Updated on April 19, 2023.
In the U.S. people ages 65 and older and certain people with weakened immune systems may get an additional dose of the updated versions of ether the Pfizer-BioNTech or Moderna COVID booster. The updated, or bivalent, vaccines made by Pfizer and Moderna carry instructions for fighting both the original strain of the COVID virus as well as Omicron and its descendants.
On April 18, the U.S. Food and Drug Administration updated its emergency use authorization to simplify the vaccination schedule for most people. Regulatory officials say people ages 65 and older can get a second dose of the updated (bivalent) booster at least four months after their last dose. Most people with weakened immune systems who got a bivalent COVID vaccine may receive a second dose at least 2 months later, and receive additional doses as determined by their healthcare provider (HCP).
The FDA says the move is supported by research—including real-world data, involving both the original (monovalent) and updated (bivalent) mRNA COVID vaccines. This data suggests that nearly the entire U.S. population age 5 and older now have antibodies to COVID either through vaccination, infection—or both. But waning immunity over time among older people and those who are immunocompromised may be bolstered by an additional dose.
The FDA’s decision was quickly approved by the Centers for Disease Control and Prevention (CDC), which means people can begin receiving their vaccinations.
All other people who have already received a single booster dose of the updated (bivalent) vaccine are not currently eligible for another dose. The FDA says a decision about additional boosters for the fall will be made this summer.
In the meantime, anyone eligible who hasn’t yet received an updated COVID booster can get one—but the original (monovalent) mRNA COVID vaccines are no longer authorized for use in the United States. The updated Moderna and Pfizer boosters are available for people ages 6 months and older, regardless of whether they previously completed their (monovalent) primary series.
Is the updated booster still needed?
The updated (bivalent) boosters have been available under Emergency Use Authorization since September 2022.
These boosters were reformulated to target the BA.4 and BA.5 omicron subvariants, in addition to the original strain of the virus. BA.4 and BA.5 are no longer in circulation in the U.S. but another Omicron subvariant called XBB.1.5 is responsible for most new infections.
As of April 15, roughly 78 percent of new U.S. COVID cases are caused by XBB.1.5, according to the CDC. Like other versions of Omicron, it has been described as the most transmissible strain to date, more efficient, and more contagious than previous variants.
XBB.1.5 and its close cousins are more likely to successfully evade existing vaccines and treatments. Meanwhile, roughly three years of data shows that COVID immunity—from vaccination, infection, or both—declines over time.
A February 2022 CDC study showed that vaccine effectiveness against COVID-related emergency room visits and hospitalizations was improved by a third dose, but that protection waned over time. After four months, during the first Omicron wave, efficacy against urgent care visits fell from 87 percent to 66 percent and effectiveness against hospitalizations dropped from 91 percent to 78 percent.
Research suggests protection also wanes among those who have recovered from COVID. Another May 2022 CDC study found that vaccine protection against hospitalization among those who are re-infected fell to 68 percent after three doses. Efficacy against hospitalization fell to 35 percent among those who only received two doses of the vaccine.
So, while getting an initial booster improves protection against hospitalization, the original vaccines were designed to protect against the original COVID strain. Ongoing research shows, however, that the updated vaccines trigger a stronger immune response against newer variants than the initial vaccine.
What if you’re still not vaccinated?
In its latest guidance, the FDA says most unvaccinated people may get one dose of an updated bivalent vaccine instead of multiple doses of the original mRNA vaccines.
Children 6 months to 5 years of age who are unvaccinated may receive a two-dose series of the Moderna bivalent vaccine or those ages 6 months to 4 years old can receive a three-dose series of the Pfizer-BioNTech bivalent vaccine. Children who are 5 years of age may receive two doses of the Moderna bivalent vaccine or a single dose of the Pfizer-BioNTech bivalent vaccine.
Children between 6 months and 5 years old who are fully vaccinated are eligible to get an updated (bivalent) booster, but the number of doses will depend on the vaccine and their vaccination history.
