Experts are still recommending a flu shot this year, because a less-effective flu vaccine can still reduce the severity of a flu illness.
This year, the H3N2 flu virus appears to have mutated — rendering the vaccine only about 10% effective, according to a study in the New England Journal of Medicine.
Flu viruses spread in the winter months, so experts in the U.S. look to the Southern Hemisphere to predict how bad our flu season will be.
Australia had a particularly bad flu season this year. The number of reported flu illness in Australia hit 215,280 by mid-October, far exceeding the 59,022 cases during the 2009 H1N1 pandemic.
Even in the best years, flu shots are only 40-60% effective at preventing the flu. Furthermore, the effectiveness of flu shots changes for people who have had previous flu shots or infections with the flu.
Another factor that may reduce the effectiveness of flu shots is how they are made. In the U.S., most flu shots contain viruses that are grown in eggs, where they mutate to better infect birds.
This would help explain why Australia’s flu season was so bad, despite widespread vaccination programs and a vaccine that was well-matched against the H3N2 strain. According to the researchers:
This possibility underscores the need to strive toward a ‘universal’ influenza vaccine that will protect against seasonal influenza drift variants as well as potential pandemic strains.”
The World Health Organization estimates that the U.S. typically sees between 140,000 and 710,000 flu-related hospitalizations and between 12,000 and 56,000 deaths from the flu every year.
People who are very young, old, or already sick have the highest risk — but anyone who gets the flu can potentially die from the illness.