Moderna has developed an improved version of its mRNA vaccine against COVID-19 called mRNA-1283. This streamlined vaccine is effective at lower doses and has a longer shelf life when stored in a refrigerator. Unlike existing COVID-19 vaccines that consist of the entire spike protein, mRNA-1283 only includes two key parts of the spike protein. These two parts contain the essential sites to which the most effective antibodies against the SARS-CoV-2 coronavirus bind. By focusing on these key sites, the vaccine generates a stronger antibody response. Animal tests have shown that combining these two parts produces a better response compared to when they are separate. In a human trial, even a tenth of the standard dose of Moderna’s original COVID-19 vaccine produced an antibody response as strong as a full dose. As a result, lower doses have been selected for subsequent clinical studies. Additionally, the shorter mRNAs in mRNA-1283 make it less likely to degrade, giving the vaccine a longer shelf life compared to mRNA-1273. The vaccine is currently being tested in a trial that includes key sites from the original SARS-CoV-2 virus as well as the BA.4 and BA.5 omicron subvariants. It can be updated to target newer variants if regulatory approval is received. The latest mRNA booster shots now being administered target the XBB.1.5 omicron subvariant, and they no longer contain the original virus. The US and UK have approved booster vaccines targeting the XBB.1.5 omicron subvariant. However, in the UK, stockpiled vaccines targeting older variants may still be used for some individuals receiving boosters.
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