A pre-print paper describes a chimpanzee adenovirus-vectored vaccine that, when administered intranasally in rhesus macaques, led to a robust immune response and demonstrated protection against infection by the virus that causes COVID-19. This vaccine is a chimpanzee Adenovirus (simian Ad-36)-based SARS-CoV-2 vaccine (ChAd-SARS-CoV-2-S) that expresses the S protein.
Post-vaccination, the researchers found anti-S, anti-RBD, and neutralizing antibodies. T cell responses were also present. In nasal swabs, viral RNA loads were lowered in immunized animals, and only one had a detectable infectious virus on day one post-challenge, compared to four of six controls. The researchers also measured the infection level in bronchoalveolar lavage fluid (BALF) on day 1 and 3 post-challenge and lung tissues (day 7), from exposed animals. One of six samples on day 1 were positive for infectious virus, vs all control samples.
The viral titer was also less by three orders of magnitude. On day 3, only one sample from a control animal was positive for infectious virus. Viral RNA was increased a hundred-fold and fifty-fold, on day 1 and 3, respectively, in control BALF samples relative to immunized animals, supporting viral clearance. A single dose of this vaccine significantly reduced the incidence of disease and viral spread of SARS-CoV-2. The absence of vaccine-dependent enhancement of disease is another encouraging sign. However, further research is required to compare the immunity achieved with intranasal and IM administration of this vaccine.
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