I am due to be vaccinated against Covid today. Let us suppose that I receive either the Pfizer/BioNTech (BNT162b2) or Moderna (mRNA-1273) vaccine, and subsequently receive my second dose on schedule (21 days later for BNT162b2; 28 days later for mRNA-1273).
Data from phase III trials for these vaccines suggest substantial efficacy at preventing disease starting at 14 days after the first dose:
While confidence intervals are wider due to the relatively small number of observation days, the BNT162b2 vaccine appears to be 92.6% effective in the corresponding 14- to 20-day window, while the mRNA-1273 vaccine appears to be 94.2% effective in the corresponding 14- to 27-day window. This is comparable to their efficacies even ≥14 days after the second dose.
Data for severe disease is also promising, though much sparser and hence more difficult to interpret.
On the other hand, at least one large observational study estimates only 57% efficacy against symptomatic Covid-19 for BNT162b2 in the 14- to 20-day window, as compared to 94% ≥7 days after the second dose. Other measures (documented infection, hospitalization, and severe disease) are similarly worse during that window.
In my case, I’m planning on air travel within the continental United States relatively soon, and while I could postpone it several additional weeks if necessary to protect myself and other travelers from severe disease, I prefer not to if there’s no advantage. So, which studies provide the most important evidence about the relative risk of “returning to society” 14 days after my first dose, as opposed to waiting until 7 or even 14 days after my second dose?