Explanator: COVID-19 vaccines increase confusion over China’s travel tests

BEIJING (Reuters) – An antibody test against coronavirus that China has made mandatory for arriving travelers has raised concerns about its effectiveness after it was briefly denied entry by a team of international health experts last week , after a positive result.

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

Here are details about China’s testing rules, potential policy issues, its implications for vaccinated people and expert opinions.

WHAT COVID-19 TESTS ARE NECESSARY?

Travelers from many countries, such as Canada, Germany, Singapore and the United States, must test negative for nucleic acid and immunoglobulin M (IgM) antibodies tested within 48 hours of boarding.

China uses IgM antibodies, normally detected at the beginning of infections, as an additional tool to filter out those who may have been infected, but get a negative result on nucleic acid tests.

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

WILL VACCINATED PEOPLE GET POSITIVE ANTIBODY RESULTS?

It is possible, but not always, experts say. Most vaccines target the spike protein on the surface of the virus to trigger an immune response that could include IgM antibodies.

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

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

IS IT POSSIBLE TO USE DIFFERENT ANTIBODY TESTS?

Tests for antibodies to non-spike proteins can produce negative results for those who have received spike protein vaccines, said Jin Dong-Yan, a professor of virology at the University of Hong Kong.

Spike protein vaccines include those from AstraZeneca, Pfizer Inc. and its partner BioNTech and Moderna.

THERE ARE STILL PROBLEMS

However, such tests can be problematic for other types of vaccines, including whole virus-based photos used by several Chinese developers, some experts said.

“If a person is injected with a whole virus inactivated COVID-19 vaccine … there is a strong chance that the person will also test positive for non-spike IgM protein antibodies.” said Ian Jones, a virologist at the University of UK Reading.

The Chinese health authority does not clarify whether its test is designed to detect antibodies triggered by spike protein or other proteins. 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 its requirements for negative antibody tests.

Answering a question on the subject, one of the employees of his embassy in Singapore said that a vaccinated foreigner can submit an immunization certificate and can 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 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 the trip to China much less difficult,” said Huang Yanzhong, a health expert at the US Foreign Relations Council’s think tank.

“As Western countries gain immunity from mass vaccination, they will begin to open their borders … If China continues to have such a strict testing requirement, its airlines, hotels and tourism companies will lose.” .

The WHO remains cautious: it refrained last week from recommending that global travel be conditioned by such evidence, citing “unknown critics” about how effectively tests limit their spread and also their limited availability.