The Updated COVID Vaccines Are Here: 9 Things to Know

[Originally published: Oct. 2, 2023. Updated: April 19, 2024.]

Note: Information in this article was accurate at the time of original publication. Because information about COVID-19 changes rapidly, we encourage you to visit the websites of the Centers for Disease Control & Prevention (CDC), World Health Organization (WHO), and your state and local government for the latest information.

There has been better protection against severe disease, hospitalization, and death from COVID-19 since newly updated (2023–2024 formula) mRNA COVID vaccines became available last fall. Shots are available to protect everyone 6 months and older from serious illness, hospitalization, and death from the disease.

The Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) approved the updated vaccines by Pfizer-BioNTech and Moderna for everyone 6 months and older, and authorized an updated Novavax vaccine for those 12 and older in the fall of 2023. In February of this year, the CDC recommended an additional dose for adults ages 65 and older.

The vaccines target XBB.1.5, a subvariant of Omicron that dominated the United States—and the world—from November 2021 until last year. The CDC says the updated vaccines should also work against currently circulating variants of the SARS-CoV-2 virus—many of which descended from, or are related to, the XBB strain. The vaccine is also expected to protect against JN.1, the current dominant strain in the U.S.

While COVID has been causing mostly mild illness recently, Yale Medicine infectious diseases specialist Onyema Ogbuagu, MBBCh, reminds people that the disease can still lead to hospitalization and death. “Infections can have long-term consequences,” Dr. Ogbuagu says, adding that even healthy people can develop Long COVID—a condition in which new, continuing, or recurring (and sometimes debilitating) symptoms are present four or more weeks after an initial coronavirus infection.

Below, Yale experts tell you what you need to know about the updated COVID vaccine.

The updated vaccines are not expected to prevent all cases of COVID, including those causing mild illness; rather, their aim is to reduce severe illness, hospitalization, and death from infection. According to the CDC, COVID is still a major cause of serious respiratory illness. While hospitalizations and deaths from COVID have been declining, 7,318 people were hospitalized with the disease during the first week of April 2024 alone (that number rose as high as 35,000 during one week in January, a month when respiratory diseases tend to peak).

Older people (especially those ages 50 and older) are more likely than younger people to get very sick from COVID. Immunocompromised people and those with chronic medical conditions, such as diabetes or heart disease, are at the highest risk of severe disease and death, but some young, healthy people have also gotten very ill and died from COVID. In addition, the CDC recommends the vaccine for pregnant women to protect both mother and baby.

An analysis by the CDC in September 2023 suggested that making its vaccine recommendation universal could prevent 400,000 hospitalizations and 40,000 deaths in the U.S. over the next two years.

The bivalent booster, which is no longer available, was introduced in the fall of 2022. It targeted the BA.4 and BA.5 Omicron subvariants and the original SARS-CoV-2 virus. The updated vaccine is monovalent, designed to prevent severe disease from the Omicron XBB.1.5 subvariant. By September 2023, the long-running XBB.1.5 accounted for only about 3% of cases in the U.S., but most of the strains circulating now are descended from (or closely related to) it.

That’s a good example of how the virus has evolved—and it’s still evolving—so rapidly that it may be impossible to match each new vaccine update to the variants circulating at the time it is released, explains Scott Roberts, MD, a Yale Medicine infectious diseases specialist. “But we know from experience that the vaccines hold up very well, even against multiple variants, unless there is a significant shift like we saw with Delta to Omicron in the winter of 2021,” he says. “Basically, if you have some immunity to a variant and are exposed to a new offshoot of it, you’ll have some protection.”

The FDA is calling the newest shots “updated vaccines” in anticipation of needing to provide updated formulas annually, similar to the flu shot, which changes each year.

A booster shot gives a “boost” to the recipient's existing immunity from a previous vaccination. Updated vaccines are different in that they are expected to provide protection against currently circulating variants, helping the body build a new response to those variants. “Barring the emergence of a markedly more virulent variant, the FDA anticipates that the composition of COVID vaccines may need to be updated annually, as is done for the seasonal influenza vaccine,” the FDA noted in its approval and authorization of the new vaccine.

“I think we're going to fall into a pattern very similar to the flu, where every year the virus is going to mutate slightly, and the vaccine formulation for the fall will be an educated guess,” says Dr. Roberts. “We will make a vaccine targeted against whatever we predict or whatever is currently circulating and hope our vaccines are a good match, because we will be developing them before we know what variants will be circulating in the fall."

COVID vaccines are safe and effective, according to the CDC. The safety of COVID vaccines has been rigorously monitored and evaluated since their emergency use authorization (EUA) in December 2020. According to the CDC, the updated mRNA COVID vaccines for 2023-2024 are manufactured using a similar process to the previous vaccines.

The benefits of the COVID vaccine continue to outweigh any potential risks, and serious reactions after COVID vaccination are rare, according to the CDC. The agency cited a study showing the risk of cardiac complications, including myocarditis (an inflammation of the heart muscle) was significantly higher after a COVID infection for both males and females in all age groups.

The FDA approved the updated mRNA vaccines for adolescents and teenagers ages 12 and older and authorized them for emergency use in children ages 6 months through 11 years.

Children are less likely to get seriously ill with COVID, but some still do, says Magna Dias, MD, a Yale Medicine pediatric hospitalist. She tells parents who are still not sure whether they should get the vaccine for their children to talk to their pediatrician, especially if their child is immunocompromised. “In that case, I think it’s a no-brainer to protect them,” she says.

The FDA authorized an updated version of a vaccine Novavax developed to target the XBB.1.5 strain. Individuals 12 and older previously vaccinated with a COVID vaccine (and who have not already been vaccinated with a recently updated mRNA COVID vaccine) are eligible to receive one dose; unvaccinated individuals can receive two doses.

According to the FDA, the updated vaccine addresses currently circulating variants to provide better protection against serious consequences of COVID, including hospitalization and death.

The Pfizer-BioNTech and Moderna vaccines use messenger RNA (mRNA) technology, which instructs the body’s cells to make proteins that trigger an immune response against COVID. The Novavax protein-based vaccine uses an older, more traditional technology and a different mechanism—it directly injects the spike protein (formulated in a laboratory) and another ingredient into the body, leading to the production of virus-fighting antibodies and T cells. The Novavax vaccine is the only non-mRNA COVID vaccine available in the U.S.

People 5 years and older may get one dose of the updated vaccine at least two months after the last dose of any previous COVID vaccine. Babies and young children usually need more doses than older children and teens. Anyone who recently had COVID may consider delaying their vaccine by 3 months.

People who are 65 or older should receive their second dose of the updated vaccine at least four months after the first dose. Those in that age group who are immunocompromised should get the additional dose earlier—at least 2 months after the first one.

The CDC considers it safe to get the COVID shot and annual flu vaccine simultaneously. There is even research in progress to explore the effects of administering both vaccines in a single shot.

But the respiratory syncytial virus (RSV) vaccines for older adults and pregnant women (who can pass the antibodies along to their newborns) were brand new in fall 2023, and there isn’t data to say for sure whether giving those at the same time as the other two shots is the best strategy.

As with previous COVID vaccines, this one will be available at participating pharmacies and provider offices. To find a location near you that carries the vaccine and to schedule an appointment, go to Vaccines.gov. You can also call 1-800-232-0233 (TTY 1-888-720-7489). Be aware that current distribution and insurance issues may delay availability of the vaccines temporarily in some places.

According to the CDC, the vaccines are covered by insurance, including private insurance, Medicare plans, and Medicaid plans. Uninsured children and uninsured adults also have access through the Vaccine for Children Program and Bridge Access Program, respectively.

Information provided in Yale Medicine articles is for general informational purposes only. No content in the articles should ever be used as a substitute for medical advice from your doctor or other qualified clinician. Always seek the individual advice of your health care provider with any questions you have regarding a medical condition.