Massachusetts received its first vaccine to protect against COVID-19 when the shipment was delivered Monday morning at Boston Medical Center.

David Twitchell, the hospital's chief pharmacy officer, said the shipment of 1,950 vials of Pfizer vaccine has been unpacked and put in a freezer that maintains ultra-cold temperatures.

The hospital will begin administering doses on Wednesday. The first will go to doctors, nurses and front-line staff.

“The first vaccinations will be at 9 a.m. Wednesday and so away we go, " Twitchell said. "We'll vaccinate about 1,000 by Saturday or so--that would be optimistic--and 2,000 toward the end of next week.”

A total of 60,000 doses of the vaccine in various shipments arrived in the state Monday, with another 120,000 expected next week, according to Twitchell.

While the Pfizer vaccine requires two shots to be fully effective, he said the hospital will administer all doses on hand and wait for another shipment before giving anyone the second shot.

Tufts Medical Center and the Mass General Brigham hospitals are expecting their first vaccine shipments Tuesday.

Below are five things to know about the delivery of the Pfizer vaccine to Massachusetts, according to Twitchell, who said health officials will be conducting a mass outreach campaign.

1. Who is the first group of people to receive the vaccine?

Clinical and non-clinical healthcare workers doing direct and COVID-facing care are the first to be vaccinated. Long-term care and assisted living facilities and police, fire and emergency medical technicians are also in phase one of the state guidelines.

2. When can the public expect to sign up to receive the vaccine?

Hospitals and other medical facilities such as long-term care facilities will follow state guidelines for vaccinating the public as new shipments arrive. Once the supply chain expands, distribution of the vaccine and available dates will become clearer, but it looks to be around February.

Pfizer and Moderna are both a two-dose vaccine. That's not uncommon; many diseases require this. The first dose initiates the body’s immune system. When the second dose is given, the body is prepared and the effect is stronger.

3. Can a person “catch” COVID-19 after getting the vaccine and is there any cost to be vaccinated?

After getting vaccinated a person cannot get COVID from the vaccine and will be at least protected against severe symptoms of the disease, if not altogether. Mask wearing, socially distancing and limiting travel, is still advised until a larger percentage of the population receives the vaccine. There is no cost to any patient. A patient cannot be made to pay any dollar amount.

4. Should a person be vaccinated if they have an allergy or autoimmune disease and how safe is a vaccine?

Anyone with a history of severe allergic reaction that requires medical attention is excluded from obtaining a vaccine, according to the federal Centers for Disease Control. In the future, people who are on the border of having allergies need to inform their provider so they can take extra precautions. The vaccine trials conducted separately by Pfizer and Cambridge-based Moderna excluded people with a history of severe allergies. Of the 70,000 people participating in the trials in the U.S., each receiving two doses for a total of 140,000 shots, no one had an allergic reaction, so screening is important.

There is nothing that says a person with an autoimmune disease cannot be vaccinated, but talk to your provider.

These vaccines passed the same rigorous testing standards any drug would have to in order to be approved. Given this was a pandemic and federal support funded the acceleration, speed was possible. Also keep in mind there are no less than 9 systems designed to monitor the safety of this vaccine (and other vaccines). Officials continue to learn and use that to keep people safe.

5. If you are pregnant or lactating, is it safe to get the vaccine?

The CDC reviewed the guidelines and says no data or not enough data exist to know if it's safe in those situations, but it's suggested a patient get the vaccine because the benefits outweigh the risks. There is no reason to believe that the vaccine is harmful to breastfeeding infants, according to the CDC. Talk to a provider as you weigh these decisions.