A study by researchers in the US has concluded that BNT162b vaccination given to children aged 5 to 11 years reduced the risk of Omicron-associated hospitalisation by more than two-thirds but was less effective against hospitalisation among adolescents.
BNT162b2 vaccination in 12 to 15-year-old recipients has been shown to have a favourable safety profile, produce a greater immune response than in young adults and be highly effective against COVID-19. Nevertheless, data on vaccine effectiveness have only been assessed up to 3 months post-vaccination and the available data preceded circulation of the Omicron COVID-19 variant. Furthermore, there are limited data on the effectiveness of vaccines in younger children, although one study has indicated that vaccination against laboratory-confirmed COVID-19-associated hospitalisation among children aged 5-11 years was 74%, and between 14 and 67 days after a second dose, although this estimate had wide confidence interval (–35% to 95%) that included zero.
For the present study, the US team set out to determine the duration of protection from BNT162b vaccination in adolescents during different periods of time in which the Delta and Omicron were the dominant circulating strains. They also examined the protection of the vaccine against hospitalisation in children aged 5 to 18 years of age infected with the Omicron variant.
The team used a case-control, test-negative design to assess BNT162b effectiveness against COVID-19-related hospitalisation and against critical illness. The researchers also included a group of control patients who were in the same age categories and defined as hospitalised individuals who tested negative for COVID-19 and with no recognised symptoms of the virus. The effectiveness of BNT162b vaccination was assessed after 2 to 22 weeks and after longer than 22 weeks.
BNT162b vaccination and COVID-19
Among those hospitalised aged 12 – 18, there were 918 case patients with a median age of 16 years (50% female), of whom 78% had at least one underlying health condition. In addition, there were 267 case patients with a median age of 8 years (43% female) and of whom 82% had at least one underlying health condition.
Overall among the 1185 cases (i.e., 267 and 918), 25% had critical COVID-19, 14 of whom died. In the 12 to 18 group (918 cases), 27% had critical COVID-19 and 13 died. In the 5 – 11 group (267 cases), 16% had critical COVID-19, one of whom died.
The effectiveness of BNT162b vaccination against COVID-19-associated hospitalisation among adolescents was 92% during the Delta period, 2 to 22 weeks after vaccination and 92% between 23 and 44 weeks post-vaccination. However, during the omicron period, vaccine effectiveness was only 40% against COVID-19-associated hospitalisation, 2 to 22 weeks after vaccination and dropped slightly to 38% between 23 and 44 weeks post-vaccination. Nevertheless, during the Omicron period, vaccine effectiveness was 79% against critical COVID-19 but only 20% against non-critical illness.
Among those aged 5 – 11 years of age, vaccine effectiveness against COVID-19-associated hospitalisation was 68% during the Omicron period, a median of 34 days after vaccination.
The authors concluded that vaccination in children aged 5 to 11 years reduced the risk of COVID-19-associated hospitalisation by two-thirds during the Omicron period adding that while vaccination was less effective in adolescents during the omicron period, it was still able to prevent critical illness.
Price AM et al. BNT162b2 Protection against the Omicron Variant in Children and Adolescents N Engl J Med 2022