Initial studies have found that coronavirus vaccines — particularly without a booster shot — are much less effective against Omicron infections than other variants, although they appear to hold up well against severe disease.

This study suggests the same is true for people with prior infections, emphasizing the benefit of vaccines for this population.

By the numbers: The study found that prior infections were 90% effective against symptomatic reinfections for the Alpha variant, 92% effective for the Delta variant and only 56% effective for Omicron.

Effectiveness against hospitalization and death was 69% for Alpha, 100% for Delta and 88% for Omicron.