The biggest questions about the newest Covid-19 vaccines are still unanswered.

A doctor holds a bottle containing doses of the bivalent Covid-19 booster.

In early September, the Centers for Disease Control and Prevention (CDC) recommended updated Covid-19 boosters for all Americans 12 and over.

The “update” was a broadening of the vaccines’ target: In addition to aiming for the initial strain of the virus, the new boosters would also take aim at the spike protein present on newer omicron variants of SARS-CoV-2, BA.4 and BA.5.

The hope was that the new boosters (called “bivalent,” for the two strains) would provide additional protection, priming the immune system to recognize a much-mutated virus that had grown better at evading the immune system and reinfecting people.

Back in the fall, that hope was based mostly on modest data showing that the updated boosters raised antibody levels in people who received them. But a big question remained unanswered: In the real world, would the updated boosters actually prevent more cases from progressing to severe disease than the original, monovalent boosters would?

Researchers weren’t sure, and were divided on whether it was worth the $5 billion price tag to update the boosters without better data.

Now we have real-world, human data on the bivalent boosters, along with more carefully controlled lab studies. They show that over the last few months, older adults who got the bivalent booster last fall were less likely to have a Covid-related hospitalization or death in the months since than those who didn’t.

But the studies still tell an incomplete story because of how their data was gathered. Scientists don’t yet have totally clear answers to all questions about the booster.

Here’s what the latest available data on the vaccine booster shows and what it doesn’t — and how future studies should change to more precisely chart a path forward.

READ FULL ARTICLE