High Bay Area Vaccination Rates Likely to Tamp Down Future COVID-19 Outbreaks

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A nurse gives a COVID-19 vaccine shot to a patient at the Cal State Northridge COVID-19 vaccination center in Northridge, Calif., on Feb. 2, 2021.  (Valarie Macon/AFP via Getty Images)

The Bay Area continues to outpace most of the country in terms of vaccination rates. Other key contenders include the state of Vermont and the city of Seattle.

Marin County is leading the nine Bay Area counties with 78% of all residents at least partially vaccinated. San Francisco is next in line with 72%. 

Vaccine rates in the other local counties hover in the high 60s. Solano County is at the back of the pack with 64% of eligible residents vaccinated, which is on par with Los Angeles County’s vaccine rate. 

When a majority of people are immune to COVID-19, either through a vaccine or because they have caught the bug, the virus can no longer spread because it runs out of vulnerable people to infect.

Epidemiologists predict these conditions for COVID-19 will occur when 75% to 85% of a population is protected. 

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“We are closing in on herd immunity,” said UCSF epidemiologist Dr. George Rutherford. “It is very exciting. Very gratifying. It’s a miracle of modern molecular biology.”

However, herd immunity is not a finish line because it’s impermanent. There are many factors at play. The virus can still mutate and kids under 12 have not received their shots yet. Plus scientists are just guessing at this point because they do not know what level of vaccination will actually keep the virus at bay. 

But Rutherford says he is not worried about potential outbreaks following the state’s reopening on June 15. Small clusters of illness may arise but, he says, they are not likely to ignite substantial transmission. The virus can no longer spread rapidly within the community because a majority of the population is protected. The surges the Bay Area experienced when restrictions were lifted in the past are highly unlikely this time around. 

Officials at the San Francisco Department of Public Health are encouraged by local numbers, but also stress the delicacy of the situation. “There are some populations that continue to be susceptible to the virus, including communities that have lower vaccination rates as well as those people who are ineligible for vaccines, such as children below 12 years of age,” a spokesperson wrote in an email. “New variants are emerging, and the pace of vaccinations varies across the world.”

Although current data is encouraging, scientists do not know if a vaccinated person can transmit the virus, and doctors do not know how long immunity to the virus lasts. Plus, we live in a highly global society connected by roads, trains and international airports. 

“Herd immunity is really a term that's designed for closed populations,” said Stanford epidemiologist Julie Parsonnet. “We are not a closed population by any stretch of the imagination. Until the world has immunity, then no one really has an immunity.”

Parsonnet worries that focusing on the idea of herd immunity could send the wrong message to the public — especially when some people are still hesitant about getting a shot. They may interpret high vaccination rates as a sign that getting vaccinated is no longer necessary. 

“And that's not really the truth,” she said. “I think there are a lot of things that can still go wrong. We can't predict the future and we need to prepare for it by using the tools that we have as aggressively as we can.” 

In other words, high vaccination rates alone are not a panacea to stamp out the pandemic. Contact tracing and testing will still be required to quell small outbreaks going forward. 

Parsonnet underlines that it took about 40-years to reach herd immunity for measles and doctors only had to vaccinate children to stop that virus. Every time someone is vaccinated it prevents further cases and potentially saves lives. The only way to truly stop COVID-19 is one shot at a time.