The Food and Drug Administration on Thursday approved updated Covid vaccines from Pfizer and Moderna, putting the new shots on track to reach most Americans in the coming days amid a summer surge of the virus. 

The jabs target a strain called KP.2, a descendant of the highly contagious omicron subvariant JN.1 that began circulating widely in the U.S. earlier this year. KP.2 was the dominant Covid strain in May, but now only accounts for roughly 3% of all U.S. cases as of Saturday, according to the latest Centers for Disease Control and Prevention data.

Still, Pfizer and Moderna have said their KP.2 vaccines can produce stronger immune responses against other circulating subvariants of JN.1, such as KP.3 and LB.1, than last year’s round of shots targeting the omicron strain XBB.1.5 can.

“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 to provide better protection against currently circulating variants,” Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a statement.

In June, the CDC recommended that everyone over 6 months old receive an updated Covid vaccine and flu jab this year. The new shots from Pfizer and Moderna are specifically approved for people ages 12 and older and are authorized under emergency use for children 6 months through 11 years old.  

Pfizer will begin shipping its new shot immediately and expects it to be available in pharmacies, hospitals and clinics across the U.S. “beginning in the coming days,” the company said in a statement. Moderna also expects its shot to be available in a similar time frame, according to a statement.

“Staying up to date with your COVID-19 vaccine remains one of the best ways for people to be protected and prevent severe illness,” Moderna CEO Stephane Bancel said in a statement. “We appreciate the U.S. FDA’s timely review and encourage individuals to speak to their healthcare providers about receiving their updated COVID-19 vaccine alongside their flu shot this fall.”

The FDA’s approval comes a few weeks ahead of last year’s round of shots, which the agency cleared on Sept. 11.

The earlier arrival of updated vaccines could offer some reassurance to Americans as the nation sees a relatively large spike in the virus this summer. A “high” or “very high” level of Covid is being detected in wastewater in almost every state, according to CDC data. Wastewater monitoring provides a glimpse of how widespread the virus is in the U.S. as other forms of testing have fallen off.

Other measures of the virus are rising but remain far below where they were at the peak of the pandemic. Covid test positivity rates rose to 18.3% for the week ended Aug. 10, from 17.9% the week before, according to the CDC.

Meanwhile, the CDC said about four people are being hospitalized for Covid for every 100,000 people in a given area. That’s up from about one Covid hospitalization for every 100,000 people in May, which was the lowest level since the pandemic began. 

The summer Covid wave may decline by the time the shots reach patients’ arms and kick in an immune response against the virus, which typically takes two weeks after vaccination. 

Still, federal health officials have long told Americans to expect annual updates to Covid shots as the virus churns out new strains that can dodge the immunity people have from previous vaccinations or infections — protection that wanes over time. It’s similar to how the U.S. rolls out new flu vaccines every year. 

It’s unclear how many Americans will actually roll up their sleeves to get another shot in the coming months.

Only around 22.5% of U.S. adults received the latest round of shots that came out last fall, according to CDC data through early May. 

Many Americans who got previous rounds of Covid shots cited a lack of worry about the virus as a reason they didn’t get the latest booster, according to a November survey from health policy research organization KFF. Others said they had been too busy to get their shot, the survey said.

In June, the FDA asked vaccine makers to manufacture shots against JN.1 before telling them to target KP.2 instead “if feasible.”

That shift appeared to put Novavax, which filed for authorization of a new JN.1 shot that same month, at a disadvantage. The FDA has not cleared the biotech company’s jab. 

In a statement, Novavax said it is working “productively” with the FDA as the agency completes its review. Novavax expects its shot to receive authorization in time for peak vaccination season in the U.S.

The company noted that its shot provides protection against descendants of JN.1, including KP.2.3, KP.3, KP.3.1.1 and LB.1.

Novavax manufactures protein-based vaccines, which cannot be quickly updated to target another strain of the virus. Protein-based technology is a decades-old method used in routine vaccinations against hepatitis B and shingles. 

Meanwhile, Pfizer’s and Moderna’s shots use messenger RNA technology, which teaches cells how to make proteins that trigger an immune response against Covid. The mRNA vaccines are much easier to develop and update than protein shots.