CONCLUSION
This case-control study confirmed that full or booster vaccination of
three types of vaccines was able to provide limited protection against
Omicron variant infection, although the VE of each type of vaccine
showed slightly different results. There was substantially increased
protection from the booster vaccination (homologous and heterologous
booster vaccinations) against the Omicron variant infection compared
with full vaccination. Moreover, heterologous booster vaccination
conferred better protective immunity against the Omicron variant than
homogenous booster vaccination. The adjusted VEs of the recombinant
protein vaccine were slightly lower than those of other COVID-19
vaccines against the Omicron variant infection. A vaccination campaign
for a booster dose is urgent to be conducted after three doses of
recombinant protein vaccine urgently needs to be conducted and requires
further observation.