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Rapid COVID-19 tests are highly accurate for kids, study finds

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While PCR tests for COVID-19 have become the "gold standard" in detecting the virus, a new study says rapid tests are highly accurate when it comes to children and teens.

The study, led by researchers from Johns Hopkins School of Medicine in collaboration with other institutions and published in MedRxiv, shows that rapid tests given to adolescents at school or at home has a similar accuracy to PCR tests.

Rapid tests, also known as "antigen" or "lateral flow" tests, return faster results, are less sensitive than PCR tests. PCR tests have been used for years to diagnose a variety of diseases and uses a molecular testing process in which a nasal or throat swab is mixed with chemical ingredients to needed to create copies of the genetic material that makes up the virus. 

In rapid antigen tests, samples from patient swabs are mixed with a buffer, a liquid that helps the virus travel across a strip coated with antibodies that bind to specific proteins — known as antigens — common to many variants of the virus. Similar to a positive over-the-counter pregnancy test, the strip appears as a colored line if it detects the antigen.

The researchers, which studied 1,000 children and teens under the age of 17, found the rapid antigen test sensitivity rate was 92.7%, meaning it identified cases the PCR test also identified. Its specificity rate was 98%.

All of the children were given the BinaxNOW rapid antigen test manufactured by Abbott Laboratories at Baltimore Convention Center in 2021, when the Delta variant was prevalent, according to the study.

There was only a slight difference in the sensitivity of the test for children with symptoms and without symptoms. The study has not been peer-reviewed, but it suggests that rapid tests can be confidently used.

The study also found that the test's ability to determine a negative, known as a negative predictive value or NPV, was also high – 99.2% of those who tested negative for COVID-19 were actually negative. "The near 100% NPVs for both symptomatic and asymptomatic children, including some children with recent high-risk exposures, should provide providers and parents with assurance that a negative rapid antigen test with this product can be trusted," the researchers write.

Because schools can be disrupted by COVID-19 cases and vaccines are not yet available for children 5 and under, "testing may improve the ability for children to remain in in-person activities, minimizing absences from school and extracurriculars," the researchers say. "Highly accurate rapid antigen tests may be vital to containing future COVID-19 waves while mitigating detrimental effects."

Zishan Siddiqui, principal investigator and the senior author of the study, told CBS News the researchers want "to caution that a negative rapid antigen test in children and adolescents should not be taken as a license to abandon other COVID-19 safety measures such as physical distancing, masking, frequent hand-washing and maintaining good ventilation."

"If used for asymptomatic screening, this should be considered an additional tool to supplement the existing safety measures," said Siddiqui, who is chief medical officer of the Baltimore Convention Center Field Hospital Task Force.

"Our finding also provides support for the use of rapid tests in implementing 'test-to-stay' strategies, where exposed schoolchildren are enabled to continue uninterrupted in-person learning while being tested frequently after exposure," Siddiqui said.

Alexander Tin contributed to this report.

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