A: Yes. It looks like an updated formula with an XBB variant will be headed our way soon in the US.
TL;DR:
✅Fall boosters will be comprised of one (a “monovalent”) XBB strain.
✅The closely related XBB strains protect well against each other, so vaccine makers will pick one (might be XBB1.5).
✅The original SARS-CoV-2 strain will be dropped.
✅Timing and eligibility are still TBD, but the best guess is by September with wide eligibility like last fall.
The US FDA advisory panel met on June 15, 2023 to discuss the future of COVID vaccines in the US and recommended an updated formula targeting an XBB variant. In May, the World Health Organization also recommended that this year’s booster shots be updated to target one of the XBB variants, which currently comprise >95% of circulating COVID. The European Medicines Agency also recently recommended XBB-focused vaccines.
One change compared to recent boosters is that the original strain of SARS-CoV-2 will no longer be included. This year’s “bivalent” boosters were made up of half “original recipe” and half aimed at the BA.4/5 strains of the Omicron variant.
The original or “ancestral” strain has long gone extinct globally as new variants emerged and it’s unlikely ever to come back. One reason to drop the original strain is the idea of immune “imprinting”—our immune system is tilted to respond more strongly to things it has seen before. Many people have already seen the original spike protein several times through their vaccines and boosters. Keeping the original strain in the formula could encourage our immune system to spend more resources on neutralizing the older rather than new variants, which is no longer useful. Focusing 100% of the vaccine on current variants should optimize our immune response toward what’s circulating now and in the near future.
Based on both animal and human studies of updated vaccines, scientists expect the XBB boosters to improve protection against the latest variants compared to the previous formula. This should mean fewer acute infections in the first months after the booster and increased protection against severe disease and death in the longer term.
What happens if the virus mutates before the fall? Like all viruses, SARS-CoV-2 continues to mutate as it finds new ways to survive and reproduce. We can’t be sure that things won’t change by the fall. One thing in our favor is that for almost a year and a half the dominant variants have all been descendants of Omicron. This means they are genetically similar enough that an XBB-targeted booster would still be a big improvement in protection over previous formulas even if incremental mutations happen. The wildcard would be if a new strain surprises us that isn’t a close relative of Omicron/XBB. This could happen if a much older variant mutated for a long time within an immunocompromised host and then spread. We hope this is a less likely scenario, but we’ve certainly learned to be humble when it comes to predicting COVID-19. The good news is that if a more distantly related variant emerges, vaccines could also be developed to target it within a few months.
The US CDC will have the final say on vaccine recommendations for the fall, we’ll keep you updated as more info emerges. For now, the Nerdy Girls are excited about the opportunity to update our immune protection soon.
Stay safe, stay well.
Those Nerdy Girls
Links:
FDA panel recommends updating Covid boosters for the fall
FDA meeting materials (for the Big Nerds who want to see all the slides or watch the YouTube stream of the meeting)
