September 15, 2022
Danyu Lin, PhD, Dennis Gillings Distinguished Professor of Biostatistics at the UNC Gillings School of Global Public Health, led research recently published in the New England Journal of Medicine (NEJM) that assesses the level of immunity conferred by COVID-19 vaccination or previous SARS-CoV-2 infection among children. The findings provide crucial information for making decisions about vaccine boosters for children.
The emergence of new variants of SARS-CoV-2, the virus which causes COVID-19, especially the currently dominant Omicron variant, has raised important questions about the level of immunity conferred by COVID-19 vaccination and/or previous infection with SARS-CoV-2 and the durability of that immunity. These questions are especially pertinent to decisions about additional, “booster,” doses of vaccine.
In a recent NEJM article titled “Effects of Vaccination and Previous Infection on Omicron Infections in Children,” Lin and colleagues report findings from a cohort study that addresses these questions, shedding light on the degree of immunity children maintain in response to COVID-19 vaccination or/and previous infection with SARS-CoV-2.
Emergency use authorization of the Pfizer–BioNTech vaccine (BNT162b2) for 5–11-year-olds in late October 2021 made it the first COVID-19 vaccine available to children in the United States. An efficacy study found the vaccine 90.7% effective in preventing disease in that age group. However, the spread of the Omicron (B.1.1.529) variant of SARS-CoV-2, which proved adept at evading previously established immunity, in the following weeks raised new questions about the level of risk children face from COVID-19.
Lin worked with doctoral students Yu Gu and Yangjianchen Xu as well as Donglin Zeng, PhD, professor of biostatistics at the Gillings School, and epidemiologists from the N.C. Department of Health and Human Services: Bradford Wheeler, MPH, Hayley Young, MPH, Shadia Khan Sunny, MD, PhD, MPH, and Zack Moore, MD, MPH. The team conducted a cohort study to provide an updated understanding of children’s risk of infection, hospitalization and death from COVID-19. Their article was published online on September 7 and will appear in the September 22 print issue of the NEJM.
The researchers used the North Carolina surveillance data on 887,193 children ages 5–11 years for whom information on vaccination, SARS-CoV-2 infection, hospitalization and death was collected. Using an extension of the Cox regression model, the study team formulated the effects of the BNT162b2 vaccine and previous infection with SARS-CoV-2 on the rate of subsequent infection during the spread of Omicron.
They found that two doses of vaccine provided effective protection, but that protection waned over time, and very significantly, during a time that coincided with the spread of the Omicron variant. Among previously uninfected children, vaccine effectiveness reached 63% at 4 weeks after the first dose and decreased to 16% at 16 weeks; among previously infected children, vaccine effectiveness reached 70% at 4 weeks after the first dose and decreased to 22% at 16 weeks. Among unvaccinated children, the estimated effectiveness of omicron infection against reinfection with omicron was 91% at 2 months and 63% at 4 months; among vaccinated children, the estimated effectiveness of omicron infection alone against reinfection with omicron was 94% at 2 months and 79% at 4 months.
“Both the BNT162b2 vaccine and previous infection were found to confer considerable immunity against omicron infection and protection against hospitalization and death,” writes Lin. “The rapid decline in protection against Omicron infection that was conferred by vaccination and previous infection provides support for booster vaccination.”
On September 2, the N.C. Department of Health and Human Service announced that updated versions of the Pfizer-BioNTech and Moderna vaccines would soon be available as boosters for people 12 years of age and older. In a Daily Tarheel article about the announcement, Lin emphasizes the stakes involved.
“The people who don’t get boosted, their chances of getting infected are higher [than those who get boosted], and their chances of being hospitalized or dying are much, much higher,” he said. In an article that is currently in press at a major medical journal, Dr. Lin’s team reports findings on the effectiveness of boosters against Omicron infection and severe outcomes.
Lin sat down with Josh Kelety, a reporter for the Associated Press, to address disinformation about these findings. Read his response.