On 20 July, results from clinical trials of two early-stage COVID-19 vaccines, one developed by University of Oxford and AstraZeneca and another by the Chinese company CanSino Biologics, were reported in the Lancet. Oxford’s simian adenovirus-vectored vaccine (ChAdOx1 nCoV-19) and CanSino’s adenovirus-5-vectored vaccine both elicited neutralizing antibodies and T-cell immune responses to the SARS-CoV-2 virus. (CanSino, based in Tianjin, was the first vaccine developer to publish data from a smaller phase 1 trial, in May.) These publications join Moderna’s mRNA vaccine report from mid-July in the New England Journal of Medicine. Because of different assays used, comparisons among the vaccines are difficult. In broad terms, the two adenovirus-vectored programs gave similar results — upwards of 80–90% of participants marshalled neutralizing antibody and spike-protein-specific T cell responses within 28 days — whereas the Moderna vaccine study reported only neutralizing antibody responses after vaccination. In the single-blind, randomized, placebo-controlled Oxford trial, immune responses lasted the full 56 days of the trial. The researchers inoculated a small cohort of ten people with a second dose of the COVID-19 vaccine after 28 days, which upped the antibody response but not the T-cell one, in keeping with previous observations. Participants in both trials had only mild flu-like symptoms, typically seen with viral-vector-mediated vaccines.
Although the results are promising, both trials involved relative young and ethnically homogenous people; neither of these represent demographics most affected by COVID-19. More diverse populations are included in Cambridge-based AstraZeneca’s phase 3 trials of ChAdOx1 nCoV-19 taking place in South Africa and Brazil. Also on 20 July, Pfizer and German company BioNtech of Mainz published early results in an online preprint server of their mRNA vaccine candidate BNT162b1, showing dose-dependent neutralizing antibody responses and CD4+ and CD8+ T cell responses against the receptor-binding domain of SARS-CoV-2. Ultimately, though, although all of these potential vaccines have shown to engage the immune system, no vaccine developer has yet provided definitive data demonstrating protection from SARS-CoV-2 infection.