Expert says containment measures key to stemming spread of delta variant

China's containment measures against COVID-19 infections are essential to stem the spread of the highly contagious delta variant of the novel coronavirus, and its domestic vaccines have proved effective against the new strain, a prominent Chinese respiratory expert said recently.

The country reported no new confirmed local infections on Sunday, the first time since late July when a series of local outbreaks driven by the delta variant broke out and later spread to 18 provincial-level regions, according to the National Health Commission.

Zhong Nanshan, a top infectious disease and respiratory expert based in Guangzhou, Guangdong province, said during an event on Friday that the delta strain is capable of causing a surge in infections due to its heightened transmissibility.

"As a result, the top priority at present is to cut off its transmission chain, which should be a guiding principle for our disease-control work," he said.

The World Health Organization has divided the global pandemic response into four categories, from aggressive containment and suppression, to mitigation and no substantive strategy.

Zhong said China's assertive control of the virus' spread has yielded positive results and provided valuable experiences for future battles against the disease.

As the country's mass COVID-19 vaccination program is progressing smoothly, he said that given an average efficacy rate of 70 percent for domestic vaccines, at least 80 percent of China's population should be fully vaccinated to establish herd immunity against the virus.

The threshold will likely be reached by the end of this year, he added. The commission said on Monday that China had administered nearly 1.95 billion COVID-19 doses as of Sunday.

Zhong said a real-world study conducted by disease-control workers in Guangdong province shows that domestic inactivated vaccines have an overall effectiveness rate of nearly 60 percent against the delta variant. They are also 70 percent effective against moderate infections and 100 percent effective at preventing severe illnesses.

The study was published in the journal Emerging Microbes& Infections on Aug 14.

In a commentary on the study, researchers from the Chinese Center for Disease Control and Prevention said its findings helped build confidence in expanding the domestic vaccination campaign to cover children and teenagers.

As two domestic inactivated vaccines have obtained emergency use approval from the WHO and are being distributed widely in developing countries, the commentary said the new study also provides assurance to the international community that Chinese vaccines can tackle the highly transmissible variant.

The commentary was published on China CDC Weekly, an academic platform established by China CDC, on Friday.

However, Zhong noted that vaccine-induced protection tends to dwindle about six months after full inoculation. The phenomenon has been observed in different types of vaccines, including the mRNA vaccine developed by German biotechnology company BioNTech with the assistance of Pfizer in the United States.

Delivering a booster shot is a promising approach to cope with diminished effectiveness, he said, adding that domestic and foreign vaccine developers are stepping up research into booster shots.

Zhong said the latest research shows that an additional dose of domestic inactivated vaccine can increase antibody levels by over 10 times.

China has granted conditional market approval or emergency use authorization for nine domestically developed vaccines.