The Omicron coronavirus variant is likely to enter China, but mainstream tests will be able to detect any cases, and the country’s zero-Covid response will block community transmission, according to a senior public health official.
“Omicron was present not only in Africa but also [many countries outside Africa] and might possibly have spread in the community, which means the variant has a high chance of being introduced to China,” Xu Wenbo, head of the National Institute for Viral Disease Control and Prevention under the China CDC, told state broadcaster China Central Television on Monday night.
But, because of the design of China’s coronavirus tests, the variant would be detected, he said.
Tests on swabs of saliva or nasal samples look for specific markers in the genetic material to identify the presence of the coronavirus as an indicator of infection. Usually, two or more such markers are searched to ensure the match is correct.
Tests designed to recognise markers in the spike protein, which plays a key role in allowing the virus to enter human cells, may report a false negative because the Omicron variant features a large number of mutations on the spike that tests may not recognise as the virus being tested.
Over the weekend, the World Health Organization said one of the widely used tests that could not detect the S gene of the virus – referred to as S gene drop-out or target failure – could be used as an indicator of Omicron infection, but it needed to be confirmed with genome sequencing.
Xu said the mainstream tests in China were based on a design by the Chinese Centre for Disease Control and
Prevention that targeted the open reading frame (ORF) group of genes and the N gene, and therefore the sensitivity and specificity of the tests would not be affected by the Omicron variant.
The Omicron variant, assessed by the WHO as posing a “very high” global risk, has been seen as a big threat in the pandemic with some of the mutations to the spike protein being seen in other more transmissible or pathogenic variants.
The National Health Commission said on Monday night that the Chinese CDC had developed a specific test for the Omicron variant and was carrying out genomic surveillance of the virus to detect potential imported cases. It said these measures would aid “timely detection” of Omicron cases.
Researchers are still studying whether the variant is more transmissible and if it is more likely to escape the protection of vaccines or past infections, but countries have moved quickly to impose travel restrictions and stricter public health measures as a precaution.
Xu said more mutation sites on the virus did not necessarily translate to higher transmissibility or stronger immune escape than the Delta variant because “aggregated mutations are not necessarily a cumulative form of mutations”.
“Structural virology, cross-immune neutralisation and field epidemiology are also needed to see the protection of the vaccine. Overall, the mutant strain and the serotype are still of the Sars-CoV-2 [the virus that causes Covid-19], so there will not be disruptive change,” Xu said.
He said the existing response to Covid-19 – preventing community spread with detailed epidemiological investigation and genetic surveillance of all imported cases – was capable of stopping the spread of the Omicron variant.
China’s prevention and control efforts would be routine, with increased self-monitoring and testing for some high-risk jobs, Xu said, adding that precautions should be stricter for jobs requiring contact with countries with outbreaks, or for isolated hotels and airports associated with imported cases.
More than 30 local outbreaks that occurred in China after April 2020 – when China halted local transmission of the initial Covid-19 outbreaks across the country – were linked to imported cases or cold-chain products.
The country eventually relied on “dynamic zero Covid” response to interrupt transmission, Xu said, referring to China’s strategy of cutting off community transmission as soon as possible with travel restrictions, lockdown, rigorous testing, isolation and other measures.
The NHC advised residents to continue wearing masks indoors and on transport even if they had been fully vaccinated or administered the booster dose because masking remained the most effective measure to block virus transmission.
The NHC also asked residents to cease overseas travel unless “absolutely necessary”.