Explanator: COVID-19 vaccines add confusion about China’s testing for travelers

BEIJING (Reuters) – A coronavirus antibody test that China made mandatory for incoming travelers sparked concerns about its effectiveness after a member of a team of international health experts was briefly denied entry last week after a positive result .

Although the British specialist at the World Health Organization (WHO) subsequently tested negative, it was not immediately clear whether the previous result was a false positive, or the result of a previous infection or a COVID-19 vaccination.

Here are the details of China’s testing rules, potential problems with the policy, its implications for vaccinated individuals, and expert opinions.

WHAT COVID-19 TESTS ARE NECESSARY?

Travelers from many countries, such as Canada, Germany, Singapore and the United States, are expected to have negative results on nucleic acid and immunoglobulin M (IgM) tests done within 48 hours of departure.

China uses IgM antibodies, normally detected at the beginning of infections, as a complementary tool to filter out those that may have been infected, but obtain a negative result in nucleic acid tests.

However, some cases have shown that IgM antibodies can persist longer, even after an almost complete recovery.

WILL VACCINATED PEOPLE GET POSITIVE ANTIBODY RESULTS?

It is possible, but not always, say experts. Most vaccines target the “peak” protein on the surface of the virus to elicit an immune response that can include IgM antibodies.

“We can assume that any COVID-19 vaccine containing the peak protein will induce IgM and therefore a diagnostic assay designed to detect peak specific IgM will not be able to differentiate vaccination from infection,” said Helen Fletcher, professor of immunology at the London School of Hygiene and Tropical Medicine.

Published data on the Oxford University / AstraZeneca Plc COVID-19 vaccine show that the IgM peak triggered by the protein is detectable in some people at least 56 days after immunization, said Fletcher.

IS IT POSSIBLE TO USE DIFFERENT ANTIBODY TESTS?

Tests to detect antibodies triggered by the non-spike protein may yield negative results for those who received vaccines against the spike protein, said Jin Dong-Yan, professor of virology at the University of Hong Kong.

Vaccines targeting peak protein include those from AstraZeneca, Pfizer Inc and their partner BioNTech and Moderna.

THERE ARE STILL PROBLEMS

These tests, however, can be problematic for other types of vaccines, including whole virus-based vaccines that several Chinese developers use, some experts said.

“When a person is injected with the inactivated COVID-19 vaccine based on whole virus … there is a high chance that the person will also be able to test positive for non-peak IgM antibody tests,” said Ian Jones , virologist at the University of Great Britain to read.

China’s health authority does not say whether the test was developed to detect antibodies triggered by the spike protein or another protein. The National Health Commission did not respond to a request for comment.

CAN VACCINATED PEOPLE ENTER CHINA?

China does not say clearly how it decides to exempt vaccinated people from their requirements for negative antibody tests.

Responding to a question on the matter, one of the staff at the Singapore embassy said that a vaccinated foreigner could present an immunization certificate and wait for an answer. China’s Foreign Ministry declined to comment.

IS USING A VACCINE PASSPORT AN OPTION?

At the G20 summit in November, Chinese President Xi Jinping proposed a global mechanism for the mutual recognition of health certificates, including nucleic acid tests.

Experts hope that China will consider using a vaccine passport to replace the antibody test.

“A vaccine passport will make traveling to China a lot less hassle,” said Huang Yanzhong, a health expert at the United States Council on Foreign Relations.

“As Western countries achieve collective immunity through mass vaccination, they will begin to open their borders … If China continues to have such strict testing requirements, its airlines, hotels and tourism will lose out.”

WHO remains cautious: it abstained last week from advising global travel to be conditioned on such evidence, citing “critical unknowns” about the effectiveness with which tests limit dissemination and also its limited availability.