Outbreak investigation of symptomatic SARS-COV-2 VOC 202012/01-lineage B.1.1.7 infection in healthcare workers, Italy

Loconsole, Daniela; Sallustio, Anna; Accogli, Marisa; Leaci, Angela; Sanguedolce, Antonio; Parisi, Antonio; Chironna, Maria

OBJECTIVES: In December 2020, Italy began a national immunization campaign using the BNT162b2 mRNA COVID-19 vaccine, prioritizing healthcare workers (HCWs). Immune serum from vaccinated subjects seems to (largely) retain titres of neutralizing antibodies, even against SARS-CoV-2 VOC 202012/01-lineage B.1.1.7. Here, we describe an outbreak of SARS-CoV-2 lineage B.1.1.7 infection in three HCWs in a hospital setting; two of the HCWs were fully vaccinated (i.e., had received two doses). METHODS: Two physicians and one nurse working on the same shift on February 20, 2021, were involved in the outbreak. Real-time PCR, antigen tests, and serological tests for the IgG anti-spike protein of SARS-CoV-2 were performed, along with whole-genome sequencing (WGS). RESULTS: SARS-CoV-2 infection was confirmed in all three HCWs; all presented with mild symptoms of COVID-19. The two physicians were fully vaccinated with BNT162b2 vaccine, with the second dose administered 1 month before symptom onset. Both had high titres of IgG anti-spike antibodies at the time of diagnosis. WGS confirmed that all virus strains were VOC 202012/01-lineage B.1.1.7, suggesting a common source of exposure. Epidemiological investigation revealed that the suspected source was a SARS-CoV-2-positive patient who required endotracheal intubation due to severe COVID-19. All procedures were carried out using a full suite of personal protective equipment (PPE). CONCLUSIONS: This mini-outbreak highlights some important issues about the efficacy of vaccines against transmission of SARS-CoV-2 variants, the high risk of exposure among HCWs, and the need for optimized implementation of PPE in hospitals. The wide circulation of VOC 202012/01 in Europe and Italy highlights the need to improve surveillance and genetic sequencing.