Can You Get Two Flu Shots in the Same Season?

With a longer and more severe cold and flu season expected this year, many are wondering if one dose of the influenza vaccine will be enough to ward off severe illness and dangerous respiratory complications. 

With a lot of talk about extra vaccine doses and booster shots for COVID-19, you might wonder if getting two flu shots would offer more protection—or if it’s even possible to get more than one flu shot in the same season.

Just one flu shot a year is recommended (and enough) for most people, but there are exceptions—for example, kids who are getting a flu shot for the first time.

Roshni Mathew, MD, co-medical director of Infection Prevention & Control and pediatric infectious diseases physician at Stanford Medicine Children’s Health, told Verywell that children ages 6 months to 8 years old who “have not previously received a total of two or more doses in their lives need two doses, separated at least by four weeks.”

According to Mathew, “everyone else only needs to get a single influenza vaccine for the season.”

How Well Does One Flu Shot Work?

Each February, the United States works with the World Health Organization (WHO) to determine the formulation of the flu vaccine for the upcoming influenza season. The goal is to closely match the same viruses that are currently circulating and causing illness.

All U.S. flu vaccines protect against type A and B viruses. This includes a flu A(H1) virus, a flu A(H3) virus, a flu B/Yamagata lineage virus, and a flu B/Victoria lineage virus. Flu vaccine components are determined based on current international data, including:

• Which flu viruses are currently making people sick
• How much the viruses are spreading
• The effectiveness of the previous season’s vaccines against the virus
• The ability of the vaccine to provide cross-protection against multiple flu virus types

In some years, flu shots will work pretty well. In others, not so much. A flu vaccine’s effectiveness is affected by a number of factors, including:

• The age and health of the person getting vaccinated
• Which strain of flu virus is going around—e.g., the vaccines tend to offer the most protection against influenza B and influenza A (H1N1) viruses and less against influenza A (H3N2) viruses

Would Two Flu Shots Ever Be Recommended for Adults?

While kids benefit from two flu shots, there is not enough evidence to show that it would be helpful for any other groups to get a second dose.

Some studies in adults with compromised immune systems (like organ transplant recipients) have looked at whether getting a second flu shot might be helpful, but more research is needed before the recommendation would be changed.

Currently, the Centers for Disease Control and Prevention (CDC) states that for adults, “studies have not shown a benefit from getting more than one dose of vaccine during the same influenza season, even among elderly persons with weakened immune systems.”

How Long Does Flu Shot Protection Last?

A flu shot that works well is key to combating a severe flu season, but the length of immunity provided by each annual dose is another key aspect.

According to experts, flu vaccine immunity wanes over time but typically provides protection for five to six months. However, this timeframe depends on different factors like a person’s age and the strain of flu virus that’s going around.

“The length of the influenza season is, indeed, relevant to our strategy for vaccination,” Buddy Creech, MD, MPH, a professor and chair in the Department of Pediatrics at the Vanderbilt University Medical Center and the director of the Vanderbilt Vaccine Research Program, told Verywell. “We know that vaccine effectiveness wanes through the season, with some estimating an approximate 5% loss each month following vaccination.”

That said, Creech added that these numbers are challenging to come by.

“[I] think it’s fair to say that the longer we go after vaccination, the less immunity we have.”

Despite waning immunity over time, the CDC still says that one flu shot is enough to get the general population through an entire flu season. 

“This is part of the reason CDC suggested that older individuals get vaccinated in October rather than being first in line to get them in July or August,” said Creech. “We do not fully know the characteristics of waning immunity in children, but it is clear that vaccinating in the fall protects children through the influenza season, even when it extends into the very late spring.”

Experts suggest people get their annual flu shot in September or at least by the end of October. The flu vaccine is offered as long as the flu virus is circulating in the community, but the U.S. flu season tends to peak in January and then taper down in the spring. 

Which Flu Shot Should You Get?

The CDC recommends that everyone over the age of 6 months get their flu shot. The flu vaccines for the season are available at providers’ offices, pharmacies, and even grocery stores. If you’re over the age of 65, the CDC recommends that you get one of the three high-dose vaccines:

• Fluzone High-Dose Quadrivalent vaccine 
• Flublok Quadrivalent recombinant flu vaccine
• Fluad Quadrivalent adjuvanted flu vaccine

While you most likely only need to get one flu shot per flu season, timing matters. Remember that it takes about two weeks after you get vaccinated for immunity to kick in.