When's the best time to get your flu shot?

The weather is getting colder, school is back in session, and seasonal respiratory viruses are already starting to ramp up for fall. Although influenza season has not started yet in the United States, experts are already spreading the word about the best time to get the flu shot.

The flu is a common and highly contagious respiratory illness caused by influenza viruses. In the U.S., flu season typically occurs during the fall and winter months when influenza viruses, which can spread year-round, circulate at much higher levels.

“Right now, in the latter part of September, we’re seeing occasional cases of flu here and there ... which is what we would anticipate in a normal, pre-pandemic season,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, tells TODAY.com.

According to the U.S. Centers for Disease Control and Prevention’s “FluView” weekly surveillance report for the 2023-24 season published on Sept. 9, less than a few hundred cases have been reported to the CDC so far. However, cases are expected to increase.

The timing and duration of flu season varies from year to year, but flu activity typically starts to ramp up in October then peaks between December and February. Significant activity can continue as late as May, according to the CDC.

In light of last winter, experts are urging Americans to be cautious. "Last year, flu season started early and very vigorously," says Schaffner. After a pandemic lull, influenza activity surged and flu-related hospitalizations reached record highs during the 2022-23 season, TODAY.com previously reported.

The tough flu season coincided with a surge in respiratory syncytial virus, or RSV, among infants and young children and a simultaneous wave of COVID-19 last fall — creating a “tripledemic" of respiratory viruses that lasted well into winter around the country.

What do we know about the 2023-2024 flu season so far, when is the best time to get a flu shot this year, and how else can you and your family prepare for this winter? We spoke to experts to answer all of your flu season questions.

When is the best time to get a flu shot?

“The optimal time is right at the end of September and through the month of October (for most people),” says Schaffner. Getting the flu shot at this time allows protection to build before the flu activity ramps up, and that protection will extend through the winter.

The flu shot does not work right away because it takes time for the body to develop antibodies, which help fight off the virus. “It takes seven days to 10 days usually, and in some people up to two weeks after you get your inoculation (to be protected),” says Schaffner.

People should aim to get it before the end of October and before flu activity ramps up. “You don’t want to get vaccinated during the flu season. ... The biggest benefit is when you get vaccinated before the season starts,” Dr. Albert Ko, an infectious disease physician and professor of public health, epidemiology and medicine at Yale School of Public Health, tells TODAY.

Some children may need two doses of the flu vaccine, which are given at least four weeks apart, per the CDC. For those children, the it is recommended to get the first dose as soon as possible.

What can we expect for the 2023-24 flu season?

"So far, we appear to be on a track for a more normal season,” says Schaffner, adding that cases are expected to accelerate in November and, by the beginning of the year, become widespread throughout the country. “With the flu, things can change in a week, but right now we’re just seeing scattered cases,” Schaffner says.

It's difficult to predict how the rest of flu season will unfold at this point, but researchers often look to the Southern hemisphere for clues. In temperate regions of the Southern hemisphere, flu activity peaks earlier in the calendar year, and flu season falls between April and September, per the CDC.

“It’s not a direct predictor of what happens here in the U.S.,” says Ko. However, it can offer some insight into what kind of flu season the Northern hemisphere may experience.

Scientists keep a close eye on Australia as a possible harbinger of flu trends in the U.S., NBC News previously reported. "The Australians had a moderately severe influenza season this year," says Schaffner.

Last year, the tough flu season was attributed to several possible factors, according to experts. Reduced exposure to influenza viruses during the pandemic may have caused immunity to wane, creating a more vulnerable population.

Dropping of COVID-19 mitigation measures, which had previously helped to suppress the flu and other respiratory viruses, allowed ample opportunity for influenza to spread.

"I do expect that we'll be returning to (typical) seasonal flu patterns (this year),” Ko says. However, the severity of flu season in the U.S. has always varied from year to year, even before the pandemic, Ko notes, so it's important for people to be prepared.

How to protect yourself during flu season

Fortunately, there's a safe way to build up immunity and protect yourself ahead of flu season: the seasonal flu vaccine, which the CDC recommends for everyone ages 6 months and older.

The flu shot is widely available, free under most health insurance plans and safe. According to the CDC, getting a yearly flu shot is recommended as the “first and most important step in protecting against flu viruses," and it also reduces the burden of flu illness, hospitalizations and deaths.

Influenza sickens millions of people and causes anywhere from 10,000 to 52,000 deaths in the U.S. every year during flu season, Dr. Andy Pekosz, virologist at the Johns Hopkins Bloomberg School of Public Health, previously told TODAY. “It’s not something that is insignificant in terms of how much danger it poses to the population,” he added.

Even if you've never gotten a flu shot before, it's not too late to start. "Influenza is a nasty virus, particularly for older frail people and people with underlying illnesses ... but the more we all get vaccinated, the better we protect ourselves and others," says Schaffner.

How long does the flu shot last?

How long protection from the flu shot lasts varies by person and timing of the flu shot, but generally if you get the vaccine in October, protection should last through the winter and into March, says Schaffner.

"Younger, healthier people who have a more robust immune systems may get protection well beyond the winter," says Schaffner.

All of the flu shots for the 2023-2024 season are quadrivalent, meaning they protect against four different flu viruses, per the CDC. “There are always two influenza A strains and two influenza B strains. ... We include four different strains because more than one strain is usually active at any one time,” says Schaffner.

Occasionally the season starts with A strains being more active and ends with B strains being more active, Schaffner adds, which is why the shot can offer continued protection for months.

Is it better to get the flu shot earlier or later in the season?

It's better to get the flu shot earlier in the season; the public health guideline is to get it before the end of October. But as long as you're getting it within the recommended timeframe of late September to late October, it doesn't really matter if you get it earlier or later, unless you have an underlying health condition. (And while you'll get more protection getting the flu shot earlier, there's no such thing as "too late" to get the flu shot.)

"(For) people who are older or have underlying chronic illnesses, the timing of the vaccine is more important because their immune systems don’t respond optimally," says Schaffner. "We ask them to wait until October to get the vaccine because we want the protection to extend through the entire winter season into March."

In any case, aim to get your flu shot before the end of October and flu activity ramps up. “The bottom line is that you don’t want to wait until you’re already going to be at risk of getting influenza to get vaccinated,” Ko said. "It's a preventive vaccine."

When is it too late to get a flu shot?

Although earlier is better, it is never "too late" to get the flu shot, the experts emphasize. “If you’ve never had the flu shot, no matter where you are during the season, you should get it … but the greatest protection, of course, (comes from) when you get it before the season starts,” said Ko.

The flu shot can still provide protection if you get it later in the season when flu activity peaks, according to the CDC.

So try to get the shot before November if you can, but better late than never. “The timing of the flu shot is kind of like timing the stock market. You really don’t want to think too much about it — you just sort of have to get it when you can,” said Pekosz.

It’s hard to predict exactly when this flu season will end, but based on the trends prior to COVID, flu season will likely end around April or May.

Which flu vaccines are available?

There are several different types of flu shots available — the one that is appropriate for you will depend on your age, health status, allergies and other factors. “It’s always good to talk to a primary health care provider who knows you well,” said Ko.

According to the CDC, these are the flu vaccines available for the 2023-24 season:

Standard dose flu shot: These vaccines are manufactured using inactivated (killed) influenza virus grown in eggs and recommended for everyone aged 6 months to 64 years (including pregnant women), per the CDC.

Nasal spray vaccine: This nasal mist uses live, attenuated (weakened) virus, and it's approved for people from 2 to 49 years of age, Ko said, but it is not recommended for pregnant or immunocompromised individuals.

High-dose flu shot: This egg-based flu shot contains four times the antigen of the standard-dose, inactivated virus vaccines to produce a stronger immune response in the body. It’s approved for individuals 65 and older, per the CDC.

Adjuvanted flu shot: This is an egg-based flu shot approved for people 65 and older that contains an adjuvant, which makes an individual have a stronger immune response, per the CDC.

Cell-based flu shot: This flu shot contains virus that was grown in cell culture, so it is completely egg-free, and it’s approved for people 6 months and older, per the CDC.

Recombinant flu shot: This is an egg-free flu shot made using recombinant technology, which contains three times the antigens of standard-dose flu shots, per the CDC, and it is approved for adults aged 18 and older.

Flu shot side effects

Side effects from the flu vaccine are generally mild and, according to the CDC, may include:

  • Redness or soreness at the injection site

  • Mild headache

  • Fever

  • Fatigue

  • Muscle aches

Another important note: You can’t get the flu from the flu shot, Pekosz said. If you have questions, always talk to your doctor.

How effective is the flu shot?

The efficacy of seasonal flu vaccines varies from year to year, but recent studies show that it can reduce the risk of flu illness by 40%. to 60% when most of the virus strains in the vaccine match the strains circulating that season, according to the CDC.

The strains in this year's shot are well-matched to those circulating in the Southern hemisphere, Schaffner notes, but it's hard to know exactly how well the shots work until after the season ends and there's more data available.

There is historical evidence that the flu shot reduces the severity of illness if you do get infected after vaccination and prevents flu-related complications in individuals with chronic health conditions, according to the CDC. So just because it doesn't always prevent infection does not mean it's not working, the experts emphasize.

"By getting flu vaccine, you take a more serious infection and you turn it into a milder one. ... The vaccines keep us out of the emergency room, prevent hospitalizations, ICU admissions and death," says Schaffner.

A secondary effect of the vaccine is that it helps reduce the burden of influenza on health care systems during fall and winter, Ko adds.

We don’t have data on the efficacy of the flu vaccine for this upcoming 2023-2024 flu season yet, but this will become available towards the end or after the season.

Can I get my flu shot and COVID-19 booster at the same time?

Amid an uptick in COVID-19 infections and hospitalizations in the U.S., officials are encouraging Americans to get the new COVID-19 booster this fall. The CDC recommends everyone ages 6 months and older get the updated vaccine, which has been reformulated to target new variants, TODAY.com previously reported.

You can get a flu shot and the new COVID-19 booster at the same time during the same appointment — but you may want to get them in different arms, says Schaffner.

“There isn’t any scientific evidence that tells you that you have to space them out,” said Ko.

“I encourage people to get both at the same time ... especially if you’re in one of the high-risk groups for COVID-19 or influenza ... whether it be the elderly, the immunocompromised, people with secondary medical conditions,” says Pekosz.

In addition to the COVID-19 booster, a new RSV vaccine is also available for pregnant individuals (to prevent RSV in newborns), and individuals ages 60 and older.

All three of these vaccines — for flu, COVID and RSV — can help prevent serious disease and complications, says Schaffner.

How to prepare for flu season

In addition to getting vaccinated, you can also prevent the spread of flu and other respiratory viruses by taking simple preventive steps.

These include avoiding contact with sick people, covering coughs and sneezes, washing your hands and disinfecting contaminated surfaces. Influenza viruses are highly contagious and spread from person to person through respiratory droplets, per the CDC.

If you do get sick with the flu, it's important to monitor symptoms. Flu can range from mild to severe, but most people will recover without needing medical care or treatment, the experts note

Flu symptoms

The most common flu symptoms include:

  • Fever

  • Body aches

  • Headache

  • Fatigue

  • Chills

  • Cough

  • Sore throat

  • Stuffy nose

The CDC recommends staying home for at least 24 hours after your fever is gone (except to seek medical attention) and to contact your health care provider if you are concerned, feeling very sick, or in a high-risk group (over 65, immunocompromised, pregnant, etc.).

There are also flu antivirals available, such as Tamiflu, but these require a prescription from a doctor. "Those work really well in terms of keeping people out of the hospital and limiting disease severity," says Pekosz, adding that these are particularly important for high-risk groups.

Ultimately, the goal is to prevent people from getting sick in the first place. “When we’re thinking about public health, the most efficient thing is to prevent disease rather than wait until people are sick and they need to get treated,” Ko notes.

“These vaccines are available now and people should get them starting now so their immune systems can be best prepared,” says Ko.

This article was originally published on TODAY.com