LONDON — Two candidate vaccines, including a closely watched one being developed at the University of Oxford, showed positive trial results Monday against the virus that causes COVID-19, making it more likely that a safe, effective vaccine can be developed quickly.
They add to two small, previous studies on different vaccine candidates in the U.S. that also appeared to be relatively safe and to trigger appropriate immune responses in study subjects.
Early stage trials only explore safety and dosing and cannot determine a vaccine’s effectiveness, but signs indicate that all four candidate vaccines are leading to immune responses similar to those experienced by people infected with the SARS-CoV-2 virus.
There are currently about 17 candidate vaccines being tested in people around the world.
The new results showed Oxford University and drug company Astra Zeneca’s candidate vaccine, AZD-1222, led to strong immune responses for nearly two months in a trial that continues to track more than 1,000 healthy adults. A second dose, given to 10 patients, seems to have boosted their immune response further without adding significant side effects, according to a paper published Monday in The Lancet.
Half the volunteers were given the SARS-CoV-2 vaccine and half were given a meningitis vaccine. The so-called AZD-1222 vaccine caused more side effects considered minor than the meningitis one, but acetaminophen relieved most of the effects, the study found.
Dr. Anthony Pollard, professor of pediatric infection and immunity at the University of Oxford and chief investigator on the study, told reporters in a Zoom call the results were “an important milestone on the path to a development of a vaccine.”
The results in various clinical trials cannot be compared against each other, but the fact that all have shown strong immune responses suggests “that we might have multiple hits on target,” Pollard said.
He and other scientists leading the study stressed much more work needed to be done, including gauging how well the vaccine could ultimately potentially protect the general population from falling ill with coronavirus. Indications of that will only come with further trials on a larger group of people.
The next stage of trials in Britain will involve 10,000 people. In the U.S., 30,000 people will take part. And in Brazil and South Africa, about 7,000 people will test the efficacy and safety of the vaccine. If everything goes to plan, the vaccine could be rolled out widely by early next year, according to the Oxford Vaccine Group.
AstraZeneca CEO Pascal Soriot expects 50,000 will be vaccinated by the end of the year.
“Our hope is we can start delivering vaccine before the end of the year,” Soriot said. How soon, he said, depends on the infection rate in places where their studies are underway. Trials need enough people to become infected in order to see whether their candidate vaccine is effective.
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The Oxford-Astra Zeneca vaccine uses a weakened chimpanzee cold virus to carry a protein from SARS-CoV-2 into human cells. Once there, it triggers the person’s cells to produce the spike protein found on the surface of SARS-CoV-2, causing the immune system to recognize and attack the virus.
Nearly a month after receiving a shot, 32 of 35 participants tested showed they had developed neutralizing antibodies to SARS-CoV-2 – the kind of immune response that is believed to be essential to provide protection. None of the participants had COVID-19, so it’s not clear whether they were actually protected against it. Only a larger, Phase 3 trial, several of which are slated to start this summer, will show actual protection.
About 70% of participants in the Oxford-Astra Zeneca trial suffered fatigue and headache after the AZD-1222 shot, compared to only 41%-48% of those who received the meningitis vaccine. Among the 10 people who received an extra dose of the COVID-19 vaccine, side effects were less common after the second dose.
The study’s authors recommended that the vaccine should now be tested in older adults, who have weaker immune systems and are more vulnerable to bad cases of COVID-19.
Adrian Hill, another researcher, said it would be useful to compare different vaccine results being produced in labs around the world and even to test those vaccines in the same lab. He said this would help greater understanding of how to assess the interim successes of researchers.
The second study published Monday in The Lancet looked at a Chinese vaccine candidate tested in more than 500 people, including a small number older than 55. The goal of the study was to evaluate the immune response and safety of the vaccine and determine a dose that would be used in a larger phase 3 trial.
Of the 508 participants, 253 received a high dose, 129 received a low dose and 126 a placebo.
The Chinese vaccine candidate works almost the same way as the Oxford-Astra Zeneca one, but uses a weakened version of the human common cold virus – rather than a chimp virus – to deliver the SARS-CoV-2 protein. Half of the trial participants were already immune to the human cold virus, which is expected to limit the vaccine’s effectiveness.
The trial found that 95% of those who received a high dose of the candidate vaccine and 91% of those who received a low dose showed an immune response 28 days after the shot. Nearly 60% showed a neutralizing antibody response, which is believed to be essential to provide protection against SARS-CoV-2.