Emerging variants of the virus that causes Covid-19 have triggered concerns that the vaccines developed to date will not provide the high level of protection seen in clinical trials. Concerning variants have been identified in California, South Africa, Brazil and the UK. But not every variant needs a new vaccine, since vaccines produce a broad immune response that will probably cover many mutations. Here’s what needs to be done to assess whether a vaccine needs to be tweaked, and how to tweak it. Detection To confront a new variant, you need to detect it first. Surveillance is key, so scientists need to be constantly vigilant and engage in international cooperation, like they do for the influenza virus. Manufacturers of approved vaccines – including Pfizer/BioNTech, Moderna and Oxford/AstraZeneca – are looking at ways to improve their vaccines so they are ready for any variant. Comparison Once a variant of concern has been identified, scientists need to check whether existing vaccine efficacy has diminished significantly. In the case of the variant discovered in the UK, scientists were confident the vaccines already available worked well against it, but for the one discovered in South Africa the data is far less encouraging. Modification If a vaccine tweak is required, the technology used in the vaccine determines how quickly and easily the modification can be made. For example, the mRNA vaccines made by Pfizer/BioNTech and Moderna are much easier to tweak than traditional vaccine technologies. Production BioNTech has said it can produce a fresh vaccine within six weeks of a decision being made. But the Oxford/AstraZeneca team, which uses more traditional viral vector technology, says that while it can make a new formulation in days, it takes much longer to produce. It expects to have a vaccine designed to address the variant discovered in South Africa ready by autumn. Trials How extensive the trials of modified vaccines will need to be is unclear. In the case of flu vaccines, regulators do not require large-scale trials but instead are satisfied by smaller studies to show they work as well as the original vaccine. This is probably what will be expected of Covid-19 vaccine makers. Approval The new vaccine will need to be approved by regulators. In the UK, the Medicines and Healthcare products Regulatory Agency (MHRA) has said it is in talks with vaccine manufacturers about the approval process for a new jab. “We can say at this stage that it is unlikely that a full new approval process will be needed,” a spokesperson said last month. “No vaccine will be authorised for supply in the UK unless the expected standards of safety, quality and effectiveness are met.”