Two More COVID-19 Candidate Vaccines Show Promise

By Amy Orciari Herman

Edited by Susan Sadoughi, MD, and André Sofair, MD, MPH

Two experimental vaccines against SARS-CoV-2 show promise in early, industry-supported trials published in The Lancet.

In a U.K.-based phase 1/2 trial, nearly 1100 adults without a history of SARS-CoV-2 infection were randomized to receive either a chimpanzee adenovirus-vectored vaccine expressing the SARS-CoV-2 spike protein (ChAdOx1 nCoV-19) or a meningococcal conjugate vaccine as a control. With one dose of ChAdOx1 nCoV-19, antibodies to SARS-CoV-2 peaked by day 28 and remained high through day 56. Ten participants who received a booster dose on day 28 achieved higher antibody levels. In addition, neutralizing antibodies against SARS-CoV-2 were detected in over 90% of participants tested. ChAdOx1 nCoV-19 caused more local and systemic reactions (e.g., chills, fever) than did the control vaccine, but these were lessened with prophylactic acetaminophen.

Next, in a phase 2 trial conducted in China, roughly 500 healthy adults were randomized to receive one injection of a non-replicating adenovirus type-5-vectored COVID-19 vaccine (at 1 of 2 concentrations) or a placebo. With the COVID-19 vaccine, antibody responses were noted beginning on day 14, and nearly all participants had seroconverted by day 28. Additionally, both vaccine doses achieved significant neutralizing antibody responses. The most common systemic reactions — fatigue, fever, and headache — occurred more often with the COVID-19 vaccine than with placebo.

Commentators say the results "augur well for phase 3 trials, where the vaccines must be tested on much larger populations of participants to assess their efficacy and safety."