The U.S. Food and Drug Administration approved on Thursday updated COVID-19 vaccines made by Pfizer and Moderna designed to target currently circulating COVID-19 strains and offer better protections against the virus's severe symptoms.

The pharmaceutical companies are set to begin shipping millions of doses of the vaccines in a few days.

A third pharmaceutical company, Novavax, said it expected to have its updated vaccine approved soon.

The Centers for Disease Control and Prevention has recommended the updated shots for people age 6 months and older.

The approval of the new vaccines comes amid a wave of new COVID-19 infections and an increase in COVID-related hospitalizations and deaths in the U.S. However, since the height of the pandemic, demand for the shots has declined.

"We strongly encourage those who are eligible to consider receiving an updated COVID-19 vaccine to provide better protection against currently circulating variants," said FDA vaccine chief Dr. Peter Marks.

"Vaccination continues to be the cornerstone of COVID-19 prevention," he said.

Deciding against the new shot is "a hazardous way to go," said Dr. Robert Hopkins Jr. of the National Foundation for Infectious Diseases. Even if a patient's last infection was mild, without the new vaccine, the next COVID-19 infection could be harsher or even lead to the lingering symptoms of long COVID, he said.

Hopkins also urged people who are at high risk of serious illness or death from the COVID-19 virus to schedule an appointment for the updated vaccine as soon as possible.

High-risk groups include older adults, people with weak immune systems or underlying medical conditions, nursing home residents and pregnant women.

"COVID does not kill many children, thank goodness, but it kills far more children than influenza does," Hopkins said, stressing the importance of the updated vaccines for children and their teachers.

Health officials are also urging people to remember that while earlier COVID-19 infections and vaccinations offer some immunity from the virus, the immunity does not last forever. Last year's shots targeted a strain of the coronavirus that is no longer circulating.

Health officials are also seeking to ease concerns about getting the COVID-19 shot and the flu shot at the same time. Taking the shots together is fine, they said, as well as more convenient.

Some information for this report came from The Associated Press and Reuters.