They note that the CDC as of Sunday had recorded more seniors as having been at least partly vaccinated — 55.4 million — than there are people in the age group — 54.1 million — according to the latest census data from 2019. The CDC’s vaccination rate for residents 65 and older is also significantly higher than the 89 percent vaccination rate found in a poll conducted in November by KFF. Similarly, a YouGov poll conducted last month for The Economist found that 83 percent of people 65 and up said they had received at least an initial dose of a vaccine.

And the CDC counts 21 states as having almost all their senior residents at least partly vaccinated (99.9 percent). But several of those states show much lower figures in their vaccination databases, including California, at 86 percent, and West Virginia, at nearly 90 percent as of Monday.

The questionable CDC data on seniors’ vaccination rates illustrates one of the potential problems health experts have flagged about the CDC’s Covid vaccination data.