British health officials said Friday that 43,000 people may have been wrongly told they don’t have the coronavirus because of problems at a private laboratory. The UK Health Security Agency said the Immensa Health Clinic Ltd. lab in Wolverhampton, central England, has been suspended from processing swabs after the false negatives.

Will Welfare, the agency’s public health incident director, said it was working “to determine the laboratory technical issues” behind the inaccurate tests. The issue was uncovered after some people who were positive for Covid-19 when they took rapid tests went on to show up as negative on more accurate PCR tests.