What are the chances of getting a breakthrough case in San Francisco?

The New York Times estimated in its Tuesday newsletter that your chance of getting a breakthrough case — that is, catching COVID-19 if you’re vaccinated — in San Francisco is about 1 in 10,000.

San Francisco is a well-vaccinated city with 80% of residents 12 and older completing a vaccine series. Experts said the probability of a breakthrough case in S.F. is lower than in other parts of the country where vaccine rates are lower and where the virus is circulating more widely.  

This estimate was extrapolated from new data providing a more clear picture of the impact from the delta variant, the most common COVID-19 strain in the U.S.

Using detailed data on infections by vaccination status from Utah, Virginia and King County in Washington state, the Times found that in these places, one in 5,000 vaccinated people tested positive for COVID each day in recent weeks. 

“The chances are surely higher in the places with the worst Covid outbreaks, like the Southeast,” the Times said. “And in places with many fewer cases — like the Northeast, as well as the Chicago, Los Angeles and San Francisco areas — the chances are lower, probably less than 1 in 10,000.”

Dr. Monica Gandhi, an infectious disease expert at UCSF, agreed the chances in San Francisco are lower. 

“Given our decreasing cases in the city, I think the rate is likely less than 1 in 10,000 now in the city of San Francisco,” Gandhi wrote in an email. “I don’t know what it is exactly and essential workers and those in crowded living environments likely have a higher chance of a breakthrough.”

She also said the probability is probably about the same across the nine-county Bay Area. 

To put that in perspective, Gandhi noted the chance of getting a breakthrough case is likely the same as confronting rhinovirus, RSV or other common cold viruses that are circulating at higher rates this year, according the Centers for Disease Control and Prevention (and circulating earlier than usual).

The chances of getting a breakthrough case in the San Francisco Bay Area are less than in other parts of the country where vaccine rates are lower and where the virus is circulating more widely.  

“Our numbers (test positivity specifically) [are] decreasing across the Bay Area,” Gandhi wrote.

Dr. Ashish Jha, a dean and professor at the Brown University School of Public Health, commented on the Times article on Twitter and wrote that he thinks in lower infection states such as Massachusetts or Rhode Island, the risk is “probably closer to 1 in 20,000.”

California has recorded 124.3 new cases per 100,000 in the last seven days, while Massachusetts has seen 108.7 and Rhode Island 133.8, according to the CDC’s data tracker.

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