High rate of BA.1, BA.1.1 and BA.2 in triple vaccinated

BackgroundBooster vaccine doses offer protection against severe COVID-19 caused by omicron but are less effective against infection. Characteristics such as serological correlates of protection, viral abundance, and clearance of omicron infection in triple vaccinated individuals are scarce. MethodsWe conducted a 4-week twice-weekly SARS-CoV-2 qPCR screening shortly after an mRNA vaccine booster in 368 healthcare workers. Spike-specific IgG levels and neutralization titers were determined at study start. qPCR-positive participants were sampled repeatedly for two weeks and monitored for symptoms. ResultIn total 81 (cumulative incidence 22%) omicron infections were detected, divided between BA.1, BA.1.1 and BA.2. Increasing post-booster antibody titers were protective against infection (p<0.05), linked to reduced viral load (p<0.01) and time to viral clearance (p<0.05). Only 10% of infected participants remained asymptomatic through the course of their infection. Viral load peaked at day 3 and live virus could be detected for up to 9 days after first PCR-positive sample. Presence of symptoms correlated to elevated viral load (p<0.0001), but despite resolution of symptoms most participants showed Ct levels <30 at day 9. No significant differences were observed for viral load and time to viral clearance between BA.1, BA.1.1 and BA.2 infected individuals. ConclusionWe report a high incidence of omicron infection despite recent booster vaccination in triple vaccinated individuals. Increasing levels of vaccine-induced spike-specific WT antibodies entail increased protection against infection and reduce viral load if infected. High viral load and secretion of live virus for up to nine days may facilitate transmission in a triple vaccinated population.