Preliminary Step towards COVID-19 Inactivated Vaccine Development in Egypt

The current worldwide COVID-19 pandemic is causing severe human health problems, with high mortality rates and huge economic burdens requiring the urgent development of a safe and effective vaccine. Here, preclinical evaluation of an inactivated SARS-CoV-2 vaccine candidate (EgySerVac-20) is reported. Oropharyngeal swabs and nasopharyngeal aspirates obtained from Egyptian patients with laboratory-confirmed SARS-CoV-2 infection were isolated using Vero cells and were then genetically characterized. Vaccine inactivation was performed using diluted formaldehyde, followed by safety testing for the inactivated vaccine. To determine the high humoral immune responses against SARSCOV-2 infection, the safety and capacity of the vaccine prepared with alum adjuvant were tested. The immunogenicity and efficacy of the vaccine candidate was tested in vitro by a neutralization assay and in vivo using mouse models. Our results revealed a cytopathic effect which was observed 48 hours post infection and the viral particles were identified by rRT-PCR as SARS-CoV-2. Propagation of the isolated virus in ten serial passages on the Vero cells yielded a virus titer 7.5 log10 TCID50/ml. Complete inactivation of SARS-CoV-2 was observed at 37°C in 24 hours post treatment by diluted formaldehyde. Inactivated SARS-CoV-2 infected fluid safety was determined by absence of cytopathic effect by repeated passage in Vero cell line, indicating loss of virus infectivity. Virus inactivated by diluted formaldehyde showed no deaths or clinical symptoms in mice groups post intraperitoneal inoculation (0.5ml/mouse). EgySerVac-20 inactivated vaccine has safely induced high levels of neutralizing antibodies titers in mice, where 0.1 ml immunization dose showed protective efficacy against SARS-CoV-2 challenge in mice. This finding will support the future preclinical and clinical trials evaluation for our SARS-CoV-2 vaccine candidate in primates and human, respectively.