One of the leading coronavirus vaccine candidates shows promise in early trials, triggering participants to build up immune cells against the virus without causing any severe reactions, according to results published today.
The vaccine, called ChAdOx1 nCoV-19 and being developed by Oxford University in the United Kingdom, is made up of a weakened version of a common cold virus called an adenovirus that infects chimpanzees, Live Science previously reported. The team genetically altered the virus so that it couldn't replicate and grow in humans, and they added genes that code for the so-called "spike" proteins that the coronavirus uses to infect human cells, according to the new study. The idea is that the vaccine will teach human immune cells to recognize the spike protein, so that if a person gets exposed to the coronavirus, their immune system can destroy it.
The Oxford team began testing the vaccine on people in April and published early results from their phase 1 and still-ongoing phase 2 trials today (July 20) in the journal The Lancet. In these two early phases, researchers tested the safety and immune response of a vaccine on a total of 1,077 participants between the ages of 18 and 55 who had no history of COVID-19 across five U.K. hospitals.
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Half of the participants received the candidate vaccine and half, a control vaccine that targets meningococcal bacteria. The meningococcal vaccine served as the control so that participants wouldn't be able to guess whether they received the actual vaccine or the control, because both might cause similar side effects. Participants had blood samples drawn on the day they were given the vaccine and 28 days later; they will also be followed up 184 days and 364 days after first receiving the vaccine, according to the study. Safety and immune response was evaluated in all participants who received ChAdOx1 nCoV-19, but some had additional blood drawn to measure their immune response in more detail. A small subset of the participants also received a second dose of the vaccine.
The researchers found that the vaccine didn't cause any serious adverse events, but it did prompt some mild side effects, including fatigue, fever, headache, pain at the injection site, muscle ache and chills. A subset of participants were asked to take paracetamol (a brand of acetaminophen, which is in Tylenol) before and every 6 hours for 24 hours after being vaccinated. Those participants showed fewer of the mild side effects.
The team found that the experimental vaccine produced neutralizing antibodies — or antibodies that can not only latch onto the virus but also block it from infecting cells — in 91% of the participants (32 out of 35 tested) who received a single dose of vaccine and 100% in those who received two doses. The vaccine also raised the level of T-cells that recognize SARS-CoV-2. T-cells are a group of white blood cells that may directly kill the virus or ramp up other parts of the immune response to fight it.
"There is still much work to be done before we can confirm if our vaccine will help manage the COVID-19 pandemic, but these early results hold promise," co-author Sarah Gilbert, a professor of Vaccinology at the University of Oxford, said in the statement. "As well as continuing to test our vaccine in phase 3 trials, we need to learn more about the virus — for example, we still do not know how strong an immune response we need to provoke to effectively protect against SARS-CoV-2 infection." (Gilbert's three children, 21-year-old triplets, are taking part in the clinical trial, Bloomberg News reported.)
The authors also noted that more research is needed to replicate the results in different groups of people (91% of the participants in the trail were white and the average age was 35 years old). The team will follow-up with these participants for at least a year, but is now also recruiting volunteers for ongoing phase 2 and phase 3 trials in the U.K., Brazil and South Africa, according to the statement.
Today, Chinese researchers also reported similar results in The Lancet for another experimental vaccine, also based on a weakened adenovirus. This group used an adenovirus that typically infects humans, rather than chimpanzees. The new study also didn't find serious adverse events. More than 90% of the participants in their phase 2 trial developed T-cell responses and about 85% developed neutralizing antibodies.
"The results of both studies augur well for phase 3 trials, where the vaccines must be tested on much larger populations of participants to assess their efficacy and safety," Naor Bar-Zeev and William J Moss, both part of John Hopkins' International Vaccine Access Center, wrote in an accompanying commentary in The Lancet. "Overall, the results of both trials are broadly similar and promising."
Oxford is continuing to study this candidate vaccine in its ongoing phase 2 and larger phase 3 trials and has already partnered with AstraZeneca to mass produce doses of the virus. The team is also planning to start the long-controversial challenge studies — in which they would deliberately expose healthy volunteers to the coronavirus after they have been given the experimental vaccine — within months, either in parallel with their phase 3 trial or after their phase 3 trial is completed, according to The Guardian.
The Oxford vaccine is one of nearly 200 vaccine candidates being developed around the world to prevent infection by the novel coronavirus. Last week, U.S.-based biotech company Moderna, in partnership with the U.S. National Institutes of Health, also published promising early results from the phase 1 trial of its candidate vaccine in The New England Journal of Medicine. This vaccine also appeared safe, well-tolerated and prompted neutralizing antibodies, according to a previous Live Science report.
Originally published on Live Science.