BEIJING (Reuters) – A coronavirus antibody test that China has made mandatory for arriving travelers has raised concerns about its effectiveness after one of a team of international health experts was briefly denied entry last week after a positive result.
Although the British World Health Organization (WHO) expert 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 details of China’s testing rules, potential policy issues, implications for vaccinated individuals, and expert opinion.
WHICH COVID-19 TESTS ARE REQUIRED?
Travelers from many countries, such as Canada, Germany, Singapore, and the United States, must show negative results of nucleic acid and immunoglobulin M (IgM) antibody tests within 48 hours of boarding.
China is using IgM antibodies, which are normally detected early in infections, as an additional tool to filter out those who may be infected but get a negative result in nucleic acid tests.
In some cases, however, it has been shown that IgM antibodies can last longer, and even after almost complete recovery.
WILL VACCINATED PEOPLE GET POSITIVE ANTIBODY RESULTS?
It’s possible, but not always, experts say. Most vaccines target the “spike” protein on the virus surface to trigger an immune response that may include IgM antibodies.
“We can assume that any COVID-19 vaccine containing the spike 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 at London University. School of Hygiene & Tropical Medicine.
Published data on the COVID-19 vaccine from Oxford University / AstraZeneca Plc shows that peak protein-triggered IgM is detectable in some people at least 56 days after immunization, Fletcher said.
IS IT POSSIBLE TO USE DIFFERENT ANTIBODY TESTS?
Tests to detect antibodies activated by non-spike protein may yield negative results for those who have received vaccines targeting spike protein, said Jin Dong-Yan, a professor of virology at the University of Hong Kong.
Vaccines targeting spike protein 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 shots used by different Chinese developers, some experts said.
“If a person is injected with a completely virus-based, inactivated COVID-19 vaccine … there is a good chance that the person will also have a positive result on IgM antibody tests for non-spike protein,” says Ian Jones, a virologist at the British University of Reading.
The Chinese health authority is not clear whether its test is designed to detect antibodies activated by spike protein or other protein. The National Health Commission did not respond to a request for comment.
CAN VACCINATED PEOPLE ENTER CHINA?
China is unclear about how the decision to exempt vaccinated people from the requirements for negative antibody tests.
In response to a question on the subject, one of the staff at the Embassy in Singapore said that a vaccinated foreigner can provide an immunization certificate and wait for a response. China’s Foreign Ministry declined to comment.
IS THE USE OF 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 testing.
Experts hope China will consider using a vaccine passport to replace the antibody test.
“A vaccine passport will make travel to China much less hassle,” said Huang Yanzhong, a health expert with the US think tank Council on Foreign Relations.
“As Western countries gain immunity to herds through mass vaccination, they will begin to open their borders … If China continues to have such a strict testing requirement, the aviation, hotel and tourism industries will lose out.”
The WHO remains cautious: last week refrained from advising that travel around the world should depend on such evidence, citing “critical unknowns” about how effectively the tests limit dissemination and also their limited availability.
Reporting by Roxanne Liu and; Yew Lun Tian in Beijing; Edited by Miyoung Kim and Clarence Fernandez