Infected, Unprotected

Study finds previous COVID-19 infection doesn’t protect children from omicron

Rear view of a child with backpack and mask on facing a schoolyard
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This article is part of Harvard Medical School’s continuing coverage of COVID-19.

Fewer than 10 percent of children who contracted COVID-19 in 2020 or early 2021 developed antibodies that can fight off the omicron variant of SARS-CoV-2, according to a new study led by researchers at Harvard Medical School, Boston Children’s Hospital, and the U.S. Food and Drug Administration.

The findings, published May 27 in Nature Communications, echo studies of adults showing that contracting COVID-19 once doesn’t guarantee antibody protection from repeat infection.

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“I hear parents say, oh, my kid had COVID last year,” said co-senior investigator Adrienne Randolph, HMS professor of anaesthesia and of pediatrics at Boston Children’s. “But we found that antibodies children produced during prior infections don’t neutralize omicron. This means that unvaccinated children are still susceptible to omicron.”

Vaccination provides children and teens with better protection against the omicron variant than natural infection, Randolph said.

Loss of antibody protection

The study drew on Overcoming COVID-19, a nationwide study Randolph launched in 2020 that involves 70 children’s hospitals. Some data also came from Boston Children’s Taking On COVID-19 Together Group.

The researchers studied blood samples from children and adolescents who had COVID-19 or multisystem inflammatory syndrome in children (MIS-C) during 2020 and early 2021, before omicron emerged.

Of these, 62 had been hospitalized with severe COVID-19 and 65 with MIS-C. Another 50 children had recovered from mild COVID-19 and hadn’t been hospitalized.

In the laboratory, the team exposed the children’s blood samples to a pseudovirus, which is derived from SARS-CoV-2 but stripped of its virulence. The researchers then measured how well antibodies in the samples were able to neutralize five different variants of concern: alpha, beta, gamma, delta, and omicron.

Overall, children and adolescents showed some loss of antibody neutralization against later-emerging variants—but the loss was most pronounced for omicron.

“Omicron is very different from previous variants,” said Randolph. “It has many mutations on the spike protein, and we now know that this enables it to evade the antibody response.”

Vaccine benefit

When the researchers looked at the children’s history of vaccination, they found that those who had received two doses of COVID-19 vaccine had higher levels of neutralizing antibodies against all five variants, including omicron.

“With the emergence of omicron, vaccination offers children and teens better protection against COVID-19,” said Randolph.

She hopes these findings will encourage parents to get their children and teens vaccinated. According to data from the CDC, only 29 percent of 5- to 11-year-olds and 59 percent of 12- to 17-year-olds had received two vaccine doses as of June 1, 2022. (An FDA panel is expected to meet on June 15 to consider authorization of COVID-19 vaccines for children under age 5.)

One limitation of the study is that it was able to test only for antibody responses, not other measures of immunity such as production of T cells. Because those are much harder to test for, researchers rely on antibody tests to understand people’s level of immunity.

Surender Khurana of the FDA was co-senior author of the paper. Co-first authors were Juanjie Tang and Gabrielle Grubbs of the FDA; Tanya Novak, HMS instructor in anaesthesia at Boston Children’s; and Julian Hecker, HMS instructor in medicine at Brigham and Women’s Hospital.

This research was funded by the U.S. FDA (Perinatal Health Center of Excellence grant GCBER005), U.S. Centers for Disease Control and Prevention (contract 75D30120C07725), and National Institutes of Health (grants R01AI084011, K23HL150244, K23HD096018, and K23HL146936).

Adapted from a Boston Children’s blog post.