Here, we showed that a single vaccination with ChAdOx1 nCoV-19 is effective in preventing damage to the lungs upon high dose challenge with SARS-CoV-2. Similarly a recent study showed that a triple vaccination regime of a high dose of whole inactivated SARS-CoV-2 protected rhesus macaques from SARS-CoV-2 pneumonia
7.
Viral loads in BAL fluid and lung tissue of vaccinated animals were significantly reduced, suggesting that vaccination prevents virus replication in the lower respiratory tract. Despite this marked difference in virus replication in the lungs, reduction in viral shedding from the nose was not observed. However, animals were challenged with a high dose of virus via multiple routes, which likely does not reflect a realistic human exposure. Whether a lower challenge dose would result in more efficient protection of the upper respiratory tract remains to be determined.
Several preclinical studies of vaccines against SARS-CoV-1 resulted in immunopathology after vaccination and challenge, with more severe disease in vaccinated animals than in controls
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10. Importantly, we did not see any evidence of immune-enhanced disease in vaccinated animals. The immune response was not skewed towards a Th2 response in mice nor in NHPs, there was no increase in clinical signs or virus replication throughout the study in vaccinated NHPs compared to controls and no markers of disease enhancement in lung tissue of NHPs, such as an influx of neutrophils were observed. These data informed the start of the phase I clinical trial with ChAdOx1 nCoV-19 on April 23, 2020. As of May 13, 2020, more than 1000 volunteers have participated in the clinical trials. This study is thus an important step towards the development of a safe and efficacious SARS-CoV-2 vaccine.