SAN FRANCISCO (KPIX) — Even as California continues to reopen, public health officials are warning about the so-called Delta variant and the threat it poses to the unvaccinated.

“The variants are just getting more and more powerful. It’s just going in the wrong direction,” says Dr. Peter Chin Hong, an infectious disease expert with UCSF. “And the reason why is because of the virus is mutating. Every two weeks, it’s making a mutation that could potentially be even worse than the last one.”

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Researchers estimate the Delta variant may be 50% more contagious than the UK strain of the virus. There’s also emerging evidence that it may result in more severe illness.

Pfizer says its vaccine is only 33% effective against the variant for partially vaccinated individuals — people who have only received their first dose of the vaccine.

“We can’t take any chances I feel like as far as that goes,” says parent Jennifer Johnson.

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Even with the state of California reopening, Jennifer Johnson says her family remains on lockdown until her two young children are fully vaccinated.

“I want to travel again with my family. I want to go and do things just like pre-pandemic. But we’re limited still because those variants are scarier and more transmissible,” Johnson said.

Public health officials in Santa Clara County are focusing their vaccination efforts on teenagers. They held a raffle for recently vaccinated teens with prizes ranging from tickets to upcoming Bad Bunny, Harry Styles and Enrique Iglesias concerts.

The vaccination rate among young people aged 12 to 17 in Santa Clara County is 58%, compared to 81% overall.

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“There’s still a lot of people out there who are vaccinated. And we’re in a race against those variants. And testing has found all of those variants in our county,” says Dr. Marty Fenstersheib.