Early results from separate British and Chinese candidate coronavirus vaccines reported on Monday showed promising signs of immunity and no serious side effects.
The early results from 1,077 volunteers in an Oxford University study and 508 adults in the CanSino Biologics study conducted in Wuhan, China, are encouraging as both studies move to widespread testing of the vaccines in tens of thousands of volunteers, said experts.
"Overall, the results of both trials are broadly similar and promising," wrote Johns Hopkins Bloomberg School of Public Health vaccine experts Naor Bar-Zeev and William Moss, in a commentary accompanying the studies. "The safety signals from these two important trials are reassuring."
The monthlong trials in healthy volunteers both produced "neutralizing" antibodies — in 90% of the Oxford participants and 85% of the Wuhan ones — seen as a marker of an effective vaccine. They also led to development of longer-lived T cells responding to the inoculations, a marker of a long-term immune system response to a virus.
"Both the Oxford and Beijing vaccines induce a high-frequency, antiviral, T cell response, which looks promising," Imperial College professor of medicine Daniel Altmann told BuzzFeed News.
Both vaccines rely on harmless viruses engineered to contain parts of spike proteins from SARS-CoV-2 to trigger an immune response after injection, a new approach to vaccination developed against influenza and Ebola in the last decade. The Oxford University vaccine is being developed with AstraZeneca, part of the Operation Warp Speed candidates, supported by more than $1 billion from the US Biomedical Advanced Research and Development Authority.
Tolerable fatigue, headache, and arm tenderness were the only side effects reported by the volunteers, similar to other vaccines, according to the studies. In the Oxford trial, some participants were given a second booster shot, spurring the production of antibodies without any side effects or signs of a feared excessive immune response. The CanSino trial tested both a low dose and moderate dose inoculation, resulting in very similar immune responses, after an earlier small trial showed more side effects from high doses.
Less than a year into a global pandemic, key unanswered questions about a vaccine for the novel coronavirus remain, including to what extent the candidates will prevent people from getting infected or transmitting the virus, rather than merely limiting the severity of an infection. Another question is whether vaccinations will be required every year.
Right now, three candidate coronavirus vaccines are in the final Phase 3 stage of testing on tens of thousands of volunteers, according to the World Health Organization. Those three are the University of Oxford candidate, one from a Chinese pharmaceutical company called Sinovac, and one from Moderna in the US. The Sinovac candidate is an inoculation with dead virus particles used in vaccines for decades, while the Moderna one is a cutting-edge "RNA vaccine" that sends genes for virus antigens that prime the immune system to ward off an infection.
The Phase 3 candidates from Oxford and Siniovac have already started recruiting volunteers for the trials, while Moderna is expected to start before the end of July. Experts hope that by the end of the year these trials will determine whether the vaccine candidates are safe and effective enough for widespread inoculation of millions of people.