Vaccine efficacy also declined from 66 per cent to 51 per cent for those between 12 and 17 years.
Although vaccination was found protective against severe disease the efficacy against hospitalization also declined from 85 per cent to 73 per cent for children aged between 12 and 17 years, and from 100 per cent to 48 per cent for those aged between 5 and 11 years.
The difference in effectiveness may be explained by “lower vaccine dose”, said the researchers.
Compared to children 12-17 years, who received two 30g doses,children 5-11 years, received two 10g doses.
The study examined Pfizer vaccine effectiveness from December 13, 2021 to January 30, 2022, among 852,384 fully-vaccinated children 12-17 years and 365,502 children 5-11 years.
Among children 12-17, protection declined substantially, albeit more slowly than observed among younger children.
Within just two weeks of full vaccination the efficacy for children aged 5-11 dropped to 65 per cent and by 28-34 days it was 12 per cent
For children between 12-17 years, effectiveness declined from 76 per cent to 56 per cent by 28-34 days.
“These results highlight the potential need to study alternative vaccine dosing for children and the continued importance of layered protections, including mask wearing, to prevent infection and transmission,” she added.
The study comes as several states and the US Centers for Disease Control and Prevention have eased the mask restrictions.
Source: IANS
