Abstract
In March 2020, the first cases of the human coronavirus disease COVID-19 were registered in Kazakhstan. We isolated the SARS-CoV-2 virus from clinical materials from some of these patients. Subsequently, a whole virion inactivated candidate vaccine, QazCovid-in, was developed based on this virus. To develop the vaccine, a virus grown in Vero cell culture was used, which was inactivated with formaldehyde, purified, concentrated, sterilized by filtration, and then adsorbed on aluminum hydroxide gel particles. The formula virus and adjuvant in buffer saline solution were used as the vaccine. The safety and protective effectiveness of the developed vaccine were studied in Syrian hamsters. The results of the studies showed the absolute safety of the candidate vaccine in the Syrian hamsters. When studying the protective effectiveness, the developed vaccine with an immunizing dose of 5 μg/dose specific antigen protected animals from a wild homologous virus at a dose of 104.5 TCID50/mL. The candidate vaccine induced the formation of virus-neutralizing antibodies in vaccinated hamsters at titers of 3.3 ± 1.45 log2 to 7.25 ± 0.78 log2, and these antibodies were retained for 6 months (observation period) for the indicated titers. No viral replication was detected in vaccinated hamsters, protected against the development of acute pneumonia, and ensured 100% survival of the animals. Further, no replicative virus was isolated from the lungs of vaccinated animals. However, a virulent virus was isolated from the lungs of unvaccinated animals at relatively high titers, reaching 4.5 ± 0.7 log TCID50/mL. After challenge infection, 100% of unvaccinated hamsters showed clinical symptoms (stress state, passivity, tousled coat, decreased body temperature, and body weight, and the development of acute pneumonia), with 25 ± 5% dying. These findings pave the way for testing the candidate vaccine in clinical human trials.
Highlights
MATERIALS AND METHODSCoronaviruses (CoV) are a large family of RNA-containing viruses that can infect humans and certain animal species (Weiss and Navas-Martin, 2005; To et al, 2013; Lau and Chan, 2015)
We present the results of the creation of a new inactivated candidate vaccine QazCovid-in and the study of its safety and immunological effectiveness in Syrian hamsters
In Kazakhstan, research into developing a vaccine against the new coronavirus infection begun within the framework of a state-sponsored special scientific and technical program when the first cases of the disease were detected in the country in March 2020
Summary
Coronaviruses (CoV) are a large family of RNA-containing viruses that can infect humans and certain animal species (Weiss and Navas-Martin, 2005; To et al, 2013; Lau and Chan, 2015). To prepare the vaccine and to infect hamsters, we used the 4th passage of the virus grown in a Vero cell culture at a titer of 7.25 ± 0.25 log TCID50/mL. Blood samples were taken from the animals before vaccination for the determination of virus neutralizing antibodies (VNA) to FIGURE 2 | Study design of QazCovid-in vaccination in Syrian hamsters. To establish the protective efficacy of the vaccine, the infectious process was modeled on vaccinated and control (unvaccinated) Syrian hamsters by injecting them with the wild homologous SARS-CoV-2 virus at a dose of 104.5 TCID50/animal in a volume of 100 μL intranasally. The virus was isolated from lung samples in which viral RNA was detected by PCR For this purpose, a 20% organ-tissue suspension was prepared from the lungs of hamsters using a generally accepted technique. PV was evaluated by the Kaplan-Meyer method, and PV indicators in the groups of vaccinated and unvaccinated animals were compared by the log-rank method. p < 0.05 was considered statistically significant
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