Clinical characterization of COVID-19 breakthrough infections, Philippines.

We clinically characterized PCR detected breakthrough infections among partially/fully vaccinated cases with majority given an inactivated vaccine, CoronaVac. From 1 March to 15 July 2021, we detected 182 SARS-CoV-2 infections among vaccinated cases with 129 classified as breakthrough infections. Majority were male, 30-39 y.o., and were asymptomatic or mildly symptomatic with few severe cases. Alpha, Beta and Delta VOCs were detected from sequenced breakthrough infections. Healthcare workers had significantly lower Ct values(higher viral loads) versus non-HCWs. Our results underscore the importance of regular PCR screening for HCWs due to the risk of SARS-CoV-2 transmission from asymptomatic breakthrough infections and provide evidence supporting administration of a booster dose especially to HCWs.