That, in turn, could delay the immunization of the 450,000 high-risk residents over 75 — nearly triple the number of residents vaccinated since the state’s rollout began last month.

Governor Charlie Baker said the state would ask its COVID-19 advisory panel to consider whether to lower the age limit to 65 for the next round of vaccines.

“These workers are out in the community and should be vaccinated as soon as they can,” said Lisa Gurgone, executive director of Mass Home Care, which provides services to about 60,000 homebound seniors across the state.

But residents over 75 who live in low-income senior apartments run by public housing authorities and some nonprofits are waiting to learn when and where they’ll be vaccinated.

“You’ve got this patchwork approach,” said Andrew DeFranza, executive director of Harborlight Community Partners, a nonprofit that operates a half-dozen subsidized senior housing sites in Beverly, Rockport, and Ipswich.

“These are very frail, very vulnerable people who live in affordable senior housing but are not yet eligible to receive vaccines.”.

But the logistics got more complex this week when the state designated 119 smaller and more dispersed sites, including schools and senior centers, to inoculate first responders such as police, firefighters, and emergency medical technicians.

The challenges will multiply again when injections begin for the over-75 residents living independently or in senior housing not covered in Phase 1 vaccinations, a group larger than the first three combined.

“Everyone feels we can’t get it quick enough,” said Elissa Sherman, president of Leading Age Massachusetts, which represents aging service providers and nonprofit senior housing operators.

Vaccinations of first responders will start there Thursday, initially serving about 300 people a day but eventually ramping up to about 5,000 a day and “potentially much bigger numbers than that over time,” Baker said.

Baker said his COVID-19 advisory committee would study the plan, though other governors, including Governor Andrew Cuomo in New York, said they’ll be dropping eligibility to age 65.

The pharmacy companies have also started clinics this week at rest homes as well some private senior living sites and continuing-care retirement communities, where residents have access to multiple levels of care on a single campus.

People are hungry for it,” said Amy Schectman, president of 2Life Communities, who said residents have been mostly confined to their rooms at her organization’s subsidized senior living sites in Brighton, Brookline, Newton, and Framingham

But residents of other affordable housing units, including those operated by more than 200 public housing authorities, weren’t given the opportunity to sign on with the federal pharmacy program — and they don’t know why

“Our residents are some of the lowest income seniors in the state, and they have yet to be placed on a schedule where they can be vaccinated and return to some normality,” said David Hedison, executive director of the Chelmsford Housing Authority and president of the Massachusetts chapter of the National Association of Housing and Redevelopment Officials

“All seniors in subsidized housing should be receiving the vaccine.”