New York City Mayor Bill de Blasio strongly encouraged vaccinated people to wear masks indoors but stopped short of reissuing a mask mandate on Monday, spurning guidance from the U.S. Centers for Disease Control and Prevention."We want to strongly recommend that people wear masks in indoor settings even if you're vaccinated," de Blasio said. "If you don't know the people around, if you're not sure if they're vaccinated or not, or if you know some are unvaccinated, it's absolutely crucial to wear a mask even if you are vaccinated."Still, he did not require masks in all indoor settings, a step that Washington D.C., Los Angeles County and some other large metro areas have taken. Already, New York City requires vaccinated people to wear masks on public transit, in hospitals and in schools.Last week, the CDC issued new guidance that fully vaccinated people should wear masks indoors when in areas of "substantial" or "high" COVID-19 transmission, a metric based on case rates and positivity rates in a county. All five boroughs in NYC are in areas of "substantial" or "high" transmission.De Blasio's decision not to reissue a mask mandate reflects the waning influence of the CDC at this point in the pandemic, when protective vaccines are widely available for everyone 12 and older.The CDC's new mask guidance was based on an outbreak of the delta variant among mostly vaccinated people in Provincetown, Massachusetts, in which five people were hospitalized and no one died. The vaccines, though not 100% effective, provide substantial protection against severe illness and death.In recent weeks, the mayor has emphasized the importance of vaccinating as many people as possible and downplayed the use of masks, saying vaccines are "the whole ball game.""Masks can be helpful, we are going to delineate to New Yorkers the best way to use masks, but they don't change the basic reality. Vaccination does," he told CNN on Friday.About 55% of all NYC residents are fully vaccinated, according to city data, a number higher than the total U.S. rate of about 50%. The rate differs by borough, however: about two-thirds of Manhattan residents are fully vaccinated, while only 46% of Bronx residents can say the same.Mayor de Blasio said Monday the city still plans to focus its efforts on raising vaccination rates. "Everything we do is vaccine-centric," de Blasio said.The city has offered both carrots and sticks to encourage vaccinations. Any resident who gets a first dose of the vaccine at a city-run vaccination site will get $100. At the same time, all unvaccinated city employees will be required to start weekly testing on Sept. 13.The mayor also announced Monday that every new employee for the city of New York will be required to prove they are vaccinated before they can begin work.