Breakthrough cases account for 17 percent of county’s COVID surge

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One hundred and forty of the 798 new COVID-19 cases reported in Yolo County between June 1 and July 25 were among fully vaccinated individuals, in line with what Health Officer Dr. Aimee Sisson predicted several weeks ago. Sisson had said with vaccines that are 80 percent effective against the Delta variant and about half of the county’s population fully vaccinated, she would expect 17 percent of cases to occur in vaccinated individuals. Between June 1 and July 25, it was 17.5 percent. That percentage, Sisson said, will increase as the percentage of vaccinated residents also increases. The rate of breakthrough cases in Davis, which has a high level of vaccination, may be nearly twice as high, according to Healthy Davis Together, which reported Friday that between 25 percent and 33 percent of all new cases are in fully vaccinated individuals. But the bottom line, health officials with both the county and Healthy Davis Together said, is that while the COVID-19 vaccines may not provide complete protection from infection, they do provide overwhelming protection against hospitalization and death from the virus. In fact, data from a Centers for Disease Control and Prevention report released Friday show just how much. While the weekly case rate among the nation’s unvaccinated population is 178.6 per 100,000 residents, it is 21.4 for the vaccinated. The difference is greater with hospitalizations and deaths. The incidence of hospitalization among the unvaccinated is 2.52 per 100,000, compared to 0.1 among the vaccinated. Likewise, the weekly rate of deaths among the unvaccinated is 0.96 per 100,000 people, versus 0.04 among the vaccinated. Breakthrough cases among the vaccinated were always expected with vaccines that do not provide complete protection against infection. What was new last week was health officials, including Sisson, reporting that vaccinated individuals who do become infected with the Delta variant can transmit the virus to others. That, in turn, prompted the CDC to recommend that everyone resume wearing masks in indoor public places where virus transmission is substantial or high. Sisson took the recommendation a step further, mandating masks for everyone over the age of two in Yolo County, effective Friday. She and others also continue to plead with county residents to get vaccinated. “We are at a critical moment that calls for increased caution and care for the health of our communities,” said Dr. Sheri Belafsky, medical director for Healthy Davis Together. “This includes getting vaccinated as soon as possible, getting tested regularly and following local mask guidance.” Of course not everyone can get vaccinated. Children under 12, in particular, remain largely unprotected from the virus. According to county data shared by Yolo County Supervisor Don Saylor on Thursday, children under 12 accounted for 95 of the 798 new COVID-19 cases reported in the county between June 1 and July 25. No age group of unvaccinated county residents had more cases during that period and 11 of those children were infants under the age of one, something Saylor called “disturbing.” Unvaccinated individuals continue to make up the bulk of new cases in Yolo County — at least 404 of the 798 cases between June 1 and July 25. Vaccination status for another 254 positive cases was unknown. New COVID-19 cases among the unvaccinated were spread across all age groups. While children under 12 accounted for the most cases, other unvaccinated age groups with more than 50 cases included those ages 20 to 24 (51 cases) and 35 to 44 (58 cases). Among fully vaccinated residents of the county, the age group with the most breakthrough cases was 35 to 44, with 27 cases between June 1 and July 25. There were six breakthrough cases in individuals over age 75. Among all residents — vaccinated, unvaccinated and vaccine status unknown — the 35 to 44 age group accounted for just over 15 percent of new cases, the most of any age group. Those 20 to 24 accounted for 14.7 percent and those 25 to 29 accounted for 12.7 percent. New cases have continued to surge since that data was collected. Over the past seven days, the county has reported 348 new cases of COVID-19, up from 276 the week before and 170 the week before that. Healthy Davis Together reported last Friday that test positivity rates in and around Davis are at the highest point since January and the Delta variant is a key reason why. Every positive test sample collected by Healthy Davis Together through its local testing program, as well as those collected on campus, are sequenced by the UC Davis Genome Center to check for variants. Between July 18 and July 24, the Genome Center identified 117 cases of the Delta variant among the 120 positive cases found. Those 111 cases were nearly three times the number of Delta variants identified the week prior. Unsurprisingly, the CDC in the report released last Friday, said, “the war has changed” when it comes to battling COVID-19. The Delta variant is so contagious, the report said, that it is transmitted as easily as the chicken pox and may be as easily transmitted by vaccinated individuals as by the unvaccinated. Now, more than ever, the report stated, communication is key, particularly around breakthrough cases which are expected and will increase as vaccine coverage increases. Vaccines remain the best defense against COVID-19, as those with breakthrough cases generally have mild or no symptoms and hospitalizations and deaths are so rare.

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