Biden health officials are recommending Americans take a third dose of the Pfizer-BioNTech and Moderna vaccines eight months after their second shots, in an effort to provide additional protection against the COVID-19 Delta variant.

Pending authorization by the Food and Drug Administration, the booster shots will be offered as soon as the third week of September to nursing home residents, health care workers, and older people who were vaccinated last winter.

People who received the single-dose Johnson & Johnson vaccine will also probably need another dose, officials said. But the results of a clinical trial expected this month will offer more details.

The announcement comes as roughly 40 percent of the U.S. population eligible for the shots are still unvaccinated and as the World Health Organization has called for a moratorium on booster shots until the end of September to make more vaccines available to countries that are behind in vaccinations.