Montgomery County has led the D.C. region in its coronavirus vaccination rate for months, but it was nonetheless remarkable when County Executive Marc Elrich (D) on Monday announced that 99.1 percent of the Maryland county’s eligible residents — those 12 and older — had gotten at least one shot.

“These vaccination rates are the highest in the nation for communities with more than 300,000 residents,” Elrich said. “I want to thank the people of Montgomery County for believing the science and doing their part to slow the spread of this vicious virus.”

The figure seemed to mark a startling achievement against the pandemic even for a liberal, affluent community such as Montgomery, the state’s most populous county. Neighboring D.C. and Prince George’s County trailed at 80 percent and 83 percent, respectively, while Virginia’s Fairfax County recorded a rate of 89 percent.

Public health experts warn, however, that the 99.1 percent figure may not be the best marker of how protected Montgomery is against the coronavirus, which has infected 81,000 there and killed more than 1,680.

The partial-vaccination figure comes from a collection of county-level metrics tracked by the Centers for Disease Control and Prevention, and there are several reasons it might not fully reflect the reality on the ground.

There isn’t a standardized system in the United States for collecting large swaths of health information, experts note. The CDC takes in vaccination data from states, hospitals, pharmacies, federal agencies and other providers, all of which have their own ways of recording critical information such as number of doses and residency of the person being vaccinated. Reporting and recording errors can sometimes skew data, the CDC says, though there’s no evidence that’s occurred in Montgomery. In early October, North Carolina said vaccination rates in dozens of counties had to be changed because the CDC had mistakenly provided vaccination records based on where they were administered instead of who received them.

“People need to understand that this has been an incredibly complex process,” said William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health. “There are things that we do to try to align the numbers, but they don’t account for all the complications.”

Early on, when doses were scarce, some people misstated their county of residence to get shots. And more recently, hundreds of thousands of people across the country have gotten unauthorized third shots intended for the immunocompromised and others — effectively counting as a new “first shot” — by pretending they have not been vaccinated before, Moss noted. It’s unclear how many of these occurred in Montgomery, though several primary care providers in the county say they are regularly coming across patients who got third shots despite being ineligible.

For these reasons, public health experts say, vaccination trends are more valuable than absolute numbers, and more attention should be paid to the share of the total population that has been fully immunized. Per the CDC, 76 percent of Montgomery’s 1.1 million residents have been fully vaccinated.

“The one dose among eligible residents is an artificially low bar,” said Neil J. Sehgal, an assistant professor of health policy at the University of Maryland School of Public Health. “To the extent that we participate in public life in our community … the much more relevant statistic is proportion of total population.”

Montgomery’s acting health officer, James Bridgers, said Monday that the 99.1 percent figure reflects the “best-case scenario” in the county and that officials are also keeping track of data from the Maryland Department of Health, which shows that about 70 percent of Montgomery residents have been fully vaccinated. This figure is lower than the CDC estimate because Maryland doesn’t automatically capture residents who have been vaccinated out of state or federal workers who have received their doses through a federal stockpile of vaccines, said Andy Owen, a spokesman for the Maryland Department of Health. This data is recorded first by the CDC, then passed on to states.

Even if the partial-vaccination figure overstates Montgomery’s protection from the virus, the county has still consistently exceeded the state and national rates in getting shots into arms.

Part of this is because of Montgomery’s “relative privilege,” Sehgal said.

Across races and political affiliations, members of the working class are less likely to trust the vaccine and have access to it if they do, according to research from the Kaiser Family Foundation.

Montgomery in 2019 had a median household income of $108,820, far higher than the national average. It consistently ranks as one of the most educated communities in the country, with about a third of adults holding graduate degrees. Trust in science is high, and many residents were able to take time off to get vaccinated earlier this year when doses were still scarce. In Maryland, Montgomery’s rate of fully vaccinated residents is second to only Howard County — one of the wealthiest jurisdictions in the nation, with a median household income of more than $120,000 a year.

“Half a year ago, Montgomery residents got a jump-start on their neighbors,” Sehgal said. “That’s still showing.”

The county is home to 18 federal agency headquarters, six hospitals, dozens of nursing homes and a host of other large organizations that were able to offer vaccinations to employees at their workplaces and are now subject to President Biden’s vaccination mandates. Montgomery’s sprawling school system has made it compulsory for all employees to be vaccinated, and the county government is weighing legislation that would extend that mandate to all county employees.

Local officials also say that they’ve been able to reach needy residents in the majority-minority county by establishing an “equity framework” for vaccine distribution early on.

In the winter and spring, Montgomery reserved doses for vulnerable residents and opened up eligibility at a slower rate than its neighbors, resisting pressure from members of the public scrambling to get shots. Officials poured millions into outreach efforts for marginalized groups, dispatching mobile vaccination vans to low-income apartment complexes, enlisting the help of community clinics and rolling out ad campaigns targeting the Latino immigrant population.

Yawning gaps in vaccination rates among racial groups have dramatically narrowed, though civic organizations and nonprofits say more needs to be done. As of this week, at least 10 Zip codes in the county — most of them along Montgomery’s border with D.C. and Prince George’s — have vaccination rates of 68 percent or lower.

Grace Rivera-Oven, co-founder of the Upcounty Consolidation Hub, which serves primarily immigrant communities, said her staff receives calls daily from residents asking how they can get vaccinated. In September, Mary’s Center, which provides health care to immigrant Latino communities in D.C. and Maryland, administered nearly 450 shots in its Silver Spring clinic, said spokeswoman Lyda Vanegas. Clinicians are still seeing dozens of patients daily who have yet to get their first dose.

“We do worry that people will feel like everyone in Montgomery is vaccinated, so they can go out and not adopt other precautions,” Vanegas said. “That’s a constant worry for us.”