A first of its kind Lyme disease vaccine trial ran into a road block last weekend as the developers announced they had discontinued the study for about half of the thousands of participants in the U.S. — including those on Martha’s Vineyard.

The clinical trial, developed by pharmaceutical giant Pfizer in partnership with the French company Valneva, started last summer in 50 Lyme-endemic communities. The Vineyard, which has rates of Lyme disease nearly 10 times as high as the rest of the state, was selected as a trial site.

On the Vineyard, several hundred participants took part in the study, getting injections at clinic sites at the Martha’s Vineyard Regional High School and Vineyard Medical Care in Tisbury.

The discontinuation, according to Pfizer, was not due to any safety concerns with the vaccine and wasn’t prompted by a “participant-reported adverse event.”

Rather, the companies announced they had discontinued the study after they learned of violations in clinical practice standards by Care Access, a third-party company used to run some of the trial sites.

A Pfizer spokesperson on Tuesday would not confirm that the Vineyard trial was one of the sites that had been shut down, but Islanders involved with the study said that they had been notified this weekend about ending the trial.

“Unfortunately, your study site is one of the sites operated by this third party, and this means that your participation in the study will need to end early,” an email to a participant read. “You will not receive any further doses or provide additional blood samples.”

Participants on the Vineyard and other canceled sites, including Nantucket, are asked to continue to report any changes in health or side effects. Trials at other sites will continue, and at the end of the study, all participants will be told if they were in the placebo group or not.

On an Island where Lyme disease has reached epidemic proportions, the cancellation was a huge disappointment.

“It’s a real shame,” said Dr. Michael Loberg, the president and CEO at Vineyard Medical Care. Dr. Loberg is also on the Tisbury board of health and has long been involved with tick-borne disease prevention on the Island. “The drug certainly appeared safe and had promising efficacy.”

Most people in the trial on the Island had received at least one or two injections. Officials at Care Access, the third-party company that was running the trials at several sites including the Vineyard, previously told the Gazette that there would be three shots altogether.

While Pfizer never pinpointed the alleged violation that halted the studies, the stoppage seems to be connected to data collection. In a statement, Pfizer said that integrity of data collected in clinical trials is “critical to provide evidence and confidence in a potential vaccine or medicine’s safety and efficacy.”

In its own statement, Care Access said it was committed to patient safety and data integrity and disagreed with Pfizer’s decision to pull the plug on thousands of study participants.

“We are most disappointed for the study participants and are heartbroken about the impact this will have on the underserved communities that we reached and with whom we partnered,” Care Access wrote.

Dr. Loberg said he believed there was an audit that found some sites were not collecting data with the precision or reliability deemed necessary. The net result was Pfizer cutting any sites using Care Access.

He was not aware of any flaws involved with the Vineyard trials.

“We and our patients here did nothing wrong,” Dr. Loberg said. “It’s a real shame for those in the trial. It’s just heartbreaking.”

But Dr. Loberg said it is good that Pfizer will let people know if they were part of the placebo group, potentially allowing them to be involved in further studies. Eventually, he hoped that trials could be rekindled on the Island, or that the vaccine could be proven safe and effective enough to go to market.