Hundreds of thousands of Moscow’s rapid antibody tests labeled as Dutch-made are unreliable at detecting the coronavirus in its early stages, meaning patients who receive false negatives could potentially infect others, a new investigation has said.

The tests are sold under the brand name Biozek by Dutch manufacturer Inzek International Trading, according to the Organized Crime and Corruption Reporting Project (OCCRP) and Russia’s Important Stories investigative website. Biozek is one of at least three brands of rapid coronavirus tests released by European and U.S. manufacturers that are in fact relabelings of a popular Chinese model.

Russia is among Inzek’s largest customers, OCCRP reported, with its health services and government authorities using the rebranded Chinese tests. 

Moscow’s city administration has purchased hundreds of thousands of Biozek tests, Important Stories reported Wednesday. The tests have reportedly been administered to more than 175,000 Muscovites and 50,000 of Moscow’s medics.

A Spanish study said that the Chinese-made test, which claims to have a 92% accuracy rate, gives false negatives more than half the time, OCCRP and Important Stories reported. Its accuracy improves dramatically one month after the onset of Covid-19 symptoms, but the test’s packaging does not mention the one-month lag, OCCRP cited the study’s co-author as saying.

A separate comparative study ranked the Biozek test the least effective of nine commercially available rapid tests.

Inzek’s distributor in Russia, Biotek, told Important Stories that all of its available tests went to a state procurement order and that it was awaiting a new batch.

The unreliable kits, which received approval from the federal health watchdog, have also been used in other coronavirus-hit areas across Russia including the republic of Komi and the Leningrad region. Private clinics have also gotten their hands on the Biozek tests, Important Stories reported.

The outlet tracked down several online retailers that sell the tests to private citizens in violation of safe use guidelines. “They’re made for home conditions,” one of the sellers was quoted as saying.

Experts say that false negative results pose a threat to others in the community.

“A false negative is a disaster,” OCCRP quoted Marien de Jonge, a scientist involved in Covid-19 research at the Radboud University Medical Center in the Netherlands, as saying. 

Russia now has the highest number daily infections in Europe, with more than 10,000 new cases reported each day since Sunday. Russia has confirmed a total of 165,929 coronavirus cases, placing it seventh in the world, as of Wednesday.

Includes reporting from OCCRP.