Breakthrough COVID-19 cases
Breakthrough COVID-19 reported by participants would be monitored for 3 years after vaccination. In early 2022, Hong Kong had its first major wave of COVID-19, dominated by the Omicron BA.2.2 variant. Seven participants, in the humoral (n=5), combined (n=1) and dysregulation (n=1) categories, had reported COVID-19 during that time after a partial or complete primary series (Table 1). All participants reported mild infections without need for hospitalization. Contingency analyses by Fisher exact test showed that proportion of infected participants did not differ by vaccine brand (B 15% vs C 21%, P=0.69), age group (adults 15% vs children 21%, P=0.69) or disease category (humoral 29% vs non-humoral 9%, P=0.21). Immunogenicity assessments were available for 3 of them pre- and post-infection (patients 13, 22, and 26), all of whom were seronegative for S-RBD IgG both immediately before and after infection (Tables 2 and 3).