Q&A about China's rapid antigen self-test kits

China has granted approval for five types of COVID-19 antigen kits made by local companies, state broadcaster CCTV said on Saturday.

This follows a guideline on COVID-19 antigen testing issued by the National Health Commission, which stated that rapid antigen self-test kits are now available across China – at pharmacies and on e-commerce platforms.

Hu Bijie, director of the Department of Infectious Diseases, Zhongshan Hospital of Fudan University, and Lu Hongzhou, president of Shenzhen Third People's Hospital, answer some relevant questions.

Q: What's the difference between the antigen test and nucleic acid test? Can the former replace the latter?

Hu: Generally speaking, nucleic acid testing is still the "golden criteria" for COVID-19 infection and is more accurate, while antigen testing is a valuable supplement as it is more convenient.

Nucleic acid testing uses the principles of molecular biology. Through the reverse transcription, amplification and quantitative detection of the nucleic acid sequence of pathogens, this virus detection has higher sensitivity and specificity as well as the accuracy.

Antigen testing uses the principle of immunology and can complete virus detection in a non-laboratory environment quickly. It is an effective supplement to nucleic acid testing, but can not be a replacement.

For example, if the positive rate detected by nucleic acid testing is 100 percent, then it will be around 70 percent if it's an antigen test.

But the nucleic acid testing entails higher costs, such as professional equipment, venues and personnel, and it takes longer time.

The antigen testing can be given anytime and anywhere with simple operation, low cost and quick result.

Q: Under what circumstances can antigen testing be applied?

Hu: Antigen testing can screen out those with a higher viral load and infectiousness. It has its own application scenarios and value.

For people living in distant areas, it's not easy to get nucleic acid testing so the antigen testing is a better choice.

Moreover, in daily life, when residents get a headache or fever and worry if it's a COVID-19 infection, or there are too many people queuing for the nucleic acid test given by medical institutions, they can use the self-test kit at home.

If one is positive in an antigen test, with symptoms or otherwise, he or she should report it to the community and go to a designated medical institution for nucleic acid testing.

During the quarantine and observation period, those quarantined can also perform antigen self-testing once a day as an effective supplement to nucleic acid testing.

Q: Why has China added antigen testing as a supplement to nucleic acid testing?

Lu: The Omicron COVID-19 variant, which has significant immune evasion properties and is more infectious, is now spreading quickly across the world. Many areas in China have also reported scattered cases or clusters of infection, raising the demand for nucleic acid testing significantly.

The way nucleic acid testing is done varies from 1:1 to 5:1 or 10:1 pooled sampling approach – mixing five or 10 samples in one group to speed up testing – and now it's 20:1 to meet the increasing demand.

Compared with nucleic acid testing, antigen testing has advantages like convenience, speediness and low cost, which allows ordinary people to test themselves at home. Antigen testing can help screen out some infected patients quickly and reduce the risk of exposure during nucleic acid testing.

Currently, many countries have their COVID-19 prevention and control strategy based on antigen testing, including those in Europe as well as the United States, Australia, Singapore and Japan.

Q: According to the guideline, residents can buy self-test kits at pharmacies and on e-commerce platforms. Under such condition, do they still need to undergo nucleic acid testing?

Lu: The antigen testing mainly targets patients seeking medical treatment who have a fever, people under quarantine and observation and residents who need to test for the virus by themselves.

It should be noted that due to the limit of the antigen testing's sensitivity, its result cannot be used to prove one's health when seeing a doctor or entering public areas.

Q: How can antigen testing play a better role in the future?

Lu: With the promotion of antigen testing and the updating of its related supporting infrastructure, regions in China can set their own system for people to upload their antigen testing results as medical institutions now do for nucleic acid testing.