Pfizer Vaccine Efficacy in Children and Adolescents During Delta and Omicron

The US Food and Drug Administration (FDA) approved the Pfizer-BioNTech COVID-19 vaccine for children 5 years and older in late October 2021. However, as of mid-March 2022, only about 27% of children had received 2 vaccine doses. This is despite the highly infectious Omicron and Delta variants causing severe disease in children at rates unprecedented earlier in the pandemic.

A new study, published yesterday in The New England Journal of Medicine, examined vaccine effectiveness against critical COVID-19 and hospitalization in children and adolescents.

The case-control, test-negative study enrolled patients from July 1, 2021-February 17, 2022. During this time period, the Delta and then Omicron variants caused the majority of COVID-19 infections. Case patients with COVID-19 and controls without COVID-19 were enrolled from 31 hospitals across 23 US states.

The study utilized data from the national Overcoming COVID-19 Network to recruit child and adolescent case patients. Case patients were identified via reviewing hospital admissions logs and electronic medical records. Those hospitalized with COVID-19 or with clinical symptoms indicative of COVID-19 as the primary reason for admittance were included in the case patient group. The control group was matched to the primary study cohort by hospital of admittance, age category (5-11, 12-15, and 16-18 years), and time of hospital admittance.

The investigators estimated vaccine efficacy by the proportion of patients who were fully vaccinated with 2 doses of the Pfizer-BioNTech vaccine at least 14 days before COVID-19 illness. Pfizer-BioNTech is currently the only COVID-19 vaccine authorized for use in children and adolescents under 18 years of age.

The study enrolled 1185 case patients, 88% of whom had not received a COVID-19 vaccine. Of the case patients, 25% (n=291) had severe COVID-19, including 14 who died. Of the 249 adolescents with critical COVID-19, 93% were unvaccinated. Among the 42 children 5-11 years with critical COVID-19, 93% were unvaccinated.

“We hope our findings will help parents make the decision to vaccinate their children and teens against COVID-19,” said Adrienne Randolph, MD, MSc, a co-leader of the study. “The benefits clearly outweigh the risks, as severe infections in childhood can have long-term consequences.”

During the Omicron-predominant period, December 19, 2021-February 17, 2022, vaccine efficacy was 40% against hospitalization, 79% against critical COVID-19, and 20% against noncritical COVID-19 for adolescents 12-18 years of age. Among the children 5-11 years old, vaccine efficacy against hospitalization was 68%.

Because the Pfizer-BioNTech vaccine was granted Emergency Use Authorization (EUA) for children under 12 on October 29, 2021, there was insufficient data to gauge the vaccine efficacy for children during the Delta-predominant period (July 1, 2021-December 18, 2021). In the adolescent cohort, vaccine efficacy against COVID-19-related hospitalization was significantly higher during the Delta period (92% protection) than during Omicron (40% protection).

During both the Delta and Omicron periods, Pfizer-BioNTech vaccination prevented severe and fatal COVID-19. “The reason for a child to get a COVID-19 vaccine is to prevent severe complications of SARS-CoV-2 infection, including hospitalization,” Randolph concluded. “This evidence shows that vaccination reduces this risk substantially in 5- to 11-year-olds. And while vaccination provided adolescents with lower protection against hospitalization with omicron versus delta, it prevented critical illness from both variants.”