COVID-19 vaccines and boosters still reduce the likelihood of serious illness and hospitalization. But they’re less effective at protecting against symptomatic COVID-19 — and at fighting the immune-evasive strains currently circulating.

Now, new guidance from the World Health Organization Technical Advisory Group on COVID-19 Vaccine Composition recommends COVID-19 boosters leave out the original “index” strain, which no longer shows up in humans, and instead focus on combating the XBB lineages currently circulating.

The group said that including the index virus (including early variants such as alpha, beta, gamma and delta) in bi- or multivalent vaccines would effectively dilute boosters: Index vaccines produce undetectable or very low levels of neutralizing antibodies to lineages that currently predominate globally, such as XBB.1.5, XBB.1.16 and XBB.1.9.

Reuters reports that major vaccine producers like Pfizer/BioNtech, Moderna and Novavax  are already working on XBB targets and should finalize their booster recipes later this year, once the FDA releases its recommendations. The agency is slated to hold a meeting of outside experts in June.

Meanwhile, just who provides and pays for vaccines and boosters remains in a state of transition; the U.S. ended its emergency declarations last week, when Arizona Public Health Association director Will Humble said “if you want to get the booster shot this fall, then you'd have to check and see, OK, who's in network for my health plan? And where can I go to get the vaccine?”