With the beginning of winter roughly a week away, major cities across the U.S. are looking to mask up once again for the purpose of combating not just COVID-19, but the flu and the respiratory illness RSV.

Philadelphia has imposed a temporary mask mandate for students and school staff when they come back from winter break in January. For two weeks, they will be required to wear face coverings, Superintendent Tony Watlington announced Wednesday.

"Many of us will be involved in quite a few social gatherings over the next few weeks," Watlington explained at a news conference, as reported by local WHYY. Watlington called the move a "proactive measure" to prevent the spread of illnesses.

The decision mirrors how the school year began, with two weeks of masking that began in August.

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Of the three illnesses. Only RSV -- respiratory syncytial virus – lacks any kind of vaccine. RSV is a fairly common ailment that normally results in cold symptoms, but it can be particularly dangerous for very young children and the elderly. Cases of RSV have spiked recently. According to an article published by NYU Langone, this could be the result of people dropping COVID-19 practices of masking and social distancing, as well as children who did not catch it during the COVID pandemic now being exposed to it.

In Boston, some parents want schools to bring back school mask mandates when students return after winter break.

The organization  BPS Families for COVID Safety wants 10 days of masking and increased COVID-19 testing. They presented a petition to school headquarters Wednesday with almost 200 signatures, according to NBC Boston. Boston Public Schools has not made any decision yet.

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"Student safety is paramount at Boston Public Schools. We continue to meet daily with the Boston Public Health Commission to review the latest BPS data and make informed decisions regarding our COVID-19 protocols," they said in a statement.

In California, Los Angeles County officials have stopped short of requiring masks for everyone, but they are recommending that everyone from the age of 2 and older wear masks indoors again. County Department of Health Director Dr. Barbara Ferrer said last week that millions of county residents are at elevated risk from the flu, RSV, and COVID-19 and advised masking up for several weeks.

"When you put on your mask for these few weeks during this surge, it's about the people of L.A. County," Ferrer said.

While the county is not requiring masks, a future mandate has not been ruled out, but it also is not being viewed as an inevitability.

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"We're actually not sure that we'll get there," Ferrer said.

The county does require masks for people who have COVID-19, as well as for those who have been in close contact with people who have it and those who work or live in places that had a recent outbreak. Mask mandates are also in effect in healthcare settings and congregate care facilities.

In Chicago, Department of Public Health commissioner Dr. Allison Arwady said she personally wears masks in public indoor settings, even though there is no mandate in place.

"I would advise putting a mask on, you know, while we're in high respiratory season. If you're in these crowded sites, you know, if you're on the L, and if it's busy, you know, in a store, etc.," she said, according to NBC Chicago. She noted that if hospitalization numbers climb, "we may make some more broad recommendations for [the] general population kind for indoor mask wearing, not requirements right at this point, but some more recommendations."

Chicago is located in Cook County, which the CDC lists as a "medium" community level of COVID infections. Of the state’s 102 counties, 12 are listed as "high" level, which means the CDC recommends that everyone wear masks, whether they are vaccinated or not.

New York City officials are also strongly recommending masks this winter. The city’s Department of Health issued an advisory last week urging residents to wear a mask in certain situations amid "high levels of COVID-19, flu and RSV."

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In a Friday press release, the New York City Department of Heath said that "high-quality masks" should be worn when "indoors and in crowded outdoor settings."

The advisory states that "everyone should wear a mask" when "in an indoor public setting, including inside stores, offices, lobbies, hallways, elevators, public transportation, schools, child care facilities, and other public shared spaces.

Nearby locations are taking varied approaches to masks. In New Jersey, for example, Gov. Phil Murphy is not requiring them.

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"I don’t foresee any mandates in New Jersey unless something drastically changes," Murphy said Monday, according to NJ.com.

Things are different at New York’s SUNY Purchase school, located in Westchester County, just outside New York City. The school’s website currently says that masks are "mandatory" indoors.

WHD News’ Julia Musto and Adam Sabes contributed to this report.