Since the emergence of the severe acute respiratory syndrome coronavirus 2019 (COVID-19) pandemic 2 (SARS-CoV-2), scientists and policy makers have continued to work relentlessly to control the epidemic. The availability of multiple COVID-19 vaccines, developed on different platforms, is a powerful tool in containing the epidemic.
Previous studies have reported the efficacy of COVID-19 vaccines, developed on different platforms, such as messenger RNA (mRNA) and recombinant helper protein. These vaccines have shown efficacy rates between 90 and 96% in avoiding severe COVID-19 against the original SARS-CoV-2 strain.
Several new variants of SARS-CoV-2 emerged due to genetic mutations, which were classified as variants of concern (VOC) and variants of interest (VOI) based on their transmissibility, virulence, and ability to evade immune protection.
The SARS-CoV-2 Delta variants and Omicron have been classified as VOCs due to their high transmissibility. These variants spread prevalently in most countries around the world and increased the incidence of infection. The increasing rate of superinfection indicates a reduced efficacy of available COVID-19 vaccines against novel SARS-CoV-2 variants.
Scientists have developed a protein subunit-based COVID-19 vaccine known as ZF2001, which targets the tandem-duplicate receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. They produced antigen protein in Chinese hamster ovary cells and treated it with aluminum hydroxide (an adjuvant) to develop the vaccine. One of the main advantages of this vaccine is that it does not require harsh cold conditions for storage and transportation.
Study: Efficacy and safety of the RBD-Dimer-ZF2001-based Covid-19 vaccine in adults. Image Credit: LookerStudio / Shutterstock
Initial preclinical studies of the ZF2001 vaccine using rodents and macaques revealed promising efficacy against SARS-CoV-2. In addition, Phase 1 and 2 clinical trials have also reported that the vaccine is safe and effective in humans. The scientists designed a three-dose regimen in a phase 3 trial of ZF2001.
A new study was published in New England Journal of Medicine Discuss the efficacy and safety profile of the ZF2001 vaccine in adults, based on a randomized, placebo-controlled, multinational, double-blind Phase III trial. During this study, the SARS-CoV-2 Delta variant was highly prevalent globally.
This trial was conducted in thirty-one clinical centers across Indonesia, Ecuador, Uzbekistan and Pakistan. Another center was set up in China to determine the safety profile for ZF2001 only. In this phase 3 trial, all participants were 18 years of age or older and were vaccinated with three doses of 25 mcg of ZF2001 or a placebo, thirty days apart. Vaccine efficacy was estimated at least seven days after the third dose of vaccine was administered and follow-up was conducted for six months.
The scientists designed the current experiment as a case study. In this study, 28,873 participants were given at least one dose of ZF2001 or a placebo between December 12, 2020 and December 15, 2021, and a safety analysis was considered. The researchers determined the effectiveness of the vaccine by analyzing 25,193 participants who received three doses of the vaccine.
Scientists reported that severe and critical SARS-CoV-2 infection occurred in six participants vaccinated with ZF2001 and forty-three participants receiving a placebo. The estimated efficacy of the vaccine against severe COVID-19 was 92.9% at short-term follow-up and 87.6% at long-term follow-up. In addition, two cases of COVID-19-related deaths were reported among those vaccinated with ZF2001 and twelve participants who received a placebo. Importantly, no vaccine-related deaths occurred, and most adverse reactions were found to be around grade I or II.
Scientists analyzed the short- and long-term effectiveness of the vaccine. They reported the short-term efficacy of three doses of ZF2001 to be 81.4% and the long-term efficacy 75.7%. The authors stated that this vaccine not only met, but significantly exceeded, pre-established success criteria.
The present study indicated that ZF2001 confers a high level of protection against different variants of SARS-CoV-2. The vaccine was found to be highly effective against the Alpha, Kappa and Delta variants. Importantly, this study established a safety and reactivity profile for ZF2001, which was found to be comparable to Phase 1 and 2 reports. The authors also stated that in this Phase 3 trial, older participants, over 60 years of age, and demonstrating major events were included. Less passive and reactive compared to younger participants. The results strongly support the efficacy of the ZF2001 vaccine against SARS-CoV-2.
The authors noted some limitations associated with the current study. First, the study group mostly included Asian participants, that is, 78.5%; However, the ideal group should include a diverse population. In addition, the number of older participants over 60 years of age was limited in the study group. Hence, in the future, the efficacy of the vaccine for this group should be evaluated in real-world conditions. The current study did not assess the vaccine’s efficacy against asymptomatic COVID-19 infection, which future research could take into account.