On Wednesday, Oct. 21, the FDA approved booster doses of COVID-19 vaccines manufactured by Moderna and Johnson & Johnson. It also authorized the "mix and match" of any of the three vaccines for the booster doses. 

On Thursday, Oct. 22, the CDC endorsed the Moderna and Johnson & Johnson booster decision, giving the green light to begin implementation by the end of the week.

FDA Commissioner Janet Woodcock said in a statement that "science has shown that vaccination remains the safest and most effective way to prevent COVID-19, including the most severe consequences of the disease." 

How can vaccines be mixed?

Depending on which type of vaccine has been given, various combinations are possible. 

If, for example, a person has the J&J single-dose vaccine, he or she could opt for a Moderna (half-dose) or Pfizer booster.

On the other hand, those who have the two doses of Pfizer or Moderna could choose from any of the three available (Moderna, Pfizer, or J&J) for the booster. The FDA also clarified that if the patient has the full Pfizer vaccination, a half dose of Moderna could be applied. 

"The use of a single booster dose of the Janssen (Johnson & Johnson) vaccine can be administered at least two months after completion of the primary single-dose regimen," the FDA explained in a statement.

As for the Pfizer-BioNTech and Moderna vaccines, the recommendation is six months after completion of the initial regimen. 

According to the CDC and the FDA, the booster dose is recommended primarily for people at higher risk of infection and/or complications from COVID-19. 

The Pfizer-BioNTech and Moderna booster is recommended for patients over 65 years, as well as for those over 18 years of age who are at risk of comorbidity or are exposed to the virus in the workplace. 

For the Johnson & Johnson booster, the recommendation is to apply it to all persons over 18 years of age.