Asymptomatic SARS-CoV-2 vaccine breakthrough infections in health care workers identified through routine universal surveillance testing

Concerns exist about the efficacy of COVID-19 vaccines against immune escape by viral variants of concern (VOCs): Delta is currently the most common VOC worldwide (1), and nasopharyngeal swabs (NPSs) show that fully vaccinated persons, like unvaccinated persons, harbor infectious viral loads (2). Reports to date have assessed the prevalence of vaccine breakthrough (VBT) infection among health care workers (HCWs), mostly based on spontaneous self-reporting by symptomatic HCWs and hence missing asymptomatic persons, who could nevertheless transmit the pathogen. Once a positive result is identified in an HCW, most countries ask for a 14-day quarantine or 2 consecutive follow-ups after at least 10 days before the HCW is admitted back to the workplace. Such mandatory quarantines can lead to large HCW shortages and cause health crises in hospitals.