Background The spread of the vaccine-resistant Omicron severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2) variants threatens unvaccinated and fully vaccinated
individuals, and accelerated booster vaccination campaigns are underway to mitigate the
ongoing wave of Omicron cases. The immunity provided by standard vaccine regimens,
boosted regimens, and immune responses elicited by vaccination plus natural infection
remain incompletely understood. The magnitude, quality, and durability of serological …