Since Covid-19 vaccines became widely available, there has been a wide gap in deaths between the vaccinated and unvaccinated. But recent Covid deaths are much more evenly split as highly transmissible variants take hold, vaccine protection wanes and booster uptake stagnates.

Breakthrough infections have become more common in recent months, putting vulnerable populations at increased risk of severe disease or death as more and more transmissible variants continue to spread. This seems to be especially true for seniors in the United States, who were among the first to get their initial vaccine series.

In the second half of September — the height of the Delta wave — less than a quarter of all Covid-19 deaths were among vaccinated people, federal data shows. But in January and February, amid the Omicron surge, more than 40% of Covid-19 deaths were among vaccinated people.