COVID-19 vaccination rates are lagging in parts of Minnesota as the pace of new shots slows throughout the state, an early warning sign that achieving herd immunity could take longer in some places.

The expansion of eligibility to anyone 16 and older on March 30 created an initial clamor for vaccine appointments, with some metro area residents driving hours to get a shot. But others who live outside the Twin Cities have not been as enthusiastic.

While the number of metro residents who've received at least one dose soared 56% since eligibility opened up, 15 of Minnesota's 87 counties saw growth rates of less than 15%, according to a Star Tribune analysis of Minnesota Health Department data.

As of last week, 2.4 million, or 55%, of eligible state residents had received at least one shot, while eight counties showed single-dose numbers below 40%. Benton and Isanti counties, both at 33%, were the lowest, state Health Department figures show.

Minnesota has set a goal of 80% vaccination coverage to tame the transmission of the coronavirus, but it is unlikely that spread will stop completely once that target is reached, especially in areas where vaccinations fall short.

"We should get to a point where we reach 80% coverage in the state and then we will still have pockets … where we could expect to see a greater chance of COVID transmission and we have to be alert to that," said state infectious disease director Kris Ehresmann.

State and health care officials expected to see a shift away from the intense demand that accompanied the initial arrival of the vaccines.

"We've always known that this point would come in the vaccination effort," said Health Commissioner Jan Malcolm. "This is not unexpected [but] perhaps a little earlier than we had hoped or thought."

Some health care systems are adding vaccination sites outside clinics and hospitals in an effort to bring the shots closer to where people live. They also are targeting low-risk individuals who previously had been told to be patient while groups more vulnerable to COVID-19 complications had priority.

"Some might have taken that wait thing a little bit too much to heart and now we want them to step to the front of the line," said Dr. George Morris of St. Cloud-based CentraCare.

Vaccinators across the state, including Mayo Clinic, CentraCare, Sanford Health and Essentia Health, report that it is taking longer to fill appointment slots despite an ample supply of vaccines.

"When the eligibility opened up it was a bit like a dam breaking and we were at a gush," said Alyssa Carlson, hospital pharmacy manager at Sanford Health Bemidji. "The river is very much flowing, it is just that the pace is not as strong as the initial break."

The vaccination slowdown began as new daily case counts rose above cautionary levels before more recently trending down. On Saturday, the Department of Health reported 2,104 new COVID-19 infections and eight more deaths, bringing the pandemic totals to 566,687 cases and 7,072 fatalities.

Vaccine hesitancy

As would be expected, areas that lead in vaccination rates, such as Olmsted County with 71% of those eligible getting at least one dose, are seeing a slowdown.

"For the first time we had open appointments available at the time we started our clinic," said Graham Briggs, director of Olmsted County Public Health. "There are some people that are not interested in getting vaccinated right now."

Residents are asking about vaccine efficacy and risks, despite research that shows the shots prevent symptomatic illness with few side effects.

The U.S. Census Bureau has been surveying Americans about hesitancy to take the vaccine. About 13% of Minnesotans said they won't get vaccinated, according to the latest bureau research conducted at the end of March.

But that number has been trending down from 21% as people become more familiar with the vaccines and observe the experiences of family and friends.

Public health officials hope to keep driving it lower.

"We certainly know that as we move past the eager beaver stage of vaccination that we are going to have to address issues of hesitancy and questions about the vaccine," said Ehresmann.

The next few weeks should reveal how close some Minnesota counties come to seeing demand slow to a trickle.

"We're getting a little closer to a saturation point," said Mike Boeselager, vice president of support services at St. Luke's in Duluth, which last week put out an appeal to fill its vaccine slots. "The question is, what is that point?"

Still some outliers

Even if Minnesota reaches a high rate of vaccine acceptance, there still could be pockets with much lower rates, especially in a state that ranks 12th largest in the country by total square miles.

Although more than 90% of Minnesota schoolchildren are vaccinated against measles, the state saw one of the worst measles outbreaks in the country in 2017, sickening 75, mostly children.

That outbreak shows what can happen when an infected person, in this case someone who picked up the disease in a foreign country, crosses paths with someone who is unprotected. The highly infectious disease was passed on to a child from the Somali American community, where measles vaccination rates among 5-year-olds had dropped to about 40%.

The disease progressed within the Twin Cities area, but it branched out to rural Minnesota when an unvaccinated child from Crow Wing County crossed paths with an infected person on a family trip to the metro. More infections were sparked when that family then traveled to Le Sueur County for a gathering.

The Census Bureau research shows that COVID-19 vaccine hesitancy is more prevalent in rural Minnesota counties. Although population density is much lower outside the metro, an infectious disease still can spread rapidly.

"In rural areas, the fact is you are still moving around, you are still coming into contact with people," said Dr. Mark Roberts, professor of health policy and management at the University of Pittsburgh Graduate School of Public Health. "If only 40% of the people in that geographic area are vaccinated and immune then you have a higher likelihood of picking up the disease."

But those outbreaks could be controlled through contact tracing and quarantines if caught early.

"If we get an outbreak in a specific county or workplace we can manage it as an isolated one and it is unlikely to spread," said Morris. "We still would have a large portion of the state vaccinated so it won't ripple throughout the whole state."

The state's herd immunity goal won't be reached until the 1.2 million children who currently are not eligible for the vaccine get their shots, a process that will unfold in stages into next year as clinical trials are completed. Those who tested positive for COVID-19 will also have immunity.

There are also questions about the impacts of virus variants, and until vaccination rates increase substantially across the globe, SARS-COV-2 will remain a threat.

"We still have quite a ways to go," said Ehresmann. "This is not going to be a situation like smallpox where this virus is eradicated from the globe. We look to get to a place where it is controlled and likely to be endemic."

Glenn Howatt • 612-673-7192

Twitter: @GlennHowatt

Correction: A previous version of this article incorrectly stated one of the two counties with the lowest percentage of eligible Minnesota residents who have received at least one dose of COVID-19 vaccine.