USciences Professor of Virology Talks About Flu Season Safety

By Nicole Carrera

Published on September 30, 2021

Taisuke Izumi, PhDAs flu season approaches, Assistant Professor of BiologyTaisuke Izumi, PhD, shared more about the flu, who is at risk, and why it’s important to get the annual flu vaccine.

How dangerous is the flu? Who is most at risk?
Though most people infected with the flu recover in a few days to less than a couple of weeks, some develop complications such as inflammation of the heart, brain, muscle tissue, or multiorgan failure triggered by the flu infection or coinfection with other infectious agents. Anyone, even healthy people, has the risk of getting sick and severe problems related to the flu at any age. However, those over the age of 65, under the age of 5, pregnant women, and those who are immunocompromised are at a high risk of developing flu-related severe illness.

How does the flu shot work?
Flu vaccines dominantly introduce antibodies approximately two weeks post-vaccination, which protect against the circulating flu infection. Researchers predict which strain of flu will be dominant in the upcoming season and design seasonal vaccines.

Flu vaccines are quadrivalent in the United States, which means that they stimulate an immune response against four different antigens. They are designed to protect against four different flu viruses: influenza A (H1N1, H3N2) and two different lineages of the most circulating influenza B viruses.

Why is it important to get a flu shot each year?
The dominant circulating flu viruses are changed in each season. Therefore, the CDC predicts which strains will most likely occur the year before each flu season and design the optimized flu vaccines. In addition, immune protection efficacy induced by flu vaccines is short-lived and declines over time. The protection efficiency falls back to the starting point in one year.

Who should get a flu shot?
Everyone older than six months should get a flu vaccine every season. Vaccination is essential, especially for people at a higher risk of developing severe flu complications as described above, with rare exceptions such as children younger than six months and people who have had, or potentially have, severe life-threatening allergies to any ingredient in the flu vaccine.  

Can you get the flu from the flu shot?
No, flu vaccines cannot cause flu illness. Flu vaccines are made with either inactivated viruses or attenuated viruses that will not cause illness.

There are several reasons why vaccinated people might get the flu and get sick with flu symptoms. It is possible to be exposed to flu viruses shortly before getting vaccinated and before the period of immune activation, approximately two weeks.

However, even when people with vaccines were infected with the flu virus, several studies showed that flu vaccination was associated with a 21% - 59% lower risk of ICU admission and a 31% lower risk of flu-related fatality.

What are common side effects of the flu shot?
Common side effects are soreness, redness, and swelling at the injection site. It occasionally causes headaches, fever, nausea, muscle aches, and fatigue.  

What should people know about the flu shot and the COVID-19 vaccine?
There is no evidence that getting a flu vaccination increases the risk of getting sick from a coronavirus like SARS-CoV2 that causes COVID-19.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, announced that it is safe to get a coronavirus vaccine or vaccine booster shot at the same time with the flu shot.

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