A vaccine candidate developed by scientists in the United States performed well in an experiment that pitched it against the most common mutation of the coronavirus , according to a new study. The product, manufactured by Moderna, a biotechnology company based in Massachusetts, was tested on a modified strain that simulated the D614G mutation of the coronavirus Research has shown this is present in more than 70 per cent of the confirmed infections around the world, and in close to 100 per cent in some European countries. Compared to other strains, D614G produces more viral copies in the respiratory tract and spreads more efficiently from person to person. What the US researchers, led by Professor Drew Weissman from the University of Pennsylvania, sought to find out was if the mutation could evade a vaccine-induced immune response. Their methodology involved injecting the Moderna vaccine into humans, monkeys and mice, then collecting blood samples a few weeks later, after antibodies had been produced. What they found was that the antibodies were up to four times more likely to bind to the pseudovirus if it had the D614G gene than if it did not. “This is not an escape mutation that would impede current vaccines,” the researchers in a paper published on Friday on the preprint website Medrxiv.org, which means it has not been peer-reviewed. But they said they were not surprised by the results. That is because, according to the study, the mutation makes a subtle change to the virus’ spike protein, which makes it easier to bind with a receptor on the host cell. But that also increases the chances of antibodies binding with the virus. “The gain in infectivity provided by D614G comes at the cost [to the pathogen] of making the virus more vulnerable to neutralising antibodies,” Weissman said. His collaborators were from Duke University, Harvard Medical School and Los Alamos National Laboratory. The Moderna vaccine candidate is likely to be among the first US products to enter phase 3 clinical trials, with tests set to start this week. According to the World Health Organisation , there are at least 25 coronavirus vaccine candidates in clinical trials around the world. Most of them are based on the first viral sequence released by Chinese scientists in early January, which does not have the D614G mutation. D614G has been detected in China, but it is quite rare. A study by Chongqing Medical University last month found the antibodies produced by recovering patients in China had difficulty neutralising a strain with the mutation, and in one patient there was no effect at all. The Chongqing study produced similar results to those found by IBM’s AI medical team, which used computer modelling. What happens next, as coronavirus vaccine trials move to a new phase? While the research led by Weissman offers fresh perspective and hope, it is also “quite confusing”, according to a government epidemiologist in Beijing. “This could be potentially good news, but it’s too early to celebrate without direct proof,” said the person, who asked not to be named. A separate study by researchers at the University of California, Berkeley found the D614G strain had also acquired additional mutations and evolved into two distinct clades, one that is dominant in the United States and the other in Europe. Mortality rates increased when the two strains circulated together in the same community, the researchers said. That was possibly a result of serial infection by different D614G strains fooling the human immune system into producing too many antibodies and triggering a fatal inflammation. A limitation of the US study was the use of a pseudovirus, which replicates only once after host cell entry. The results could therefore be different to what happened in real life, the researcher said.