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NEW YORK — Hold onto your masks.

The Centers for Disease Control and Prevention changed course Tuesday on some masking guidelines, recommending that even vaccinated people return to wearing masks indoors in parts of the U.S. where the delta variant of the coronavirus is fueling infection surges.

New guidance applies to counties with transmission rates considered “substantial” or “high.” Per the most recently available CDC data, all five New York City counties along with Suffolk and Nassau counties fall under the new guidance. The rate was the worst in Staten Island.

A CDC map from July 27, 2021 shows rates of transmission. (CDC)

Gov. Andrew Cuomo said New York would review the new recommendations from the CDC.

“New Yorkers beat back COVID before — going from the highest positivity rate on the globe to one of the lowest — by staying smart, following the science, and having each other’s backs, and that’s exactly what we’ll keep doing in this next phase of the pandemic,” he said.

Just hours before the CDC made Tuesday’s announcement, New York City Mayor Bill de Blasio doubled down on vaccinations being the key to beating the COVID pandemic.

“We can talk about masks and figure out what makes sense to make, to do about masks. but the thing that will save us is vaccination,” he said. “The thing that will change the entire environment is vaccination. The one thing I want to make sure is that folks don’t say, ‘oh, you know, because there’s new mask rules, we don’t need to think about vaccination anymore.’ No, it’s quite the opposite.”

Over in New Jersey, the new suggested CDC mask guidance applies to Bergen, Essex, Union, Middlesex, Monmouth, Ocean, Burlington and Atlantic counties. The transmission rate was high in Monmouth County and substantial in the other noted NJ counties.

A spokesperson for Gov. Phil Murphy said New Jersey would review the CDC masking guidance.

“Governor Murphy continues to encourage all individuals ages 12 and up to receive the free and effective COVID-19 vaccination to reduce the spread of the virus,” the Murphy spokesperson said.

The CDC’s website has a map that shows counties with substantial and high transmission. That includes a combined 63.11% of counties in the U.S.

The announcement reverses a decision made by the CDC just two months ago. The guidance specified that fully vaccinated people did not have to wear masks outdoors in crowds and in most indoor settings. The guidance still called for wearing masks in crowded indoor settings like buses, planes, hospitals, prisons and homeless shelters.

For months COVID cases, deaths and hospitalizations were falling steadily, but those trends began to change at the beginning of the summer as a mutated and more transmissible version of the coronavirus, the delta variant, began to spread widely, especially in areas with lower vaccination rates.