The U.S. government said Wednesday it will start offering booster shots of vaccines against the novel coronavirus in late September, with medical workers and the elderly likely initial targets, amid surging infections led by the highly contagious Delta variant.

The booster shots, aimed at strengthening vaccine efficacy, will be administered eight months after the second dose of the two-dose vaccines developed by Pfizer Inc. and Moderna Inc., pending final approval of the Food and Drug Administration and recommendations from the Centers for Disease Control and Prevention.

Supplied electron micrograph shows the new pneumonia-causing coronavirus. (Photo courtesy of the U.S. National Institute of Allergy and Infectious Diseases)(Kyodo)

"This will boost your immune response, it will increase your protection from COVID-19, and it's the best way to protect ourselves from new variants that could arise," President Joe Biden said at the White House.

"The plan is for every adult to get a booster shot eight months after you got your second shot," he said.

The Biden administration decided to approve booster shots as Israel is already in full swing with administering them, while Germany and Sweden also plan to do so.

On the other hand, the World Health Organization has called for halting the use of coronavirus booster shots until at least the end of September to help ensure access to the vaccines in developing countries, some of which have been unable to secure doses even for medical workers.

But Biden stressed that the U.S. government should not wait to proceed with booster shots until the vaccines are available in most other countries.

"I know there are some world leaders who say America shouldn't get a third shot until other countries got their first shot. I disagree," he said.

"We can take care of America and help the world at the same time," Biden said, noting that his country will continue to work to meet the pledge of donating more than 600 million doses of the vaccines.

A joint statement released by public health and medical experts from the Department of Health and Human Services acknowledged that "many vaccines are associated with a reduction in protection over time" and "additional vaccine doses could be needed to provide long lasting protection."

"We conclude that a booster shot will be needed to maximize vaccine-induced protection and prolong its durability," it said.

Biden also urged Americans who are eligible but remain unvaccinated to receive COVID-19 shots, saying vaccines and masks are the two key tools to protect people from the disease.

In the United States, infection rates have picked up as an easing of restrictions across the country has allowed people to resume their pre-pandemic lifestyles. Florida, Texas and California are among the states hit hardest with new infections, according to the latest tally from Johns Hopkins University.

The cumulative total of U.S. coronavirus infections exceeds 37 million with over 620,000 fatalities, with both figures higher than any other country in the world, the tally showed.

In Japan, the government said Wednesday that half of the country's population has now received at least one dose of COVID-19 vaccine, marking the lowest inoculation rate among the Group of Seven industrialized countries.

Tokyo has not yet decided whether to consider coronavirus booster shots.

On Aug. 12, the FDA approved the booster shots for immunocompromised people who received the Pfizer or Moderna vaccine, while saying others will not need third shots for the time being.