get vaccinated against influenza. It’s our first line of defense. Even if the vaccine is only 50 percent effective against H3N2, that's still significant protection. If you don’t get sick, you’re unlikely to spread the flu to others. And the other components in this year’s vaccine should still be effective in preventing other strains, including H1N1 and influenza B. (H3N2 is a form of influenza A.) It’s not too late to get vaccinated, but do it soon, since it takes about two weeks after the vaccine to be protected.
2. Know the symptoms of flu and be on the lookout for them. The trademark signs are high fever, severe body aches, and a terrible cough. Vomiting and other gastrointestinal symptoms, sometimes inaccurately referred to as “stomach flu,” are actually NOT symptoms of influenza except in children.
3. If you develop flu symptoms, tell your health care provider ASAP. Two antiviral drugs—oseltamivir (Tamiflu and generic versions) and zanamivir (Relenza)—are effective at reducing the severity and preventing flu-related complications, especially if started within 48 hours of symptoms. This is most important for people at higher risk for severe illness, including children age 2 or younger and adults age 65 or older; pregnant women; people who are obese or have underlying diseases such as diabetes, heart problems, or chronic lung disease (including asthma); people with weakened immunity; residents of nursing homes and other long-term care facilities; and American Indians/Alaskan Natives. Starting antiviral drugs right away also shortens the amount of time you’re contagious, which may reduce the chance that you’ll spread the illness to others.