As the COVID virus continues to change, the vaccines that prevent serious illness need to change too. The Food and Drug Administration (FDA) scientific advisors have recommended that new vaccine formulations should target the most common current variants of the virus, named XBB.1.5 and XBB.1.16. The mRNA vaccines produced by Moderna and Pfizer targeting the XBB variants are currently undergoing testing and should be available by the fall. Both the FDA and the World Health Organization are recommending that the vaccines only contain XBB sequences and not the ancestral COVID virus sequences in the original and the later bivalent vaccines.
One reason for this recommendation is that repeated shots of the older vaccines are thought to favor immune responses to the original sequence rather than any new variant sequence included in a bivalent (older + new variant) booster. This means that future COVID vaccines are likely to change each year (or, perhaps, more frequently) to match the dominant variant at that time, much like the flu vaccine changes each year, and to contain only one variant sequence.
Also like the flu vaccine, predicting the right vaccine formulation in time for manufacturing and distribution is a guessing game, and the rapid appearance of a new and distinct virus variant can upset this strategy.
Protection against hospitalization conferred by current mRNA COVID vaccines seems to wane after six months, particularly in the most vulnerable older individuals. A protein vaccine produced by Novavax may produce more durable responses, but data are lacking on how it might work on individuals who have received multiple doses of mRNA vaccines.
Stay tuned as more information is gathered and be prepared to roll up your sleeves again this fall.