Friday’s announcement by the Food and Drug Administration allowed adults over 18 to be vaccinated. ModernaYou can get your booster shot within five months of the end of their last dose. It will shorten the time period and cut down on waiting by one month.

An FDA authorization was issued earlier in the week to anyone 12 years old who has received the treatment. Pfizer BioNTechGet a booster shot at least 5 months following their last dose.

In October, the Centers for Disease Control and Prevention recommended Moderna boosters for adults. On Wednesday, the CDC reduced eligibility for Pfizer boosters from 12 to 12.

Moderna, Pfizer and others are two of the most frequently administered vaccines in America. Because data has shown that only two doses of boosters are effective against symptoms from the dominant variant in the U.S. omicron virus, but they still provide protection against severe illnesses, there is a shorter waiting period.

A report from the U.K. Health Security Agency last week shows boosters have a 75% success rate in preventing symptoms from omicron after two weeks.

“Vaccination is our best defense from COVID-19 and the circulating variants. Shortening the time between completion of primary series and booster doses may help to reduce waning immunity,” said Dr. Peter Marks of FDA, the FDA responsible for vaccine safety.

Stephane Bancel (CEO Moderna) said yesterday that fourth doses could be needed at some point as boosters are likely to lose their effectiveness over time.

“I will be surprised when we get that data in the coming weeks that it’s holding nicely over time — I would expect that it’s not going to hold great,” Bancel said, referring to the strength of the booster shots.

After four weeks, the U.K. Health Security agency discovered that booster protection decreases. At weeks 5 to 9, boosters were effective in preventing infections by between 5 and 70%, while they are effective for 40% to 50% 10 weeks later.

Pfizer CEO Albert Bourla told CNBC last month that people will likely need a fourth dose, and the shot may be needed sooner than expected due to omicron’s virulence.

According to CNBC’s analysis of Johns Hopkins University data, the U.S. faces an unprecedented Covid epidemic. The average daily number of cases is more than 600,000. This is a 72% increase over the previous week and an unprecedented pandemic record.