When to Get a Flu Shot in 2021


Syringes of influenza vaccine about to be used at a free vaccine drive last year in Los Angeles.

Syringes of influenza vaccine about to be used at a free vaccine drive last year in Los Angeles.
Photo: Damian Dovarganes (AP)

The dog days of summer are just about coming to the end in the U.S. And while the fall may mean cool breezes and nice walks in the park, it should also mark the arrival of the annual flu shot or spray. Getting vaccinated against the flu remains one of the simplest and best things you can do for your health, especially in a world where covid-19 is unfortunately still around. This year, it’s probably best to get an influenza vaccine sooner than later.

Typically, the flu season runs from October to March, with the peak around January or February. But there are some important considerations that could make the upcoming season we face more intense and more unpredictable than usual.

For one, the flu was virtually non-existent last winter, possibly aided by a higher vaccine uptake as well as the measures people took to limit the spread of covid-19, such as avoiding gatherings and wearing masks in public (covid-19 vaccines arrived by mid-December but weren’t widely available until March 2021). This reprieve may have reduced the number of different flu strains circulating in the world. But it could also mean that there is some reduced flu immunity in the community, the Centers for Disease Control and Prevention has warned. The flu mutates so quickly that we never have complete immunity to it, but our preexisting experience with a returning flu strain can temper the harm it causes. So people who aren’t vaccinated and whose immunity has waned could face a higher risk of infection and serious illness.

Available as both a nasal spray and shot for most everyone six months and older, the flu vaccines will protect against four circulating strains of influenza. Because it takes two weeks for the immunity to kick in, getting it as early as September is usually recommended anyway, and you should try to get it at least before the end of October. But because the situation is in flux this year, scheduling the shot as soon as possible in September may be even better.

Unlike last year, there will be less focus on social distancing measures to contain the ongoing pandemic, given that many people are now vaccinated against covid-19. Notably, the Biden administration has explicitly said that it will not push for the sort of restrictions on movement seen last year, hoping that mask use and vaccination will be enough to keep the coronavirus in check. This relaxed environment will no doubt allow the flu to spread more easily and perhaps sooner than normal, since other seasonal respiratory viruses that laid dormant last year have returned at unexpected times.

Experts were worried about the dual threat of covid-19 and flu last winter, a prediction that didn’t come to pass because the flu just wasn’t around (unfortunately, our measures weren’t enough to stop the deadliest peak of covid-19, a disease that is apparently more contagious than the flu). But for people who aren’t strongly protected against both this year, which can include children not able to get vaccinated for covid-19 and the immunocompromised who don’t respond as well to vaccines, this threat looks to be very real now.

Because of the fast-evolving nature of the flu, our seasonal vaccines usually aren’t highly effective at preventing illness from it. And they can sometimes be very mediocre, due to a big mismatch between the strain included in the vaccine and a circulating strain that’s mutated to be less recognizable to the trained immune system by the time the season starts. But even in a down year, flu vaccines prevent millions of cases, tens of thousands of hospitalizations, and thousands of deaths in the U.S. annually, and they would do even more if more people took them (typically, around half of all Americans get flu shots). This protection also reduces transmission in the community, which may keep some unprotected people from getting sick as well. So far, according to the CDC, there’s no indication that this year’s batch of vaccines will be badly mismatched.

Covid-19 may be worse than the flu, but as anyone’s who experienced it well knows, the flu will make you seriously miserable. So get the shot or spray this fall or winter, and significantly lower your risk of getting sick over the coming months.