Rapid Covid home tests are more likely to give a false negative with the heavily-mutated Omicron variant compared to earlier strains, the US Food and Drug Administration (FDA) said Tuesday.
The news comes as the country is facing a massive surge in cases that experts say is being under-captured as a result of a testing crunch, with long wait times for the more accurate PCR tests, and home kits in extremely short supply.
In a statement, the FDA said it was collaborating with the National Institutes of Health (NIH) to study the performance of home tests, also known as “antigen” tests, against patient samples containing live versions of the Omicron variant.
“Early data suggests that antigen tests do detect the Omicron variant but may have reduced sensitivity,” the agency said.
Sensitivity is a measure of how likely a test is able to detect a positive.
Previous testing had focused on heat-inactivated virus samples, rather than live virus which is better, and a drop-off in performance hadn’t been spotted until now, the statement added.
The FDA said it would continue to authorize the use of antigen tests — which work by detecting surface proteins of the coronavirus — and that individuals should continue to use them in accordance with the instructions.
For instance, some rapid tests instruct users to take two tests, a certain amount of time apart, in order to confirm a negative.
If a person tests negative with a rapid test but is thought likely to have Covid, either because of symptoms or their exposures, they are still recommended to get a “gold standard” molecular test — such as PCR.
These detect the genetic material of the virus. They are more accurate because they can make millions of copies of the virus’ RNA, so even tiny amounts become detectable.
Meanwhile, Quebec, the second most populous Canadian province, has “no choice” but to allow some essential workers to continue working even after testing positive for COVID-19 to prevent staff shortages from impeding its healthcare services, Health Minister Christian Dube said Tuesday.
Quebec, which has been setting daily records since the Omicron variant started a new wave of rapidly rising infections, recorded 12,833 new cases on Monday – the highest one-day count of any region in Canada during the pandemic.
“Omicron’s contagion is so exponential, that a huge number of personnel have to be withdrawn – and that poses a risk to the network capacity to treat Quebecers,” Dube told reporters at a briefing.
“We made the decision that under a certain condition positive staff will be able to continue working according to a list of priority and risk management,” he said, adding that more information would be provided in the coming days.
Dube said Quebec would also offer a third dose of a COVID-19 vaccine to everyone above the age of 18 from Jan. 4. Last week, Quebec ordered bars, gyms and casinos to shut and directed people to work only from home. It also limited the size of gatherings at private homes and restaurants to six people