Immunologists and virologists suggested the four-week interval between initial COVID-19 vaccine doses was likely for trial speed, not immunological necessity, and a longer interval would have been preferable.

“why the four weeks between first and second shot that seems at odds with the little bit that i know about the immune system they said there's not a single reason to do that other than they probably did the trial that way for the sake of speed but they said if you can drag your feet as much as possible between those doses do so”