MOSES LAKE — After traveling cross country, around 2,000 miles in all, in a container colder than the interior of Antarctica, almost 1,000 doses of the coronavirus vaccine developed by Pfizer arrived Tuesday morning in Moses Lake.

Frontline medical workers, especially those at higher risk of complications from COVID-19, will begin receiving a shot in the arm of the emergency-use-authorized COVID-19 vaccine starting Thursday at Samaritan Hospital.

The shipment arrived at the hospital shortly before noon Tuesday, said Gretchen Youngren, executive director of development and communications at Samaritan. Inside the specialized, insulated shipping packages topped with dry ice is a container approximately the size of a pizza box, each of which holds 195 vials. Each vial contains 5 doses, for a total of 975 doses per box. Tuesday’s shipment contained a single one of the “pizza boxes,” Youngren said.

Going forward, Youngren said the hospital expects a shipment every week.

The Pfizer vaccine requires two doses spread out over 21 days before vaccination is fully effective, and those that receive their first dose in the coming days will finish out their vaccination with supplies from a future shipment, Youngren added.

Though state health officials expect more organizations to become distribution centers as more doses from Pfizer-BioNTech and, later, Moderna become available, representatives with the state Department of Health wrote in an email it could not currently address specifics on possible expansions to vaccine rollout.

Given the ultracold requirements of the Pfizer vaccine, which needs to be stored at around -70 Celsius, the number of facilities with the necessary equipment is limited, according to the state DOH’s webpage.

For now, Samaritan Healthcare will be the central distribution site for Grant County and surrounding communities, Youngren said.

According to guidance from the state Department of Health, vaccine supply will initially be limited, and distribution will be focused on high-risk health workers and first responders. Residents of nursing homes, assisted living facilities and other long-term care centers will also be first in line for a vaccination. The state estimated its first shipment of the vaccine would include 62,400 doses, with an additional 220,000 doses by the end of the year.

That won’t be sufficient to cover everyone in the first round of vaccinations — the state DOH estimates there are anywhere from 300,000 to 500,000 Washington residents who qualify for the first phase, each of which will require two doses.