Vaccinations in Philadelphia will begin Wednesday morning at multiple hospitals in the city, officials said, as a first wave of 13,600 doses will be administered this week.

Another round of Pfizer doses could arrive in the city next week along with 27,000 doses of the Moderna vaccine if it is approved by the federal government this week, Deputy Mayor for Public Health Dr. Tom Farley said at a Tuesday news conference.

Farley also outlined six tiers of Americans that will determine how vaccine doses are distributed and administered. Those are:

1. Health care workers routinely exposed to COVID-19 patients
2. Residents and staff at nursing homes
3. "Critical infrastructure workers" who are routinely exposed to COVID-19 while on the job (police officers, firefighters, bus drivers, sanitation workers etc.)
4. Residents and workers in congregant settings that are not nursing homes
5. People with underlying medical conditions
6. The rest of the general public

Farley said the first two tiers will receive the initial tens of thousands of doses from Pfizer and Moderna, which could mean months before the next tiers begin inoculations.

"We’re going to start vaccinating in those first two groups, then refine how we vaccinate based on our own guidance and CDC guidance," he said, adding that there are tens of thousands in the city that make up the first two groups.

Inoculations against the COVID-19 infection, which on Monday passed a grim milestone in the United States, already have begun in earnest in nearby areas like North Jersey and Delaware on Tuesday.

Health care workers and the elderly in communal settings were the first to receive doses in those two states.

New Jersey Gov. Phil Murphy was on hand as University Hospital, Newark, nurse Maritza Beniquez got the first dose of the Pfizer vaccine administered in the state on Tuesday morning.

"I can see that light at the end of the tunnel," she said moments before the shot. Afterward, Beniquez -- who was celebrating her birthday -- clasped her hands and thanked God.

The initial vaccinations are just the start of months of work in what is one of the largest mobilizations for a single logistical purpose in American history. Pfizer has promised the United States 100 million doses in the next couple months, enough to inoculate 50 million Americans.

The vaccine is proven to be 95% effective, but each person must receive two doses before they are immune. The first dose is administered 21 days before the second dose.

The vaccinations can't come soon enough. On Monday, NBC News reported that 300,000 Americans have died from the coronavirus since the start of the pandemic earlier this year.

The first wave will include frontline health care workers at hospitals and longterm care facilities as well as seniors living in communal settings. They will be followed by first responders like police officers, firefighters and paramedics.

That still leaves more than 250 million Americans who will eventually need vaccinations.

The federal government hopes it will be able to receive another 100 million doses by the end of March, either through Pfizer or another pharmaceutical company, Moderna, whose vaccine is nearing submission to the U.S. Food and Drug Administration for approval, or a combination of both companies' doses.

New Jersey will receive three shipments of the Pfizer vaccine this month, beginning with about 76,000 doses this week and another 86,000 next week, Health Commissioner Judy Persichilli said Monday.

It could receive 150,000 doses by the end of next week if Moderna's vaccine is given emergency approval by the FDA soon, she said. The FDA on Tuesday gave an initial approval to the vaccine, but an independent advisory panel will need to weigh in later this week before a final okay is given.

Tuesday “is the establishment of our beachhead. It’s going to take several more months of fighting,” Murphy said.

The first doses also arrived in Philadelphia for distribution in Pennsylvania. The city will get 13,600 doses this week, and another 100,000 will go to health care facilities throughout the state in the days ahead, officials said.

In Delaware, health officials said the state received 8,775 doses on Monday in its first batch.

“The Pfizer vaccine’s arrival is the first step in a process of getting back to our pre-pandemic normal,” Gov. John Carney said. “We are all looking forward to that. The vaccine will provide our front-line health care workers with the protection they need while caring for Delawareans who have contracted the virus. The vaccine’s arrival does not mean we are in the clear. In fact, now more than ever, we need to step up our efforts to keep each other safe."

The first of Delaware's doses was given on Tuesday morning to nurse Elisabeth Cote at Bayhealth's Kent campus in Dover.

Farley said "this is clearly a historic moment in the biggest pandemic in history" and that vaccines would begin being administered at "most hospitals" in Philadelphia on Wednesday.

Asked why Philadelphia vaccinations would begin two days after they began in New York City, and a day after they began in New Jersey, he said some regions apparently received doses ahead of a schedule initially laid out by the federal government.

"I don’t think a couple days will make a big difference," he said.

The Associated Press contributed reporting to this article.