Rapid antigen test kits have poured into supermarkets, online stores and pharmacies around the world as countries race to keep up with the rapid transmission rate of the Omicron variant, marking a shift towards the self-administered testing of PCR assays, which has long been considered the gold standard for detecting the coronavirus.
But there is no definitive international guideline for the use of antigen testing for Covid-19, and a global patchwork of policy has emerged as each country weighs the benefits and risks of the alternative testing method.
Britain has been using rapid antigen testing to combat outbreaks since 2020, even before Omicron, and makes them available for free. France started selling them through supermarkets late last month. The Biden administration recently said it planned to make 500 million tests available for free and Americans could request that tests be sent to their homes.
Singapore has allowed people to leave the isolation if they get a negative antigen test result after 72 hours. Israel is asking people to swab their throats when using rapid antigen tests, not just their nostrils, to increase the chances of detecting the virus even if it goes against the manufacturer’s instructions.
“There are wildly variable approaches to where, when and how antigen testing is used in different countries,” said Deborah Williamson, a professor of public health at the University of Melbourne in Australia.
The lack of consistency in how antigen testing is deployed raises the question of how the world should control the severity of the pandemic, she said, as some countries identify each individual case and others prioritize serious ones.
In addition, while promising faster results, antigen tests are significantly less reliable at detecting infections than the PCR tests, studies have shown.
The self-swab in a home antigen testing kit, which is intended to reach the inside of the nostril, is less than 30 percent capable of detecting a positive case of coronavirus compared to the nasopharyngeal swab used in a PCR test, which tests the wall at the end of the nasal cavity, said Dr. Kiho Hong, a professor of laboratory medicine at Yonsei University in South Korea.
Accordingly, health experts from the Infectious Diseases Society of America said PCR testing was the preferred method of diagnosing a Covid-19 infection. But they added that antigen testing could help identify cases where PCR testing was not readily available.
A shortage of PCR tests in countries like the United States and Australia has also left some people waiting hours in line and several days to get the result. That led Australian officials to order people with no Covid symptoms to undergo a PCR test only if they had received a positive antigen test result.
Demand for antigen testing has become so overwhelming in Australia that the government began banning price hikes on the tests last week, saying it would limit the number of people people can buy. And the state of New South Wales has ordered residents to report their positive rapid antigen test results from January 19. Those who do not follow the rules will be fined 1,000 Australian dollars (approximately $720).
“Omicron has been a game changer,” said Professor Williamson, adding that it “really catalyzed the shift to large-scale rapid antigen testing.”
That shift has a pitfall, she added: Governments could lose their ability to track new variants and the extent of the virus’ spread, as the shift to self-testing won’t yield all the results.
In addition, Professor Williamson said that with the Omicron variant in many countries it is no longer realistic to keep track of every single case.