Amidst a summer surge of Covid-19 infections, the US Food and Drug Administration just approved updated mRNA vaccines that more closely target the currently circulating variants of the coronavirus.

The updated vaccines, from Moderna and Pfizer/BioNTech, target a variant of Omicron called KP.2, one of the several so-called “FLiRT variants” that collectively are responsible for the current Covid wave. The new vaccines will likely take a few weeks to reach pharmacies and doctors offices.

“Given waning immunity of the population from previous exposure to the virus and from prior vaccination, we strongly encourage those who are eligible to consider receiving an updated Covid-19 vaccine,” said Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, in a statement on Thursday.

The new 2024-2025 formula is meant to boost protection against hospitalization and death due to Covid. In 2023, more than 916,300 people were hospitalized due to Covid-19 and more than 75,500 people died from the virus in the US alone. Vaccination can also protect against long Covid, a chronic condition that lasts at least three months after an infection.

The US Centers for Disease Control and Prevention recommends the new vaccine for everyone 6 months of age and older, whether or not they have ever previously gotten a Covid-19 vaccine.

Like the influenza virus, SARS-CoV-2 is constantly changing. And similar to how flu vaccines are updated every year to adapt to the virus’s changing structure, the Covid vaccines are also being updated. Elizabeth Hudson, regional chief of infectious disease at Kaiser Permanente Southern California says SARS-CoV-2 is changing faster than the flu virus, making it tricky to predict which variants will be dominant by the time the vaccine comes out. “It’s spinning through variants more quickly than what we’re seeing with flu,” she says.

The FDA greenlight comes after an advisory committee in June unanimously recommended that manufacturers develop updated Covid vaccines for this fall. Based on the evidence at the time, FDA advisers initially recommended that the new vaccines target a lineage called JN.1, an Omicron offshoot. But the agency updated its guidance, asking vaccine makers to instead target the KP.2 strain, a descendant of the JN.1 variant, to more closely match circulating variants.

The last version of the Covid vaccine was greenlit by the FDA on September 11, 2023. That formula targeted the XBB.1.5 variant, the predominant one circulating in the US during the first half of 2023. The virus has mutated substantially since then, and the currently circulating FLiRT variants are thought to be more transmissible and evade the immune system more effectively than prior versions of the virus.

If you’ve had a Covid-19 infection recently, the CDC says you can consider delaying your vaccine dose by three months.

“Most of the time, we recommend getting both the Covid and the flu vaccines more towards late September, October, to try to carry people through the winter months,” says Rosha McCoy, a pediatrician and senior director of healthcare affairs at the Association of American Medical Colleges. “Certainly, if somebody is high risk, or is going to be in a high risk situation, they may want to get it sooner.”

Typically, the largest surge of respiratory viruses occurs in the winter. But Covid tends to peak in both winter and summer, and the current summertime surge is likely due to the emergence of new variants and waning protection of the previous vaccine.

“Any natural immunity or vaccine immunity from 2023 has reached a nadir,” Hudson says. “This is sort of a perfect storm for a more infectious form of Covid.”