ST. LOUIS (KTVI) — There has been some confusion over COVID-19 booster shots, so here’s what medical officials are saying the situation is right now. 

Health care systems are already giving out COVID booster shots to the elderly and immunocompromised individuals who are at the highest risk if their immunity wanes.

The Centers for Disease Control and Prevention is considering recommending the first boosters go to front-line health workers who can’t come to work if they get even a mild infection. The Food and Drug Administration is set to meet on Sept. 17 to discuss COVID-19 booster shots, and a federal government announcement will be made soon after that meeting.  

If the FDA approves another dose, then advisers to the CDC will recommend who should get one.

“We do know that boosters do boost the immune system. They increase anti-body levels, and in population-based studies, they appear to decrease the risk of infection,” said Dr. Clay Dunagan, with the St. Louis Metropolitan Pandemic Task Force. 

Vaccines train the immune system to fight the coronavirus, including by producing antibodies that block the virus from getting inside cells. People harbor huge levels right after the shots. But just like with vaccines against other diseases, antibodies gradually drop until reaching a low maintenance level.

A booster dose revs those levels back up again.

The timing for giving a booster matters because the immune system gradually builds layers of protection over months. Give a booster too soon, before the immune response matures, and people can miss out on the optimal benefit, said Dr. Cameron Wolfe, an infectious disease specialist at Duke University.

However, Clay said the “optimal timing” is still unclear.

“There’s been talk about giving it after eight months; some have said after six months; some have said after a year,” he said. “Those are really issues that are being worked out looking at a variety of sources of information from countries that have started to use boosters as well as additional studies that the pharmaceutical companies have done.”

Nevertheless, Dunagan says he believes COVID booster shots will be available by the end of the year. 

The initial plan was to offer Pfizer or Moderna boosters starting Sept. 20, contingent on authorization from U.S. regulators. But now administration officials acknowledge Moderna boosters probably won’t be ready by then — the FDA needs more evidence to judge them. Additionally, Moderna wants its booster to be half the dose of the original shots.

As for Pfizer’s booster, it isn’t a simple decision on who really needs another dose right away. What’s ultimately recommended for an 80-year-old vaccinated back in December may be different than for a 35-year-old immunized in the spring — who likely would get a stronger immunity boost by waiting longer for another shot.

Currently, there are about 150,000 new COVID-19 cases daily, and the delta variant is filling hospitals, children are getting sick, and some schools are abruptly switching back to remote learning because of outbreaks. The U.S. death toll stands at more than 650,000, with one major forecast model projecting it will top 750,000 by Dec. 1.

The Associated Press contributed to this report.