Mid-September through October is the sweet spot for getting a flu vaccine, but it's almost never too late to get your jab.

Advertisement

Last flu season saw the lowest number of cases in the US of any flu season on record—just over 2000, per government data cited by JAMA. In some ways we have the COVID-19 pandemic to thank for that. Without a vaccine available against COVID, people were careful to protect themselves by wearing masks, washing their hands, and practicing social distancing. Those measures are powerful against all respiratory illnesses, including COVID, influenza, and the common cold.

But before COVID stole the headlines, influenza was considered one of the deadliest respiratory diseases in the US. During the 2019-2020 flu season—the one right before the pandemic—an estimated 38 million Americans were infected with influenza, and 22,000 died, reports the US Centers for Disease Control and Prevention (CDC).

Which brings us to the 2021-2022 flu season. There's concern that this year may see a resurgence of flu. Schools are now in-person, and bars, restaurants, theaters, and concert halls are welcoming people indoors. With all this human interaction and the holiday season approaching, there's a real risk of the medical system being overwhelmed by large numbers of both COVID and influenza cases—the dreaded twindemic.

"As flu and COVID-19 compete for the same hospital resources, personal protective equipment, and diagnostic reagents, it's important to try and minimize the impact of the flu," infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, previously told Health.

Fortunately there's an effective way to do that: Get a flu vaccine. The CDC recommends that everyone six months of age and older get a flu shot every year, with just a few rare exceptions, including immunocompromised people; people who have severe, life-threatening allergies to the flu vaccine or any ingredient in the vaccine; and people who've had a serious reaction to the flu vaccine in the past.

"We want to have as many people get flu shots as possible, however, it's important to make sure that you get the flu shot when it's going to be most effective," says Dr. Adalja. Here's what you need to know to get the flu shot at the right time to make sure you're protected this season.

when to get flu shot , Close-up hands,nurses are vaccinations to patients using the syringe.Doctor vaccinating women in hospital.Are treated by the use of sterile injectable upper arm. injection
Credit: Adobe Stock

When should I get the flu shot?

If you're reading this in September or October, terrific: experts say this is the perfect time to get a flu shot, and everyone should aim to be vaccinated by the end of October. That time frame allows the body to mount enough protection against the virus before flu season becomes active. It also ensures lasting protection throughout the most active parts of the flu season. "It takes around two weeks after vaccination for enough antibodies to form and to achieve full immunity," epidemiologist Supriya Narasimhan, MD, chief of the infectious disease department at Santa Clara Valley Medical Center in California, previously told Health.

But if you're reading this in November or even December or January, it's not too late, says the CDC. Flu activity in the US usually starts in October and peaks between December and February but can sometimes continue into May, the agency notes. Don't skip the vaccine this year just because October has come and gone.

How soon is too soon to get a flu shot?

It is possible, though, to get the flu vaccine too early. You may hear in the late summer, for instance, that your local pharmacy has started offering flu shots. Resist the urge to get one immediately. By waiting until September or October you'll make sure you benefit from all the protection a flu vaccine can offer, when you may need it most.

The general consensus, according to the CDC and infectious diseases experts, is that you should generally not get vaccinated earlier than September, because the protection against the flu virus wanes over time. The flu shot is most effective in the first three months after a vaccination, but people still have protection for at least six months after the shot.

The sweet spot for getting vaccinated—mid-September to October—is to make sure that the shot protects for as much of the active flu season as possible. This advice is especially important for adults age 65 and older, since they're more at risk if their protection decreases too much before flu activity has ended for the season.

When to get the flu vaccine if you're pregnant

The short answer is: the same time as everyone else. The flu vaccine is safe throughout pregnancy, so there's no need to wait until after the first trimester to get the shot. In fact, flu vaccines are especially important during pregnancy.

"When pregnant women get the flu they're more likely to have severe disease with complications," William Schaffner, MD, medical director of the National Foundation for Infectious Diseases and professor of preventive medicine and infectious diseases at Vanderbilt University School of Medicine, tells Health.

He explains that during pregnancy parts of the immune system are suppressed, and the flu virus can cause more serious illness. Another important reason for pregnant women to get the flu vaccine is that some of the protection against influenza conferred on the mother goes across the placenta into the developing baby. After birth, the baby is protected from flu for the first six months of life, before little ones are eligible to receive their own flu vaccines.

One exception to the general flu vaccine timing rule, according to the CDC, is that pregnant women in their third trimester of pregnancy should consider getting the vaccine early—for example, in July or August—so that there's enough time for them to develop immunity before their babies are born.

Finally, while pregnant women can and should get the flu vaccine at any time in their pregnancy, they should not get the nasal spray version of the vaccine, says Dr. Schaffner. Unlike the injectables, the nasal spray is a live attenuated vaccine, meaning that the virus is weakened, not killed. The nasal spray vaccine can't cause the flu, because the virus is specially engineered to die after it's fully inhaled (and after it sparks an immune reaction while in the nose), he explains. But as the CDC points out, its side effects—nasal congestion, fever, and body aches—can be similar to the flu.

Should I wait to get a flu shot if I'm getting a COVID vaccine or booster?

There's no need to choose. Not only should you be vaccinated against both COVID and influenza, but you can even get the shots on the same day if you like.

When the COVID vaccines first became available, people were advised not to get any other vaccines for at least two weeks afterwards. That was because the COVID shots were so new that it was important to keep track of what side effects they were causing.

But the COVID vaccine has proved to be extraordinarily safe, and experts now say that it's fine to get other vaccines at the same time or soon afterwards. In fact, in September, two major pharmaceutical companies—Novavax and Moderna—announced that they were developing combined COVID booster and flu vaccine shots. The new combos, though, won't be available in time for this flu season.

Experts advise that if you do get a COVID shot and a flu shot on the same day that you don't have them both in the same arm to minimize soreness.

Morning, noon, or night: What's the best time of day to get a flu shot?

A study from the University of Birmingham in England seemed to indicate that there was some advantage to getting the flu vaccine in the morning. The study, published in 2016 in the journal Vaccine, involved adults over 65, and it found a slight advantage in the immune response that was generated when the vaccine was given before noon rather than the afternoon. But the advantage was small and only seen for two of the three strains of the flu virus in that year's vaccine (those strains change every year).

So while the study suggests that there might be a small advantage to getting the vaccine earlier in the day, doctors say what's more important is getting the shot in time to protect you for this year's flu season. If you're not a morning person, get the vaccine in the afternoon. Just make sure you go and get the shot (or spray) at whatever time of day is most convenient for you.

"It's hard to predict what this flu season will be like, especially with the return to in-person learning in schools and educational institutions," says Dr. Narasimhan. "However, there is one thing we do know: vaccinations for seasonal influenza and COVID-19 prevent sick days, hospitalizations, and deaths due to influenza and COVID-19."

To get our top stories delivered to your inbox, sign up for the Healthy Living newsletter