China: Zhefei's 3-dose COVID vaccine effective against Delta variant finds new study

In a boost to China's vaccination program, a new study has found that Zhefei's COVID vaccine (ZF2001) is effective against the rapidly spreading Delta variant of the Coronavirus (COVID-19). The study titled 'Neutralization of recombinant RBD-subunit vaccine ZF2001-elicited antisera to SARS-CoV-2 variants including Delta' uploaded to the pre-print medical server 'Biorxiv' on Saturday, claims that the vaccine was effective against all four variants of concern (Alpha, Beta, Gamma and Delta) and other three variants of interest (Epsilon, Eta and Kappa). This vaccine is currently undergoing phase-3 trials and has been given emergency authorisation in China and Uzbekistan.

Zhefei vaccine effective against Delta variant

As per the study, samples from 28 candidates (13 males and 15 females) who received all three vaccine doses of ZF2001 were studied for all seven variants. ZF2001's response against the Epsilon (B.1.429) and Delta (B.1.617.2) was roughly equivalent to its response to the Alpha variant. The study found that volunteers with an extended interval between the second and third doses showed higher neutralisation activity to variants than those with shorter intervals. 

The study analyzed the reactions of two set of subjects - (1) who were administered the 2nd and 3rd dose at 1 week and 2 weeks after the first dose and (2) who were administered the 2nd and 3rd dose at 1 week and 4-6 weeks after the first dose. It was found that the first set of subjects showed a poorer response to six of the seven variants except the Alpha variant. On the other hand, the second set of subjects showed reduced response only to the double mutation variant (Kappa) - a subset of the Delta variant.

"The better performance of the 0-1-(4-6) regimen is likely due to the benefit from the prolonged antibody maturation in individuals," concluded the study. It added, "The high susceptibility of these newly emerged variants to ZF2001 vaccine supports the current mass immunization to build a herd immunity. However, the vaccine effectiveness against these variants must be validated by phase 3 clinical trials and real-world evidences".

About ZF001

The Chinese vaccine by Zhefei (ZF001) is a protein subunit vaccine, currently in phase 3 clinical trials, using tandem repeat SARS-CoV-2 spike receptor-binding domain (RBD) dimer as the antigen. ZF2001 has received emergency use authorization (EUA) in both China and Uzbekistan since March 2021. It has been approved for vaccination with a three-dose regimen.