WASHINGTON — The U.S. Food and Drug Administration on Thursday approved an updated COVID-19 vaccine intended to address severe symptoms of the virus ahead of the cold and flu season.

The new booster shots from Moderna and Pfizer follow a summer of increasing COVID-19 cases and are designed to better address the variants that are circulating now.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a written statement that vaccination “continues to be the cornerstone of COVID-19 prevention.”

“These updated vaccines meet the agency’s rigorous, scientific standards for safety, effectiveness, and manufacturing quality,” Marks said. “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.”

Wastewater surveillance has been steadily increasing since early May and could rise further now that children throughout the country are returning to school.

The number of emergency department visits began increasing in May as well. And while the death rate from COVID-19 steadily decreased during the first half of the year, it began ticking up slightly in June, according to data from the Centers for Disease Control and Prevention.

The FDA announcement said that three doses of the updated Pfizer-BioNTech vaccine or two doses of the updated Moderna vaccine are approved for unvaccinated children between six months and 4 years old.

Children between six months and 4 years old who have already received their COVID-19 vaccine are eligible to receive one or two doses or either updated vaccine. The dosing will depend on the timing and number of doses of their previous vaccination.

Children between 5 and 11 years old can receive a single dose of the updated vaccine, regardless of whether they’ve been previously vaccinated or not. If a child in that age range has been vaccinated against COVID-19, they need to wait at least two months before getting the updated dose.

Anyone over the age of 12 is eligible for a single dose of the updated vaccine if they’ve been vaccinated previously. They also must wait at least two months after their last vaccination.

Pfizer wrote in a statement that its “vaccine will begin shipping immediately and be available in pharmacies, hospitals, and clinics across the U.S. beginning in the coming days.”

Moderna said it expects its updated vaccine “to be in pharmacies and care settings in the coming days.”