A health official in a California county said socializing over Memorial Day weekend is likely behind a recent spike in cases of the novel coronavirus there.

At least 31 new cases of COVID-19 were reported in Napa County last week, twice the amount from the week before, and three times the amount of the week before that, the Napa Valley Register reported.

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Napa County’s Public Health Officer Dr. Karen Relucio told the outlet that graduation parties, gatherings with friends and family, and other social activities over Memorial Day weekend have contributed to the recent increase.

“Two weeks ago was Memorial Day. People were out and about. One case went to a graduation party with 40 people attending. Gatherings of that size are generally not allowed under the shelter-in-home order,” Relucio told the Napa Valley Register.

“We had another case go to church while they were symptomatic. We had another case who had their friends over even though they were symptomatic,” she continued.

“People are forgetting,” about the virus, especially as the state continues to see more non-essential businesses reopen.

“We don’t have community immunity to COVID-19. We don’t have a vaccine. It’s highly contagious,” she said.

Relucio warned that further reopenings could be in hot water if cases in the county continue to rise, as state health officials are monitoring counties that are seeing a spike in cases.

“Enjoy your summer, but keep your distance and [a] wear face covering. The physical distancing is so important to keep following,” she said, noting people should only socialize with members of their own household as much as possible.

The news comes after another California health official warned the state may be reopening too quickly.

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Dr. Sara Cody, health officer for Santa Clara County who issued the country's first shelter-in-place order, said last month that she was troubled by the state now allowing gatherings of 100 people for various purposes and noted that the pace at which the state is reopening at large is “concerning.”

“The state has shifted away from the stay-at-home model and has made significant modifications with increasing frequency,” since the beginning of May, Cody said at the time.