New York City on Thursday will begin a door-to-door effort to inoculate homebound seniors against COVID-19 with the new Johnson & Johnson vaccine, Mayor Bill de Blasio announced.

FDNY officials will start outreach at retirement communities in the Bronx and Brooklyn in an effort to get elderly residents the single-dose shots, de Blasio said at a press briefing.

“We’re going to be using the Johnson & Johnson vaccine immediately to help homebound seniors,” he said. “We’re going to naturally occurring retirement communities, places where a lot of seniors live — some of them are homebound and need that help — literally house by house, apartment by apartment.”

“Right now outreach is being made, doors are being knocked on,” he said.

The program will begin Thursday at Co-Op City in the Bronx, then at 500 Bridgewater Court in Brighton Beach, Brooklyn, on Friday, according to de Blasio and other city officials.

The goal is to vaccinate 100 seniors on Thursday and Friday, then up to 240 per day by the week of March 15, according to the city.

Donald Phillips, an 80-year-old Co-Op City resident, said Thursday he’s thrilled to get the Johnson & Johnson jab.

“It’s my best option. Look, I’m 80, it’s not easy for me to get around, and this is what’s being offered to me so I’ll take it. What else am I going to do? I don’t want to spend my last years isolating myself in my apartment because I was afraid,” he said while waiting to sign up for an appointment.

Other seniors were more skeptical, saying they have more faith in the Pfizer and Moderna vaccines because they’ve been in use slightly longer.

“I hate the idea of being a guinea pig,” said Judith Ross, 75, who lives near Co-Op City. “With the two-dose option, lots of people have gotten that one, and they seem to be doing alright, so I have more confidence in the two-dose.”

Roughly 16,000 doses of the single-shot jabs are already “in hand” in New York City, another 8,000 are in transit and a total of 71,000 are expected to be delivered within the next two weeks, de Blasio said Thursday.

“We’re very happy to say doses have already arrived and this is very important for our fight against the coronavirus,” de Blasio said. “This is going to revolutionize our approach to getting people fully vaccinated by June … This is a big step forward.”

He added, “The vaccine is fast, it’s free. I look forward myself to getting a Johnson & Johnson vaccine.”

New York City has already administered more than 2.1 million vaccine doses, and a larger supply of Johnson & Johnson shots is expected to arrive in New York City later in the month, de Blasio said.

Hizzoner’s announcement came after the Johnson & Johnson vaccine was approved over the weekend, and after President Biden on Tuesday outlined an amped-up federal plan to get enough supply for every adult in the US by the end of May.