BEIJING (Xinhua) -- A new study said that in the absence of vaccines for the Omicron mutant , extending the vaccination period between doses may contribute to halting the rapid emergence of this sub-mutant of COVID-19.

The study, published in The New England Journal of Medicine earlier this month, was led by Gao Fu, academician of the Chinese Academy of Sciences (CAS), head of the Chinese Center for Disease Control and Prevention.

In the study, the researchers evaluated levels of neutralization against the original SARS-CoV-2 and sub-variants of Omicron including BA.4 and BA.5 in blood samples collected from people who had received three doses of Chinese inactivated vaccines, three doses of a ZF2001 protein subunit vaccine. , or two doses of inactivated vaccines boosted by ZF2001.

The results showed that in each vaccine group, levels of neutralizing antibodies against all Omicron sub-variants tested were significantly lower than levels against the original strain of the virus, indicating that said sub-variants have the ability to evade immune protection.

But for ZF2001, the researchers found that levels of neutralizing antibodies rose as the interval between the second and third doses increased, particularly against sub-Omicron variants.

For vaccine recipients who had a four- to six-month interval between the second and third doses, their neutralizing antibody levels were approximately a factor 10 higher against the original variant and about 30 higher against all of the Omicron sub-variants, compared to those with a one-month interval between doses.

The authors explain that the better performance of ZF2001 is due to its use of its receptor-binding domain as an antigen, which can induce increased levels of neutralizing antibodies against sub-Omicron variants by administering multiple booster doses.

ZF2001 was jointly developed by the Institute of Microbiology under CAS, and Anhui Qifei Longcome Biopharmaceutical Co., Ltd. China granted conditional market approval for the vaccine in March.

The sub-Omicron variant has become a dominant strain of COVID-19 worldwide, causing cluster infections in China, where regions including Beijing, Tianjin and Shaanxi have recently reported locally transmitted COVID-19 cases of the Omicron variant arriving from abroad.

According to the study, in order to better protect against immune evasion of current and potential future pandemic variants, there is still a need to develop updated vaccines as boosters.