Question:

Do the two vaccine injections have to be perfectly timed apart?

Answered by infectious diseases expert Richard Hankins, MD:

In general, the vaccine timing should match what the clinical trials tested. Pfizer tested three weeks apart and Moderna tested four weeks apart for their two-dose series.

However, the Centers for Disease Control and Prevention advises that "if a delay in vaccination is unavoidable, the second dose of Pfizer-BioNTech and Moderna COVID-19 vaccines may be administered up to six weeks after the first dose."

So if your schedule or the schedule of the vaccine clinic makes it impossible to have the second dose perfectly timed, a delay of a few days is OK.