The Johnson & Johnson vaccine works differently in the body than the two-dose vaccines, which is why people receive just one dose. This method has been used for many years to develop successful vaccines for use in people.
The one-dose vaccine is a viral vectored vaccine, which uses a harmless type of virus to help the body make a specific protein to trigger an immune response to COVID-19. The two-dose vaccines use messenger RNA, or mRNA, that teach the body how to make a protein to trigger an immune response to COVID-19.
Johnson and Johnson has been granted EUA for a booster dose for select populations. Eligible individuals may choose which vaccine they receive as a booster dose, regardless of which vaccine they received as part of their primary series.