Pfizer vaccine effectiveness dropped 56% for 5-11 year old children

March 1, 2022

A new study from the New York State Department of Health and published in a medRxiv preprint found that from December 13, 2021, to January 30, 2022, among 852,384 fully vaccinated children 12-17 years and 365,502 children 5-11 years, Vaccine effectiveness (VE) against cases declined from 66% to 51% for those 12-17 years and from 68% to 12% for those 5-11 years.

In the Omicron era, the effectiveness against cases of the Pfizer BNT162b2 vaccine declined rapidly for children, particularly those 5-11 years. However, vaccination of children 5-11 years was protective against severe disease and is recommended. These results highlight the potential need to study alternative vaccine dosing for children and the continued importance layered protections, including mask wearing, to prevent infection and transmission.

In New York State (NYS), nearly 850,000 children ≤17 years have been diagnosed with COVID-19. Randomized trails and observational studies conducted during the Delta and earlier variants’ predominance, indicate the BNT162b2 vaccine, developed to protect against original strains, is safe and effective in preventing COVID-19 outcomes in those 5-17 years and older. 1-10 Compared to children 12- 17 years, who receive two 30mg doses, less is known known about real-world vaccine effectiveness against infection and hospitalization effectiveness for children 5-11 years, who receive two 10mg doses, particularly after the Omicron variant’s emergence.

Researchers examined the effectiveness of vaccination during the Omicron variant surge that began in early December 2021 on infection and hospitalization among children 5-11 years compared to 12-17 years using NYS statewide surveillance systems.

During the January 24-30 week, VE for children 11 years was 11% and for those age 12 was 67%. VE against hospitalization declined changed from 85% to 73% for children 12-17 years, and from 100% to 48% for those 5-11 years. Among children newly fully vaccinated December 13, 2021 to January 2, 2022, VE against cases within two weeks of full vaccination for children 12-17 years was 76% and by 28-34 days it was 56%. For children 5-11, VE against cases declined from 65% to 12% by 28-34 days.

The finding of markedly lower VE against infection for children 11 years compared to those 12 and 13 years, despite overlapping physiology, suggests lower vaccine dose may explain lower 5-11 years VE. Children 12 years had the highest VE of all ages, potentially due to being small size relative to dose and more recent vaccination (by 6 weeks on average) than those 13-17 years.

This gap suggests a threshold effect between the two BNT162b2 vaccine doses and need for study of numbers of doses, amount per dose, dose timing, and/or antigens targeted for children 5-11 years.

At this time, efforts to increase primary vaccination coverage in this age group, which remains <25% nationally, should continue. Given rapid loss of protection against infections, these results highlight the continued importance of layered protections, including mask wearing, for children to prevent infection and transmission.

medRxiv report

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