A mismatch between the influenza vaccine and circulating strains of the virus in Australia has health officials in the United States concerned that we may be in for a worse-than-usual flu season here too.
A recent article in the New England Journal of Medicine reported that as of mid-October, Australia had a reported 215,280 influenza cases during the 2017 flu season (Australia’s season typically runs from April to September each year—which is winter in the Southern Hemisphere). That number far exceeds the country’s previous record, set in 2015, in which more than 100,000 people tested positive for the flu. And since only a fraction of people with influenza are tested, the numbers reported are generally far lower than the actual number of cases.
An apparent mismatch between the influenza strains used in this season’s vaccine and the strains that actually circulated in the community appears to be a major culprit. Indeed, according to the article, Australia’s Department of Health determined that this year’s vaccine was only about 10 percent effective against the particular subtype of influenza A (H3N2) that primarily circulated in the country this year.
Researchers believe that the mismatch between the vaccine and the circulating strain may have to do with the way in which the flu vaccine is created. The influenza vaccine is produced using an egg-based production process. During the process, the vaccine virus acquires certain structural changes that allow it to replicate in the eggs. However, these changes also can cause changes in the vaccine virus, altering it from its original composition and thereby making it less effective against the circulating virus.
An imperfect vaccine
This isn’t the first time a vaccine mismatch has led to a larger-than-usual outbreak of influenza. Because the flu virus constantly changes, each year the flu vaccine is modified, as needed, to match the strains observed around the world in the preceding year. This is part of the reason we all need a new flu vaccine each year (another reason is that the protection from the vaccine tends to last only about six months in most people). But scientists can’t predict for certain that the strains that circulated in the preceding year will be the dominant ones the next year. And even when the vaccine and circulating strains are a good match, the influenza vaccine is not as effective as many other vaccines. This may be due to the fluctuating nature of the virus, the method of creating the vaccine (using an egg-based substrate in which the virus can sometimes become altered, as discussed above), and even an individual’s previous exposure to certain strains of influenza. For this reason, researchers are trying to develop a “universal” flu vaccine that would protect against a greater variety of strains, including variants that may emerge after the vaccine for a given year is developed.
What to do
Everyone should get an annual flu shot: While it’s not perfect, the vaccine is your best defense against the illness.Influenza can be a serious—sometimes fatal—disease, causing complications such as severe pneumonia that can result in hospitalization or even death. The virus can also lead to inflammation of the heart, brain, and muscle tissues; in severe cases, it can cause multi-organ failure. Young children, adults over age 65, and people with chronic medical conditions are at especially high risk of serious flu complications. The CDC estimates that the influenza vaccine averted 40,000 deaths over a nine-year period (2005-2006 season to 2013-2014 season). But the potential for a mismatch between this year’s shot and the strains that will circulate highlight the importance of other infection-prevention measures you should take throughout cold and flu season.
Also see Cold or Flu? Comparing the Symptoms.