A case series of severe breakthrough infections observed in nine patients with COVID-19 in a southwestern German university hospital

Vaccination is the key element for protection against COVID-19. Increased vaccination breakthroughs raise the question of whether additional prevention is necessary in case of individual risk factors for a severe course with hospitalization or death despite vaccination.Since July 13, 2021, there is an extended reporting requirement by German law. We analyzed our hospitalized patients with vaccine breakthrough infection during the first 8 weeks.Nine of 67 patients (13.4%) hospitalized for COVID-19 (median age 75 years) were fully vaccinated. Five of these patients received intensive care; two patients died. All had received two doses of BNT162b2 vaccines (Pfizer-BioNTech). There was a median of 99 days between complete immunization and symptom onset. All patients suffered from ≥ three comorbidities. Six patients (66.7%) showed a negative Anti-SARS-CoV-2-N titer at the time of vaccine breakthrough, five of these also had Anti-SARS-CoV-2-S titers 100 U/ml. All determinable cases were Delta variant B.1.617.2.Advanced age, underlying cardiorespiratory disease, and the Delta variant of SARS-CoV-2 were associated with hospitalization of our patients, suffering from vaccine breakthrough infection. Avoidance of face masks, lack of immunization of close contacts, and travel to high-risk areas have been observed as modifiable behavioural circumstances. Consistent personal protective measures, vaccination of close caregivers, and increased awareness might be effective measures in addition to COVID-19 booster vaccination for patients at a high risk to suffer a severe course of infection.