As Covid-19 tears across the country, health experts have been calling for increased access to testing that will help track and contain the virus’s swift and often silent spread.
But some of the cheapest and most convenient diagnostic tools on the market might not perform as promised in a crucial contingent of the population, in which they were already being used: children, whose pint-size bodies might make the coronavirus more difficult to detect.
A small but growing body of evidence, some of which has not yet been published in a peer-reviewed scientific journal, suggests that some rapid tests for the coronavirus may falter in very young people, letting low-level infections slip by unnoticed.
In a recent study of more than 1,600 people in Massachusetts, Binax NOW, a rapid test manufactured by Abbott Laboratories, caught 96.5 percent of the coronavirus infections found by a more accurate laboratory test in adults with symptoms. But the rapid test detected just 77.8 percent of the symptomatic cases in people 18 or under. Among people without symptoms, the test faltered further, identifying 70.2 percent of adults and 63.6 percent of children.
Another recent paper, published in November in Clinical Microbiology and Infection, found that a different rapid test by Abbott, called the PanBio, identified just 62.5 percent of coronavirus cases in people 16 or younger, compared with 82.6 percent of infections in adults, although the number of pediatric samples tested was small.
Children rarely seem to have serious cases of Covid, and the youngest among them may also be less likely to pass the coronavirus on to others. But the new findings should encourage more in-depth studies of diagnostic tools for the virus in pediatric populations, health experts said.
“At this moment, I think it’s still totally possible that these tests perform the same way” in children as they do in adults, said Dr. Nira Pollock, the associate medical director of the infectious diseases diagnostic laboratory at Boston Children’s Hospital and one of the researchers who led the Massachusetts study. But without solid data demonstrating how coronavirus diagnostics perform in children, she added, it would be a mistake to assume that young people will test as easily as adults.
Nonetheless, the tests’ performance seems to have been taken for granted. The Binax NOW, which received an emergency green light from the Food and Drug Administration in August, was not tested in anyone younger than 22 before Abbott sought the federal agency’s authorization. Yet the government has already purchased millions of these tests and begun to distribute them to governors and vulnerable communities, encouraging their use in schools as screening tools.
Another of Abbott’s rapid tests, ID NOW, also excluded people 21 and younger from early studies, but it has already appeared in clinics across the country. And a widely used rapid test called the Veritor, made by Becton, Dickinson and Company, was not evaluated in people younger than 18, but it had been publicly optioned for use in schools. Several other rapid testing companies, including Access Bio and LumiraDx, did include a small number of minors in their preliminary studies, but they declined to provide data on performance across age.
In medicine, children are often “assumed to be just miniature versions of grown-ups,” said Jennifer Dien Bard, director of the clinical microbiology and virology laboratory at Children’s Hospital Los Angeles. “But they are not just small adults. It’s really important that any testing that is available, that there are specific strategies offered for children and their specific needs.”
In the rush to clear treatments, vaccines and diagnostics for widespread use, companies often neglect to include children in early trials that test whether products or therapies are safe and effective. But tests for viruses, bacteria and other infectious microbes that yield stellar results for adults do not always translate perfectly for children.
The reasons behind these differences are not always obvious, Dr. Pollock said. For instance, children’s immune systems might be better at homing in on and sequestering certain infectious invaders, making them harder to detect with standard-issue tests.
In one study, published in the Journal of Clinical Microbiology in October, Dr. Pollock and her team amassed data from nine pediatric hospitals across the country, all of which reported relatively scant counts of the virus in children without symptoms. Another, which has not yet been published in a peer-reviewed scientific journal, hinted at a similar trend in children who were sick.
Confused by the terms about coronavirus testing? Let us help:
- Antibody: A protein produced by the immune system that can recognize and attach precisely to specific kinds of viruses, bacteria, or other invaders.
- Antibody test/serology test: A test that detects antibodies specific to the coronavirus. Antibodies begin to appear in the blood about a week after the coronavirus has infected the body. Because antibodies take so long to develop, an antibody test can’t reliably diagnose an ongoing infection. But it can identify people who have been exposed to the coronavirus in the past.
- Antigen test: This test detects bits of coronavirus proteins called antigens. Antigen tests are fast, taking as little as five minutes, but are less accurate than tests that detect genetic material from the virus.
- Coronavirus: Any virus that belongs to the Orthocoronavirinae family of viruses. The coronavirus that causes Covid-19 is known as SARS-CoV-2.
- Covid-19: The disease caused by the new coronavirus. The name is short for coronavirus disease 2019.
- Isolation and quarantine: Isolation is the separation of people who know they are sick with a contagious disease from those who are not sick. Quarantine refers to restricting the movement of people who have been exposed to a virus.
- Nasopharyngeal swab: A long, flexible stick, tipped with a soft swab, that is inserted deep into the nose to get samples from the space where the nasal cavity meets the throat. Samples for coronavirus tests can also be collected with swabs that do not go as deep into the nose — sometimes called nasal swabs — or oral or throat swabs.
- Polymerase Chain Reaction (PCR): Scientists use PCR to make millions of copies of genetic material in a sample. Tests that use PCR enable researchers to detect the coronavirus even when it is scarce.
- Viral load: The amount of virus in a person’s body. In people infected by the coronavirus, the viral load may peak before they start to show symptoms, if symptoms appear at all.
Laboratory tests, such as those that use a technique called polymerase chain reaction, or P.C.R., are sensitive enough to uncover these low-level infections, Dr. Pollock said. But the virus may not be present in high enough amounts to be discovered by a rapid test, such as those that detect only relatively large quantities of antigens, or bits of coronavirus proteins. The Binax NOW is one such test.
Many such children “are going to be negative on rapid tests,” Dr. Pollock said. “That impacts how we think about school settings and day care.”
It may be that some children are naturally predisposed to harbor less of the virus. It was also possible that the children in these studies were all sampled too late in their infections, when the virus had already petered out. If that was the case, Dr. Pollock said, these children might have once carried or even transmitted the virus in large amounts, but they were not tested during that time. Teasing apart these scenarios may be difficult without testing many more children, she said.
For now, “if your goal is to detect infection, molecular tests are the way to go,” she said, referring to laboratory diagnostics like those that use P.C.R.
Still, if children truly do carry around less of the virus, it may be acceptable that some cases are missed by certain tests, said Dr. Ibukun Akinboyo, a pediatrician and infectious disease expert at Duke University in Durham, N.C. “It depends on the goal of testing,” Dr. Akinboyo said. People who carry less of the virus may be less likely to transmit it to others, for instance.
In response to the recent findings out of Massachusetts, Kimberly Modory, a spokeswoman for Abbott, noted that Binax NOW “is for use within seven days of symptom onset” and that the test performed “well” in this window of time. She pointed out that if symptomatic children who were carrying low amounts of the virus — a group the company argued were less likely to be infectious — were discarded from the data set, the test’s performance increased. Abbott declined to comment on the findings among asymptomatic people, noting the company was conducting its own studies on the matter.
But several experts caution that tests alone cannot determine whether someone is contagious, or rule out the risk of passing a pathogen to others. Harboring less of the virus in your nose does not necessarily mean you pose less of a transmission risk, especially in an understudied population like children, Dr. Dien Bard, of Children’s Hospital Los Angeles, said. “These people can very well still be infectious.”