With new variants, COVID-19 vaccination is mildly effective in children
With new variants, COVID-19 vaccination is mildly effective in children

With new variants, COVID-19 vaccination is mildly effective in children

COVID-19 variants such as Delta, Omicron and “DeltacronSubvariants have been shown to be particularly effective in causing breakthrough infections in fully vaccinated individuals. However, the vaccines still provide lasting protection against serious illness, hospitalization and death.

The Pfizer BioNTech vaccine was approved for children months after adults were eligible for COVID-19 vaccination. In combination with the U.S. Centers for Disease Control and Prevention (CDC), researchers from the University of Arizona Health Sciences investigated how effective COVID-19 vaccination was in preventing infection and serious illness in children and adolescents.

The study, published in the CDCs Weekly report on morbidity and mortality (MMWR), was performed from 25 July 2021 to 12 February 2022, with Delta and then Omicron being the dominant COVID-19 variant.

The actual data were collected from the CDC’s PROTECT study, which tested participants aged 6 months-17 years each week in Arizona, Texas, Florida and Utah. Legal guardians provided information about participants’ health, demographics, vaccination history, and previous COVID-19 infection history. Infants, children, and adolescents submitted a weekly examination and nasal swab for PCR testing and genome sequencing.

The study cohort included 1364 participants, of which 77% (n = 1052) were children aged 5-11 years and 23% (n = 312) of them were young 12-15 years. Overall, 76% of participants were from Arizona, 52% were women, 75% were white, 34% were Hispanic, and 10% had 1 or more chronic medical conditions.

Participants who received 1 or more doses of the Pfizer-BioNTech vaccine (the only vaccine approved for children and adolescents) reported wearing a mask for 84% of school time and 70% of community hours. Unvaccinated children and adolescents reported a grade for 60% of school time and 48% of community hours. Several COVID-19 cases occurred in participants who wore one mask smaller.

A total of 381 COVID-19 infections were recorded among children 5–11 years of age, and there were 127 infections among adolescents 12–15 years of age. 93% (n = 352) of the children’s infections and 76% (n = 97) of the young people’s infections were Omicron.

Among children aged 5-11, 65% (n = 682) received 2 vaccine doses, 7% (n = 69) received 1 dose, and 29% (n = 301) were unvaccinated. Among the 12-15-year-olds, 68% (n = 212) received 2 vaccine doses, 5% (n = 15) received 1 vaccine, and 27% (n = 85) were unvaccinated.

There were 186 breakthrough infections among the vaccinated participants, of which 37.6% were asymptomatic. Of the 252 COVID-19 infections among unvaccinated participants, 44% (n = 112) were asymptomatic. Non-vaccinated participants were more likely to be asymptomatic under Omicron (49%) than under Delta (60%). Overall, 51% of Omicron infections were asymptomatic and 34% of Delta infections were asymptomatic.

Vaccination with 2 doses of the Pfizer-BioNTech vaccine reduced the risk of Omicron infection by 31% in children aged 5-11 years and by 59% in adolescents aged 12-15 years. This was a marked decrease compared to the Delta period, when the protection against infection was 87% in adolescents (children were not yet approved to receive the vaccine).

The study authors concluded that 2 doses of the Pfizer-BioNTech COVID-19 vaccine were effective in preventing symptomatic and asymptomatic infections in participants aged 5-15 years. Vaccine efficacy was highest against Delta in the adolescent cohort (12-15 years) and lowest against Omicron in pediatric participants (5-11 years).

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