>>14047277VE against Omicron was 55.2% initially following primary BNT162b2 vaccination, but waned
quickly thereafter. Although estimated with less precision, VE against Omicron after primary
mRNA-1273 vaccination similarly indicated a rapid decline in protection. By comparison, both
vaccines showed higher, longer-lasting protection against Delta. The negative estimates in the final
period arguably suggest different behaviour and/or exposure patterns in the vaccinated and
unvaccinated cohorts causing underestimation of the VE. This was likely the result of Omicron
spreading rapidly initially through single (super-spreading) events causing many infections among
young, vaccinated individuals.
A recent study from England (in preprint) found higher effectiveness against symptomatic Omicron
initially after BNT162b2 vaccination followed by a rapid decline in protection, and that VE increased
to 75.5% (56.1 to 86.3%) two weeks after booster vaccination using unvaccinated individuals as
comparison.
Our study contributes to emerging evidence that BNT162b2 or mRNA-1273 primary vaccine
protection against Omicron decreases quickly over time with booster vaccination offering a
significant increase in protection. In light of the exponential rise in Omicron cases, these findings
highlight the need for massive rollout of vaccinations and booster vaccinations.
