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

High rate of BA.1, BA.1.1 and BA.2 infection in triple vaccinated | medRxiv: Background Booster 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 infections in triple vaccinated individuals are scarce. Methods We conducted a 4-week twice-weekly SARS-CoV-2 qPCR screening shortly after an mRNA vaccine booster in 375 healthcare workers. Anti-Spike IgG levels and neutralization titers were determined at study start. qPCR-positive participants were sampled repeatedly for two weeks and monitored for symptoms. Result In total 82 (cumulative incidence 22%) omicron infections were detected, divided between BA.1, BA.1.1 and BA.2. Only 10% of infected participants remained asymptomatic. 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. While post-booster antibody titers were similar in those with and without subsequent breakthrough infection (p>0.05), high antibody titers were linked to reduced