SANTA ROSA (KPIX 5) – As Sonoma County reported about 40 fully-vaccinated people had contracted COVID-19, health experts said it was not surprising and no cause for alarm.

As of Wednesday, the county in the North Bay has administered over 370,000 doses of COVID-19 vaccine. But, even with those numbers, 39 fully-vaccinated people in Sonoma County have contracted COVID-19.

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It’s called a “breakthrough case” when someone fully vaccinated, defined as two weeks after the final dose of vaccine, gets sick.

Dr. John Swartzberg of UC Berkeley puts it this way.

“With the vaccine, you have a coat of armor on, but we know that that armor is not completely protective. So you’ve got to consider yourself protected to a large extent, but you still could get infected. So, you want to be careful,” Swartzberg told KPIX 5.

Of those 39 breakthrough cases, only one was hospitalized and was released in 48 hours in Sonoma County.

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“The vast majority of people who get infected after they’ve been fully-vaccinated either don’t have symptoms or have very, very mild symptoms,” Swartzberg said.

Dr. Peter Chin-Hong at UCSF told KPIX 5, “It’s not surprising, in fact, we’re probably going to expect more than the numbers in Sonoma.”

Both Swartzberg and Chin-Hong said the 39 cases are statically in line with those numbers and that is likely happening throughout the state and nation as well.

“No vaccine protects 100 percent of the time,” said Swartzberg.

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Nationally, the Centers for Disease Control has been tracking so-called breakthrough cases and discovered 5,800 out of 66 million fully-vaccinated Americans.