The first “tweaked” vaccine against the worrying coronavirus variants that emerged in South Africa and Brazil has successfully neutralised them in laboratory trials, the US company Moderna has said. The results of the small trial suggest that boosters against the variants will be feasible and could be rolled out this year to counter the threat from variants that have appeared around the world and are feared in some cases to be more transmissible or partially vaccine-resistant. Leading companies have been racing to produce adapted versions of their Covid vaccines. Pfizer/BioNTech, which has a similar mRNA vaccine to Moderna’s, and Oxford/AstraZeneca are also in the process of developing tweaked vaccines against the South African variant, B1351, and the Brazilian variant, P1, which appear to be the major threat to current immunisation programmes. Moderna became the first to announce results on Wednesday night. They appear to be very positive, although only basic information from an initial analysis of results is available so far. The US company has tested both a booster shot of its standard Covid vaccine and also a tweaked version of the vaccine in people who have previously had the full double dose. Twenty adults were recruited for each arm of the trial, or 40 in total. Two weeks after the new jab, Moderna says both the booster shot and the tweaked vaccine increased the antibodies in the blood that can neutralise the two variants of concern. But the tweaked vaccine – called mRNA-1273.351 and designed specifically to combat the South African and Brazilian variants, which have similar mutations to the spike protein – produced higher levels of neutralising antibodies than the standard booster shot, mRNA-1273. Moderna says it is also running a trial in which people are given a mixture of the booster and the vaccine specifically designed against the variant. It has submitted the early results as a paper to a pre-print server, it said in a statement. Once the combined trial is complete, it will produce a paper that will be published with peer review. “As we seek to defeat the ongoing pandemic, we remain committed to being proactive as the virus evolves. We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants,” said Stéphane Bancel, CEO of Moderna. “Our mRNA platform allows for rapid design of vaccine candidates that incorporate key virus mutations, potentially allowing for faster development of future alternative variant-matched vaccines should they be needed … We will continue to make as many updates to our Covid-19 vaccine as necessary to control the pandemic.” The vaccines have not been trialled in the field; these are blood samples analysed in the lab. But the regulatory authorities have said they would not need to go through the rigorous large-scale trials that were necessary for the original vaccines to obtain emergency approval. The company said there were few side-effects from the vaccines and those that were reported were mild. Apart from pain at the injection site, the most common reported side-effects were fatigue, headache, muscle pain and joint pain.