By Stephanie Stahl

PHILADELPHIA (CBS) — Health officials are concerned there could be a spike of COVID-19 cases following the holiday weekend. That’s because there were some clusters of people not following the recommendations to social distance or wear masks.

After months of sheltering in place, millions of Americans ventured out for the holiday weekend, with restrictions eased in all 50 states.

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Doctors are worried about people who were in crowds, unprotected, potentially putting themselves and others in danger.

“I have to admit, Mother Nature helped because the weather was God awful,” New Jersey Gov. Phil Murphy said.

He also says the weather helped keep the crowds down for the holiday weekend. But there were clusters on the boardwalk in Wildwood not keeping a safe distance or wearing masks.

“This corona will not stop us, I’m here to have fun with friends,” one person said.

It was a scene repeated around the country. A crowded pool party at Lake of the Ozarks prompted health officials in Missouri to issue a travel advisory for people at the party to self-quarantine for two weeks.

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“I would express concern about those individuals as we’ve been saying there is still community spread of COVID-19,” Pennsylvania Health Secretary Dr. Rachel Levine said.

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“Wearing a mask has to become the normal expected behavior of what we do when we’re around other people. That’s the way we can restart our economy safely. So if you haven’t done it yet, get a mask and get used to wearing it,” Philadelphia Health Commissioner Dr. Thomas Farley said.

Twenty-five states reported increases in new COVID-19 cases compared to two weeks ago.

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Pennsylvania, New Jersey and Delaware are steady, but Philadelphia Mayor Jim Kenney is worried if people don’t take precautions, the Philadelphia region could see an increase in cases.

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“We have to continue to talk to people and make sure that they understand that every time they do something irresponsible, they’re putting themselves and their families in jeopardy,” Kenney said.

While COVID-19 is most dangerous to the elderly, doctors say it also strikes young people — they’re not immune.

And while the coronavirus might transmit less efficiently in the summer, that doesn’t mean it will go away.

Stephanie Stahl