BERKELEY (KPIX 5) — First it was the San Jose Sharks.  Now, the UC Berkeley football team is dealing with multiple breakthrough cases of COVID-19.

A Cal football team spokesperson said multiple players are in COVID-19 protocols. The team declined to say how many people tested positive, but said 99% of the players on the Golden Bears squad are fully vaccinated.

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They’re not alone.

“Got to plow ahead.  I mean, we’re down a bunch of people and that’s the reality of this COVID world right now,” said Sharks player Logan Couture on Friday after practice.

As of Friday afternoon, seven San Jose Sharks continue to be sidelined and on the COVID list. Head coach Bob Boughner and two other staff members are also out due to COVID-19. The team said it’s 100% vaccinated.

“The breakthrough cases are not surprising to me,” said UCSF infectious disease expert Dr. Peter Chin-Hong, who does not work with the two teams or infected players directly.

Chin-Hong said vaccine efficacy fades with time. The doctor suspected that could be one possible explanation for the breakthrough cases on the Cal football and Sharks teams.

“When you’re sharing locker rooms, and in close contact and eating together, I think it’s easy to transmit an infection to other individuals with waning immunity,” Chin-Hong told KPIX 5.

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A new study published in the journal Science on Thursday showed all three major vaccines lose power over time.

Bay Area researchers from Oakland and San Francisco tracked about 500,000 vaccinated U.S. Army veterans.

They found Moderna measured 89% effective in March, but it went down to 58% effective by the end of September. Pfizer fell from 87% to 45% in the same period.

Meanwhile, the Johnson and Johnson vaccine plunged from 86% down to 13% after six months.

Despite the decline, the study finds the vaccines are still highly effective in preventing COVID-19 deaths.

“Individuals who’ve been vaccinated have a very, very, very low probability of getting very ill and going to the hospital,” said Dr. Chin-Hong.

The doctor said with the Sharks and Cal football breakthrough cases, it’s a reminder for the public to get a booster. Doesn’t matter your age, he said if you live or work in high-risk settings, you’re qualified to get the booster shot.

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A Cal spokesman said football players who tested negative boarded a flight to Arizona earlier Friday afternoon. Since they declined to provide details and the number of infected players, we should be able to find out in Saturday’s game how many players are affected.