Adults ages 18 through 49 get a flu shot at much lower rates than others. If you're thinking that a flu shot won't really help you, because you've heard it's only 30 percent effective, think again. There are many strains of flu, and the shot can protect you against three or four of them. The 30 percent figure applies only to the dominant strain this year -- your shot might protect you from completely different strains.
It’s possible, for example, that later in the flu season influenza B could become active -- that's a strain that the current vaccine is effective against, says Dr. Richard Webby, a member of the Department of Infectious diseases at St. Jude Children’s Research Hospital, and of the World Health Organization team that formulates the flu vaccine.
Also, it isn't just about you, points out Aaron E. Carroll, a professor of pediatrics at Indiana School of Medicine, in a recent New York Times post.
"You don’t get immunized just to protect yourself," Carroll writes. "You also get immunized to protect those who can’t protect themselves."
That means people like babies who are too young to get the shots and people with compromised immune systems.
Carroll says in the 2015 to 2016 season, flu shots prevented an estimated 3,000 deaths. Yet, in that same season:
"If just 5 percent more people had been immunized, we could have probably avoided 500,000 illnesses, 230,000 medical visits and 6,000 hospitalizations … Less than 50 percent of children are immunized against the flu. About two-thirds of people 65 and older are. But only a third of adults 18 to 49 are."
Why the Vaccine Isn't Perfect
Currently, flu cases are dominated by a strain of influenza A called H3N2. And the problem this year is not that the WHO scientists got the strains wrong in the vaccine -- H3N2 is covered by the flu shot.
The problem is that the virus changes during the production of the vaccine.
Twice a year, WHO scientists meet to develop a flu vaccine: once for the world’s northern hemisphere and once for the southern. They do this about six months before the flu hits a given hemisphere, and they choose which viruses to include based on disease trends identified from laboratories worldwide.
Next, the viruses get injected into chicken eggs.
“Sometimes the flu virus doesn’t like to grow in eggs that much,” Webby says. So it mutates to adapt to its new home.
The result is that the lab-grown H3N2 used in this season’s flu shot doesn’t quite match the H3N2 currently being spread in people.
“We're really having a few difficulties getting the perfect match between these H3N2 viruses and the vaccine,” Webby says.
He adds that in the future, there are some ways scientists could improve the vaccine. It could be grown in a different medium instead of eggs, for example, to prevent the virus from mutating as much.
Meanwhile, Webby says flu activity this year could continue to increase.
“We’re not sure we’ve seen the peak of flu season yet.”