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COVID-19 Vaccine Boosters

What You Need to Know

COVID-19 vaccines are remarkably effective, even against the omicron variant, but their protection can wane over time. That can lead to breakthrough infections in vaccinated people. A booster — an extra dose, taken several months after your last shot — can fortify your immune response to the vaccine.

Currently, everyone 5 years of age and older is eligible for a booster. The Centers for Disease Control and Prevention recommends a Pfizer-BioNTech booster dose for children of ages 5-17 at least five months after receiving their first two doses of vaccine. Adults 18 and up may receive the Pfizer or Moderna booster. A second Pfizer or Moderna booster is recommended for everyone over 50. Evidence suggests boosters will be a good way to maintain peak protection, particularly for those who are older, have chronic health conditions, or are at higher risk due to their occupation or where they live.

Learn more about what boosters are, how they work, and why they’re being recommended.

UPDATED: 5/20/2022

Boosters are common for many vaccines

Vaccines train our immune systems to prevent disease. They raise infection-fighting proteins, called antibodies, to levels that block viruses or bacteria. Often, more than one dose is needed to bring antibody levels high enough to do the job. Doctors refer to these multiple shots as a series, given on a schedule over months or years. A booster is just an added dose, beyond the first series.

Many vaccines require a multi-dose series and a refresher sooner or later. For example, childhood vaccines against tetanus and whooping cough come in a scheduled series of five shots; measles requires two; hepatitis B, three. To refresh their defenses, adults get a tetanus booster every 10 years. Boosters are a customary, smart way to help our immune system stay ready.

Some vaccines need boosters more often

Booster A
A. INITIAL SERIES: The first vaccine series triggers naïve B cells to turn into antibody-making B cells (blue) and memory B cells (pink), which stand ready to respond to later exposures. Over time, antibodies and antibody-making cells wane.
Booster B
B. BOOSTER: Memory B cells respond quickly to a vaccine booster dose, producing more antibody-making cells that replenish the protective antibodies.

There are two reasons to refresh your immune system with a booster. First, the number of antibody-making factories, called B cells, declines over time. After their first exposure to either a vaccine or an actual infection, some virus-specific B cells turn into long-lived “memory” B cells that remember the threat, ready to spring into action if you’re exposed again. Boosters replenish your well of antibody-making B cells by prompting more B cells — mostly memory B cells — to make antibodies. The sooner your antibody factories dwindle — which can take months, years or decades — the sooner you need a booster.

Second, viruses can also evolve variants that sidestep the antibodies stimulated by the original vaccine. Flu is caused by a virus that changes its surface proteins to avoid detection by our immune system, and flu vaccine antibodies fade in six months. So, we have to fine-tune our defenses with a new flu shot annually. We may need to do the same against SARS-CoV-2, the virus that causes COVID-19, to keep up with new variants. Although doctors don’t yet know whether COVID-19 would, like flu, require annual shots, we do know that so far vaccines remain a strong defense against hospitalization and other major complications from the COVID-19 variants.

Will boosters protect against omicron and delta?

Very likely. Evidence is mounting that both the initial vaccine series and a booster, when recommended, will protect against serious illness from the omicron variant, which is more prone than earlier variants to cause breakthrough infections. White House chief medical adviser Dr. Anthony Fauci says that boosters raise protection against symptomatic disease from omicron to 75%. The CDC recommends that all those 5 years and older get a booster as soon as they qualify, based on the required interval after their initial shots. Only the Pfizer booster is authorized for those ages 5-17.

Omicron, which emerged in late November 2021, quickly replaced delta as the predominant COVID-19 variant in the U.S. The delta variant, which arose in December 2020, was more than twice as contagious as the original coronavirus that emerged in Wuhan, China. Omicron is thought to be three times more contagious than delta. While all three vaccines authorized in the U.S. were designed to stop the original strain, they are all still effective against delta, which may continue to circulate despite the strength of omicron. 

Immunocompromised people really need boosters, ASAP

Individuals with compromised immune systems, about 2.7% of the U.S. population, are especially vulnerable to severe COVID-19 infections. They include cancer patients, transplant recipients, people with untreated HIV and those treated with drugs that suppress the immune system. Tests have shown that the two-dose Moderna and Pfizer vaccine regimens do not provide as much protection among this population. The CDC has since recommended a three-dose series for those in this group with the third dose at least 28 days after the second, to be followed by a booster five months later, for a total of four shots. For children aged 5-17, only the Pfizer boosters are approved. For immunocompromised people who took the Johnson & Johnson vaccine, the CDC recommends a Moderna or Pfizer booster two months after the first shot. To protect those with weakened immune systems, it’s important that they receive boosters and for those in close contact with them to be vaccinated.

Are boosters just as safe as the first doses of vaccine?

Yes. No new safety concerns have been raised for boosters. Some people can expect to experience the same discomfort that can occur after the first or second shot, such as a sore arm, fatigue, mild fever or headache. Extremely rare, more serious reactions have occurred in the initial series. The two mRNA vaccines, Pfizer and Moderna, have been associated with very rare (and usually mild) cases of heart inflammation, mostly in males 18-30 years old. The single-shot Johnson & Johnson’s vaccine is associated with an extremely rare risk of blood clotting, which can be very serious, among women aged 18-49. As a result, the CDC has declared since Dec. 23, 2021, that the mRNA vaccines are “preferred” over the J&J shots, and on May 5, 2022, the FDA further restricted access, making it available only to adults who cannot access mRNA vaccines or cannot take them for medical reasons, such as allergic reactions.

When should I get my booster?

The right timing for a booster shot differs from person to person. The CDC says that all those ages 18 and older who received a single-dose J&J vaccine should get a booster at least two months after receiving their first shot, but since Dec. 23, 2021, prefers it be a Pfizer or Moderna mRNA-based vaccine. Those who received two doses of the Moderna or Pfizer vaccine the first time around can get an mRNA booster, at least five months after their second dose. With the emergence of the omicron variant in November 2021, the CDC stresses everyone over the age of 18 “should” get a booster as soon as they are eligible based on time after their first series. On May 19, 2022, the FDA extended authorization for a Pfizer booster for childen young as 5, to be administered five months after their initial series.

For the best advice, review up-to-date COVID-19 booster information from the CDC and stay in touch with your doctor. If something nudges up your risk of COVID-19, whether it is your age, a pregnancy, the health of your immune system, an underlying health problem or a high-risk exposure, your health care provider may suggest you schedule your booster sooner rather than later.

If I’ve gotten one manufacturer’s vaccine, can I be boosted by another’s?

Yes. In October 2021 the CDC agreed it was acceptable to “mix and match,” taking a booster using a different vaccine brand than your first shots. However, because of concerns over rare but potentially serious side effects associated with the J&J vaccine, the CDC in December 2021 said that it is preferable in most situations to be boosted, when appropriate, with either the Moderna or Pfizer vaccines.


Will boosters end the pandemic?

They’ll help, but they’re still not the most important factor. Boosters can reduce the spread of COVID-19 in highly vaccinated countries and, if proven effective against new variants like omicron, provide people with more confidence they are fully protected. Most research suggests that the quickest way to reduce deaths and end the pandemic is to get as much of the world vaccinated with the initial series as soon as possible. Providing vaccine protection to the unvaccinated will have more of an impact on the continued spread of COVID-19 than maintaining the highest levels of protection among those who have had their first shots. Track current global vaccination rates at the New York Times COVID-19 dashboard.

Will we need boosters every year?

We don’t know yet. Many researchers expect COVID-19 to become a fixture of our lives, much like the seasonal flu. The virus has surprised scientists with how quickly it’s mutated into new variants like delta and omicron. Although COVID-19 is changing rapidly, similar to influenza — a respiratory virus that requires seasonal vaccines — no one knows yet how COVID-19 vaccines will stand up over time. All of the COVID-19 boosters currently available are based on the original virus from late 2019, so our vaccines may need to adapt as the virus changes. Scientists are designing future boosters that target variants and organizing studies to better understand long term immunity.

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