Rapid antigen test kits have poured into supermarkets, online stores and pharmacies around the world as countries race to keep up with the rapid transfer of the Omicron variant, marking a shift to self-administered tests from the PCR test, which has long been considered the gold standard for detecting the coronavirus.
But there are no definitive international guidelines for the use of antigen tests for Covid-19, and a global patchwork of policies has emerged as each country weighs the advantages and risks of an alternative testing method.
Britain has used rapid at-home antigen tests to fight the outbreak since 2020, even before Omicron was used, and made them freely available. France began allowing supermarkets to sell them late last month. The Biden administration recently said it plans to make 500 million tests available for free and that Americans can order the tests sent home.
Singapore allowed people to leave isolation if they received a negative antigen test result after 72 hours. Israel requires people to clear their throats when using rapid antigen tests, not just their nose, to increase the chances of detecting the virus even if it goes against the manufacturer’s instructions.
“There are wildly changing approaches to where, when and how antigen tests are used in different countries,” said Deborah Williamson, professor of public health at the University of Melbourne in Australia.
She said the lack of consistency in how antigen tests are published raises the question of how the world should monitor the severity of the pandemic, when some countries identify each case individually and others prioritize severe cases.
Additionally, while the results of antigen tests promise faster results, they are significantly less reliable in detecting infection than PCR tests, studies have shown.
The self-swab in the home antigen test kit, which aims to get inside the nostril, is less than 30 percent able to detect a positive coronavirus case compared to the nasopharyngeal swab used for PCR testing, which reaches up to 30 percent less than the nasopharyngeal swab used for the PCR test, said Dr. Yonsei University in South Korea, the wall at the end of the nasal cavity.
Accordingly, health experts with the American Infectious Diseases Association said the PCR test was the preferred method for diagnosing Covid-19 infection. But they added that antigen tests can help identify cases where PCR tests were not readily available.
And a shortage of PCR tests in countries such as the United States and Australia has caused some people to wait hours in line and several days for a result. This prompted Australian officials to require people without symptoms of Covid to seek a PCR test only if they receive a positive antigen test result.
Demand for antigen tests has become so overwhelming in Australia that the government last week began banning price gouging in tests and said it would limit the number people can buy. The state of New South Wales has ordered residents to report their positive rapid antigen test results from January 19. Those who do not comply will be fined A$1,000 (about $720).
“Omicron has been a game-changer,” Professor Williamson said, adding that it “has already catalyzed the shift to rapid, large-scale antigen testing.”
There is a quandary in this shift, she added: Governments may lose their ability to track new variables and the extent of the virus’ spread, because switching to self-testing will not capture all results.
In addition, Professor Williamson said, with the Omicron variant, it is no longer realistic in many countries to track each case individually.