The FDA will likely authorize a secondary booster dose for adults 50 years and older this week.

The booster shot would be for people who were vaccinated with Moderna or Pfizer.

Once approved by the FDA, it will be up to the CDC to follow with a “permissive recommendation," CNN reports.

That means the second booster dose won’t necessarily be recommended, but if people wish to receive it, they can.

With this dose, the FDA will forego its typical meeting with independent vaccine advisors.

There is evidence that shows protection from three shots is waning and that a fourth shot could help boost protection – including data from Israel involving people over the age of 60.

In this study, people had elevated protection from severe disease and hospitalization.

However, critics say there isn’t enough evidence to show the fourth shot is actually needed, or how long protection from it would last.