Anexperimental Covid-19 vaccine developed by researchers at the University of Oxford in the U.K. triggered an immune response in healthy adults and appears to have no dangerous side effects, according to research published Monday in the scientific journal The Lancet.
The study included 1,077 healthy people aged 18 to 55, about half of whom received the experimental Covid-19 vaccine. Ten of those people received two doses. The other half, a control group, received a meningitis vaccine that’s already on the market.
The Covid-19 vaccine seemed to spur an immune response, and in 32 out of 35 people, investigators found evidence of so-called “neutralizing” antibodies. These special antibodies are believed to be protective against the SARS-CoV-2 virus. They were still detectable about two months after one dose of the vaccine. Antibody levels were even higher in the ten participants who received a booster shot 28 days after the first one. It’s not known how long these antibodies will stick around in the blood or whether they can effectively block infection.
We don’t know yet how many of the other 508 people who received the coronavirus vaccine made neutralizing antibodies. The researchers reported on just a small group that had been tested for them. Confirming the presence of neutralizing antibodies is slower and more difficult than conducting other antibody tests, so it’s possible that researchers have not yet tested everyone in the trial.
“There is still much work to be done before we can confirm if our vaccine will help manage the Covid-19 pandemic,” co-author Sarah Gilbert, PhD, a professor of virology at the University of Oxford, said in a statement. “We still do not know how strong an immune response we need to provoke to effectively protect against SARS-CoV-2 infection.”
The vaccine also prompted another kind of immune response, involving T cells — white blood cells that might be also important in Covid-19 immunity. These specialized immune cells are capable of seeking out and destroying cells infected with SARS-CoV-2. Experts say that a combination of T cells and neutralizing antibodies might be needed for protection against the virus.
A small number of people in the trial had detectable neutralizing antibodies and T cell responses against SARS-CoV-2 spike before they received the experimental vaccine, which is likely indicative of a past asymptomatic infection. People with previous or current Covid-19 symptoms and those who have tested positive for the virus aren’t eligible for the study.
While muscle ache, fatigue, chills, and feeling feverish were commonly reported side effects, there were no life-threatening adverse effects that required hospitalization. In those who received the coronavirus vaccine, 56 were also asked to take an over-the-counter painkiller, which helped reduce reactions to the vaccine. The authors say they will now follow participants for at least one year to monitor the vaccine’s safety and the immune response it provokes.
In the current trial, 91% of participants are white and the average age is 35 years. It’s not yet known whether a Covid-19 vaccine will work as well in the elderly, who tend to mount weaker immune responses to vaccines.
Oxford’s vaccine uses a genetically modified chimpanzee virus that codes for the signature “spike” protein found on the surface of the SARS-CoV-2 virus. No vaccines that use this technology are available for widespread use, but the approach has been tested in experimental vaccines for Ebola, Zika, and Middle East respiratory syndrome (MERS), another coronavirus.
This technology is different from other front-runner coronavirus vaccines, like the one developed by Massachusetts biotech company Moderna and the U.S. National Institutes of Health, which is an RNA vaccine.
By the fall, researchers could get a first glimpse at how effective these vaccines area. Moderna says it plan to launch a larger trial — known as a Phase 3 study—of 30,000 people by the end of July.
Meanwhile, Oxford and its pharma partner AstraZeneca just began a large Phase 3 trial. This phase is recruiting 10,000 trial participants in the U.K., about 5,000 in Brazil, and 2,000 in South Africa. A second trial in the United States aims to enroll as many as 30,000 participants.
According to a July 16 report in the Guardian, the Oxford researchers are also planning a so-called challenge trial, in which healthy young participants will be vaccinated then deliberately infected with SARS-CoV-2. These kinds of experiments can quickly reveal how effective a vaccine is, but they’re controversial for Covid-19 since a person could get very sick and effective treatments aren’t available yet.
AstraZeneca has committed to producing 2 billion doses if the Oxford vaccine is found to be effective and gets a greenlight from regulators. But developing a Covid-19 vaccine that works is just the first step and its success will hinge on how it’s rolled out to the public. Manufacturing and delivering a vaccine to everyone who needs one will take a massive coordinated effort on a scale that hasn’t been seen before.