Uniformed correction officers will initially be excluded from the new mandate because of the ongoing staffing crisis at Rikers Island, but they will be required to get vaccinated by Dec. 1, the mayor said.The new mandate, reported first by The New York Post, builds on a July announcement that all city employees would be required to show proof of vaccination or submit to weekly testing. More than 70 percent of city workers affected by the new mandate have already received at least one dose of the vaccine, the mayor’s office said.But vaccination rates vary among city agencies. The Department of Corrections has the lowest vaccination rate, with only 50 percent of workers having received at least one dose of a vaccine as of last week, according to city data. The second lowest rate is at the city’s housing authority, where 58 percent of employees are vaccinated. The city’s fire department, emergency medical services and sanitation workers have similar vaccination rates among their workers; only about 60 percent have received at least one dose. The city’s police department has a somewhat higher rate of vaccination, with 69 percent of its workers having received at least one dose.What to Know About Covid-19 Booster ShotsWho is eligible for a booster shot?The F.D.A. authorized booster shots for a select group of people who received their second doses of the Pfizer-BioNTech vaccine at least six months before. That group includes: vaccine recipients who are 65 or older or who live in long-term care facilities; adults who are at high risk of severe Covid-19 because of an underlying medical condition; health care workers and others whose jobs put them at risk. People with weakened immune systems are eligible for a third dose of either Pfizer or Moderna four weeks after the second shot.Will people who receive Moderna and Johnson & Johnson vaccines be eligible?What underlying medical conditions qualify for a booster shot?The C.D.C. has said the conditions that qualify a person for a booster shot include: hypertension and heart disease; diabetes or obesity; cancer or blood disorders; weakened immune system; chronic lung, kidney or liver disease; dementia and certain disabilities. Pregnant women and current and former smokers are also eligible.What occupations are eligible for boosters?The F.D.A. authorized boosters for workers whose jobs put them at high risk of exposure to potentially infectious people. The C.D.C. says that group includes: emergency medical workers; education workers; food and agriculture workers; manufacturing workers; corrections workers; U.S. Postal Service workers; public transit workers; grocery store workers.Can I mix Covid vaccines?For now, it is not recommended. Pfizer vaccine recipients are advised to get a Pfizer booster shot, and Moderna and Johnson & Johnson recipients should wait until booster doses from those manufacturers are approved. The F.D.A. is planning to allow Americans to receive a different vaccine as a booster from the one they initially received. The “mix and match” approach could be approved once boosters for Moderna and Johnson & Johnson recipients are authorized.Can I get a flu shot at the same time as a Covid vaccine or booster shot?Yes. The C.D.C. says the Covid vaccine may be administered without regard to the timing of other vaccines, and many pharmacy sites are allowing people to schedule a flu shot at the same time as a booster dose.The vaccine mandate for Department of Education employees led to a vaccination rate of more than 96 percent among teachers. And a statewide vaccination mandate for hospital and nursing home workers led vaccination rates in those industries to jump to 92 percent as of the Sept. 27 vaccination deadline, and higher since then.Some labor leaders, representing thousands of workers, have resisted the idea of a city mandate.Patrick J. Lynch, the president of the city’s largest police union, the Police Benevolent Association, said earlier this month that his union would “continue to protect the rights of members who are not vaccinated.” But the city’s police commissioner, Dermot F. Shea, has supported a vaccine mandate for officers, though he acknowledged that it could strain the department if some officers choose to leave rather than get vaccinated.