BEIJING (Reuters) – China’s coronavirus antibody test, which has made it mandatory for arriving travelers, has raised concerns about its effectiveness after a team of international health experts was denied entry last week after a positive result.
Although the British expert from the World Health Organization (WHO) subsequently tested negative, it is not immediately clear whether the earlier result was false positive or the result of a previous infection or vaccination against COVID-1
Here are details of China’s testing rules, potential policy issues, implications for vaccinated individuals and expert opinions.
WHAT REQUIREMENTS FOR COVID-19 ARE REQUIRED?
Travelers from many countries, such as Canada, Germany, Singapore and the United States, must show negative results for nucleic acid and immunoglobulin M (IgM) tests taken within 48 hours of boarding.
China uses IgM antibodies, which are usually detected at the beginning of infections, as an additional tool to filter out those that may have been infected but get a negative result from nucleic acid tests.
However, some cases show that IgM antibodies can last longer and even after almost complete recovery.
WILL VACCINATED PEOPLE RECEIVE POSITIVE RESULTS FROM THE ANTIBODY?
It is possible, but not always, experts say. Most vaccines target the virus to “jump” to the surface of the virus to elicit an immune response, which may include IgM antibodies.
“We can assume that any vaccine against COVID-19 containing jump protein will induce IgM, and therefore a diagnostic test designed to detect spike-specific IgM will not be able to distinguish vaccination from infection,” said Helen Fletcher, a professor. of Immunology in London School of Hygiene and Tropical Medicine.
Published data on the COVID-19 vaccine from Oxford University / AstraZeneca Plc show that spike protein-induced IgM is detected in some people at least 56 days after immunization, Fletcher said.
IS IT POSSIBLE TO USE DIFFERENT ANTIBODY TESTS?
Tests to detect antibodies triggered by non-jumping proteins may give negative results to those who have received vaccines targeting spiked proteins, said Jin Dong Yang, a professor of virology at the University of Hong Kong.
Spiked-targeted vaccines include those from AstraZeneca, Pfizer Inc and its partner BioNTech and Moderna.
THERE ARE MORE PROBLEMS
However, such tests could be problematic for other types of vaccines, including whole virus-based shots, which several Chinese developers use, some experts say.
“When a person is injected with a whole virus-based inactivated COVID-19 vaccine … there is a high probability that the person will also test positive for protein-free IgM antibodies,” said Ian Jones, a virologist at the British University of Reading.
The Chinese health authority has not clarified whether its test is designed to detect antibodies caused by proteins 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.
In response to a question on the subject, one of the employees of the embassy in Singapore said that a vaccinated foreigner can present an immunization certificate and expect an answer. The Chinese Foreign Ministry declined to comment.
USING A VACCINE OPPORTUNITY PASSPORT?
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 traveling to China much less of a hassle,” said Huang Yangzhong, a health expert at the US Council on Foreign Relations.
“As Western countries achieve herd immunity through mass vaccination, they will begin to open their borders … If China continues to have such stringent testing requirements, its airlines, hospitality and tourism industry will lose.”
The WHO remains cautious: last week it refrained from advising global travel to depend on such evidence, citing “critical uncertainties” about how effectively tests limit the spread as well as their limited availability.
Reporting by Roxanne Liu and; Yew Lun Tian in Beijing; Edited by Miyoung Kim and Clarence Fernandez