For nearly a month, the Centers for Disease Control and Prevention’s online vaccine tracker has shown that virtually everyone 65 and older in the U.S. — 99.9 percent — has received at least one Covid-19 vaccine dose.
That would be remarkable — if it were true.
But health experts and state officials say it’s certainly not.
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.
Knowing with accuracy what proportion of the population has rolled up sleeves for Covid shots is vital to public health efforts, said Dr. Howard Forman, a professor of public health at Yale University School of Medicine.
“These numbers matter,” he said, particularly in efforts to increase the rates of booster doses that have been administered. As of Sunday, about 47 percent of people 65 and older had received booster shots since the federal government made them available in September.
“I’m not sure how reliable the CDC numbers are,” Forman said, pointing to the discrepancy between state data and the agency’s 99.9 percent figure for seniors, which he said can’t be correct.
“You want to know the best data to plan and prepare and know where to put resources in place — particularly in places that are grossly undervaccinated,” he said.
Getting an accurate figure on the proportion of residents who have been vaccinated is difficult for several reasons. The CDC and states may be using different population estimates. State data may not account for residents who get vaccinated in states other than where they live or in clinics in federal facilities, such as prisons, or those managed by the Veterans Health Administration or the Indian Health Service.
CDC officials said the agency may not be able to determine whether people are getting their first, second or booster doses if they got their shots in different states or even from providers in the same city or state. That can lead the CDC to overestimate first doses and underestimate booster doses, CDC spokesperson Scott Pauley said.
In a footnote on its Covid vaccination data tracker webpage, the CDC says: “There are challenges in linking doses when someone is vaccinated in different jurisdictions or at different providers because of the need to remove personally identifiable information (de-identify) data to protect people’s privacy. This means that, even with the high-quality data CDC receives from jurisdictions and federal entities, there are limits to how CDC can analyze those data.”
On its dashboard, the CDC has capped the percentage of the population that has received a vaccine at 99.9 percent. But Pauley said the figures could be off for multiple reasons, such as potential data-reporting errors or the census denominator’s not including everyone who lives in a particular county, like part-time residents.
Liz Hamel, the vice president and director of public opinion and survey research at KFF, agrees that it’s highly unlikely that 99.9 percent of seniors have been vaccinated. She said the differences between CDC vaccination rates and those found in KFF and other polls are significant. “The truth may be somewhere in between,” she said.
Hamel noted that the KFF vaccination rates tracked closely with the CDC’s figures in the spring and summer but began diverging in the fall, just as booster shots became available. KFF surveys show that the percentage of adults who had been at least partly vaccinated changed little from September to November, moving from 72 percent to 73 percent. But CDC data show an increase from 75 percent in September to 81 percent in mid-November.
The consequences of cases will increasingly be determined by the proportion of unvaccinated and unboosted, so having a good handle on this is vital for understanding the pandemic.
Epidemiologist William Hanage, Harvard University
As of Sunday, the CDC says, 83.4 percent of adults had been at least partly vaccinated.
William Hanage, an associate professor of epidemiology at Harvard University, said such discrepancies call the CDC figure into question. He said getting an accurate figure on the percentage of seniors who have been vaccinated is important because the age group is most vulnerable to severe consequences of Covid, including death.
“It is important to get them right because of the much-talked-about shift from worrying about cases to worrying about severe outcomes like hospitalizations,” Hanage said. “The consequences of cases will increasingly be determined by the proportion of unvaccinated and unboosted, so having a good handle on this is vital for understanding the pandemic.”
For example, CDC data show that New Hampshire leads the country in vaccination rates, with about 88 percent of its population having been at least partly vaccinated. The New Hampshire vaccination dashboard shows that 61.1 percent of residents have been at least partly vaccinated, but the state isn’t counting all people who get their shots in pharmacies because of data collection issues, said Jake Leon, a spokesperson for the state Department of Health and Human Services.
In addition, Pennsylvania health officials say they have been working with the CDC to correct vaccination rate figures on the federal website. The state is trying to remove duplicate vaccination records to make sure the dose classification is correct — from initial doses through boosters — said Mark O’Neil, a spokesperson for the state Health Department.
As part of the effort, the CDC late last month reduced the reported percentage of adults in the state who had received at least one dose from 98.9 percent to 94.6 percent. It also lowered the percentage of seniors who have been fully vaccinated from 92.5 percent to 84 percent.
However, the CDC hasn’t changed its figure for the proportion of seniors who have been partly vaccinated. It remains at 99.9 percent. The CDC dashboard says that, as of Sunday, 3.1 million seniors in Pennsylvania had been at least partly vaccinated. The latest census data show that Pennsylvania has 2.4 million people 65 and older.