Michael Le Page in New Scientist:
Several countries, including the US, Canada and the UK, have approved new covid-19 booster vaccines, targeting a more recent variant than the boosters used last year. Here is what you need to know.
The boosters, made by Moderna and Pfizer, consist of an mRNA recipe for making the spike protein of the XBB.1.5 variant of SARS-CoV-2. The spike protein protrudes from the surface of the virus and plays a part in infecting cells. Newer variants have changes in their spike protein that help them evade the antibodies we have to older variants. The boosters stimulate our immune systems to produce antibodies to the new versions of the spike protein.
XBB.1.5 was chosen for the boosters because it was the main variant causing infections in June, when the vaccines needed to be finalised. It has already been largely replaced by yet more new variants, but most of these are closely related to XBB.1.5, so the boosters should still provide excellent protection.
More here.