SAN RAFAEL (KPIX) — Just as mask mandates in the Bay Area begin are lifting, now there is a rise in cases that elevates the entire Bay Area into CDC’s substantial and high transmission tiers. But that doesn’t mean some counties will reimpose mask mandates to slow the spread.

On Monday, Marin County rolled back its indoor mask mandate for those that are vaccinated. The county says cases have gone up but not high enough to change the rules again.

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Marin County Public Information Officer Laine Hendrick says it wasn’t a surprise that the county fell back in the substantial tier for transmission.

Hendrick adds, “What happened today was a couple of extra cases in the last couple of days is all it took for us to be above that threshold of orange. So for a county that’s on that margin, we sort of expected there to be a little dance between yellow and orange.”

But mandating everyone to mask again is being put on hold since hospitalizations remain low and more than 80% of the population is fully vaccinated.

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The Bay Area as a whole though is seeing an increase in cases and it has some in the medical field concerned.

“There’s transmission going on and this is a result of not having a number of sufficient people vaccinated,” says UCSF epidemiologist Dr. George Rutherford.

Dr. Rutherford fears with the holidays coming up, the Bay Area could see a sustained increase in cases. He says the next few weeks should focus on 5-11 year olds, boosters and increasing the number of those vaccinated with mandates.

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“If we’re running around with lots of 20-40 year old unvaccinated, we’re going to have problems,” he says.