Press Release

FSU Expert Available to Comment on Effectiveness of Flu Vaccine

CONTACT: Bill Wellock, University Communications
(850) 645-1504;
February 2020
TALLAHASSEE, Fla. — As an outbreak of a new coronavirus makes headlines across the world, another more common infectious disease is spreading across the United States and beyond — the flu.
About 8 percent of the U.S. population gets sick from the flu each season, according to the Centers for Disease Control and Prevention. Although anyone can get sick, people 65 years and older, children younger than 5, pregnant women and people with medical conditions are at greater risk of serious complications.
Dr. Christie Alexander, an associate professor at the Florida State University College of Medicine and president of the Florida Academy of Family Physicians, is available to explain how scientists develop each year’s flu vaccine, why its effectiveness varies and whether it’s still worth getting a flu shot in February.
How does the development process for each year’s flu vaccine work?
Development starts right around the end of the previous year’s flu season, and it’s based on that year’s flu season. Scientists try to develop the vaccine based on that season, looking back to see what the rates of the various flu strains were and then developing the flu vaccine according to that, trying to anticipate what the next flu season will look like.
Can you talk about the different strains?
There’s influenza A and influenza B. The flu shot is trying to prevent against two strains of A and two strains of B. Those strains mutate every year, so scientists try to target the mutations as best they can and create the vaccine based on what those strains looked like that year.
Why is the vaccine sometimes more or less effective?
This is because the strains mutate so quickly and so readily. Even after scientists develop the shot and we start to administer it, those strains can change again. Once the flu shot is developed, you can’t recreate it, so the hope is that scientists are able to correctly predict any possible mutations for the next year in order to gain the most protection from the shot.
Some experts have said there may be a “mismatch” between the vaccine and the strains this year. What does that mean?
That gets back to mutation. We have the two strains of influenza A and the two strains of influenza B, and if one of those four strains starts to mutate, then the shot will no longer match the strains. So it might hit three of the four really well, but if the fourth starts to mutate, you’ll see a resurgence from that strain. That’s what the term “mismatch” means. It doesn’t happen every year. In fact, over time, the shot has been 40 to 60 percent effective, which translates into the prevention of literally millions of illnesses and flu-related doctor’s visits each year. For example, based on information from the CDC, during the 2017-2018 flu season, the vaccination prevented an estimated 6.2 million influenza illnesses, 3.2 million influenza-associated medical visits, 91,000 influenza-associated hospitalizations and 5,700 influenza-associated deaths.
How effective is this year’s vaccine?

We can’t know final numbers until flu season is over because the numbers include how many people got the shot, how many cases of the flu we saw, which strains of the flu they were, how many people were hospitalized — those types of things. Right now, it looks like it is on track with previous years, but it’s hard to say. The most recent data from the CDC shows most cases are influenza B this year, but this alone does not predict how effective the shot has been.
Right now, it’s February. Should you still get a flu shot if you haven’t gotten one?
Absolutely. The flu season usually goes from October all the way through April, sometimes even May. We see a bimodal uptick with a rise in cases in December and a rise in cases in February. Therefore, we recommend continuing to get the flu shot to not only avoid getting the flu, but to avoid complications from the flu, such as hospitalizations, influenza-associated illnesses like pneumonia or even death. So the short answer is, “Yes! Get your flu shot!”