BOSTON (SHNS) – The nationwide race to get vaccines in arms hit an unexpected snag on Monday when federal regulators recommended a pause on the administration of the Johnson & Johnson vaccine to review six reported instances of a severe blood clot reported among the more than 6.8 million adults who received the shot.

U.S. Food and Drug Administration Acting Commissioner Dr. Janet Woodcock said the halt will likely last “a matter of days,” noting that the reported incidents appear to be “extremely rare.” In the meantime, Massachusetts will follow the federal guideline and stop using the J&J shot, requiring those who already had appointments booked to contact their providers.

Gov. Charlie Baker did not make any public appearances on Tuesday, but the impacts of the J&J change on the state’s vaccination campaign will likely be a central topic at his next press conference.

Through Tuesday, Massachusetts had administered 192,920 doses of the single-shot J&J vaccine, representing just more than 10 percent of the 1,833,085 residents who are now fully vaccinated against COVID-19. Another 1,640,165 residents have received both doses of either the Moderna or Pfizer vaccines, according to state data.

Medical experts told lawmakers on Tuesday that, while they want to see more sequencing, there is optimism that the vaccines still provide a valuable level of immunity against the more infectious COVID-19 variants spreading in Massachusetts and the country.

The Department of Public Health reported 1,401 newly confirmed cases of the virus on Tuesday from 57,829 tests. There were 714 patients in Massachusetts hospitals with COVID-19 counted in Tuesday’s report, an increase of 15 from the day prior.