About 1% of kids who visited a Seattle hospital in April had been infected with the novel coronavirus, according to the first large-scale survey for antibodies in children. The study also found most of the youngsters developed a robust immune response, an encouraging sign for a future vaccine.

“If children can respond to the virus, then children can respond to a vaccine,” said Dr. Janet Englund, an infectious disease specialist at Seattle Children’s and co-author of the report. “And vaccines that are given to children are one of the most effective ways to stop the spread of disease in the community.”

Most of the children who tested positive for antibodies had no symptoms of COVID-19, the disease caused by the novel coronavirus. That fits with widespread evidence that children are much less likely than adults to become ill or die.

The analysis has not yet been peer reviewed or published in a scientific journal, and researchers caution it is just a snapshot that doesn’t shed light on two of the most vexing unknowns about the pandemic: the role of children in spreading the virus, and what is likely to happen when schools reopen.

“This is just a baby step,” Englund said. “But this is, to my knowledge, the first study of seroprevalence in children.”

The research team analyzed blood samples from 1,076 children who sought care for any reason at Seattle Children’s hospital in March and April. Most of the visits were for emergencies unrelated to the coronavirus. But the group is not a random sample so the results may not reflect the general population, said lead author Adam Dingens, of the Fred Hutchinson Cancer Research Center.


Ten of the children — one in March and nine in April — had antibodies in their blood. Only two were suspected of being infected and both had tested positive via nasal swabs, which detect virus present during active infection. Three had tested negative on nasal swabs administered as part of routine screening at the hospital.

It generally takes at least two weeks for antibodies to develop, so their presence in the blood indicates an infection sometime in the past.

Since so few children get sick and are tested for the virus, antibody testing will be invaluable — but much more of it is needed, said Sarah Cobey, who studies flu and other pathogens at the University of Chicago and was not involved with the Seattle study.

“This is exactly the kind of information we need to understand the real risks of reopening schools,” she said. “It’s exciting to see any data at all on antibody levels in kids, but I hope we know so much more than this in a couple of months.”

Many of the commercial antibody tests flooding the market are so unreliable as to be worthless. But co-author Jesse Bloom and his colleagues at Fred Hutch have developed a series of highly sensitive and accurate assays to not only detect antibodies but also tease out details about the immune response.

Each positive antibody test is checked against the gold standard in the field: an assay to determine whether the antibodies are powerful enough to neutralize the virus, which is the hallmark of immunity. Two children did not reach that threshold, but it’s possible they were recently infected and hadn’t yet developed a full antibody response, the report points out.


One child’s sample exhibited one of the most potent antibody responses the researchers had ever measured. “We’re still trying to figure out how this infection plays out in both kids and adults and whether there’s likely to be ongoing protection, so it was really exciting to see that,” said Kate Crawford, the graduate research assistant at Fred Hutch who conducted the test.

Some medical experts have argued that since children don’t often get sick from the virus, their immune response might be nonexistent or weak, Englund said. Though the number of children in the Seattle study is small, the results clearly show that’s not the case. She also plans to monitor some children for up to two years to see how long the antibodies last.

Dr. Frank Esper, a pediatric disease specialist at Cleveland Clinic who was not part of the research group, said results from similar antibody surveys in other parts of the country should be released in coming weeks and help provide a more complete, national picture. “This study only relates to the epidemiology of the (Seattle) area, so it’s one piece of the puzzle of what happened in the United States.”

While a dangerous inflammatory syndrome linked to the novel coronavirus has been seen in a handful of youngsters across the state, Department of Health data show no child deaths caused by infection. However, a recent analysis found half of new infections are occurring in people under 40, with children accounting for 11%.

Widespread blood testing for antibodies is just beginning in communities around the world and results vary widely. In New York City, where the American epidemic was most intense, an estimated 20% of adults test positive, while in some California communities it’s less than 3%.

Antibody testing remains rare in Washington. In Western Washington, where social distancing started early, modeling based on death data suggests only about 1.4% of residents had been infected by early May.

That’s roughly on par with the 1% positive rate seen in the children’s antibody tests, which suggests children are getting infected at about the same rate as adults, said Bloom. But that also means most children, like adults, remain susceptible.

“We aren’t by any means done with this virus yet,” Bloom said.