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San Francisco is approaching herd immunity against COVID-19; LA is not

According to some experts, San Francisco is approaching herd immunity, a cornerstone in California’s efforts to control the COVID-19 pandemic.

San Francisco has one of the highest levels of vaccination in California, with 72% of residents receiving at least one dose. Only one other county in California – Marin, north of San Francisco – has a higher vaccination rate, with 75% of the population there being at least partially vaccinated. The percentage of both San Francisco and Marin County is significantly higher than the nationwide vaccination rate of 56%.

Herd immunity, also known as community immunity, is a form of indirect protection of people without immunity against disease from infection. This occurs when a significant percentage of the general population is immunized either by vaccines or by surviving a previous infection.

There is no definite percentage at which herd immunity to COVID-1

9 is achieved. It can only be tested when essentially all restrictions have been relaxed and staff are monitoring whether the transmission of the disease is increasing.

Previous assumptions about when a herd’s immunity against COVID-19 is achieved are between 70% and 85% of the immune community, either through immunization or through disease survival. Despite the vague parameters around reaching herd immunity, approaching it by increasing vaccination remains a top goal for public health experts.

“I think San Francisco is pretty close,” said Dr. George Rutherford, an epidemiologist at the University of San Francisco, who believes a good hypothesis for a threshold for herd immunity is north of 75 percent. “I think we’re in really good shape here, considering the city [of San Francisco]. Elsewhere we are very close. “

San Diego, Santa Clara and San Mateo counties also have some of the highest vaccination rates in the state, with nearly 70% of their residents vaccinated with at least one dose.

Other counties in or near the Gulf also have the highest vaccination rates in the state. In Alameda County, home of Auckland, 67% of residents have at least one dose of vaccine; in Napa County it is 66%; Contra Costa County, 65%; Santa Cruz County, 64%; and Sonoma County, 63%.

In contrast, Orange and Ventura counties have 57% of their inhabitants at least partially vaccinated; LA County, 55%; Sacramento County, 51%; Riverside County, 45%; San Bernardino County, 41%; and Kern County, 38%.

Los Angeles County Public Health Director Barbara Ferrer said she still doesn’t believe Los Angeles County has achieved herd immunity; she hopes to reach the end of the summer.

“We have a lot of people who haven’t been vaccinated yet,” Ferrer said. Achieving herd immunity would mean that the daily rate of coronavirus cases would have dropped so low that “you have great protection just because we have so many people vaccinated.”

Nothing suddenly happens when immunity to the herd is achieved – daily coronavirus levels in San Francisco are already at extremely low levels. And technically, herd immunity is achieved gradually: The more people gain immunity, the slower the rate of disease transmission.

But once the herd’s immunity is achieved, as new cases of coronavirus appear among unvaccinated people, for example through travelers, “they are very unlikely to reproduce for more than a generation or something like that. So you will not see these extended transmission chains, ”assuming that unvaccinated people are randomly distributed among the population and not all come together.

Some experts have expressed confidence that California will not give in to a worse phase of the pandemic after June 15, when the country is set to fully open its economy and remove the lion’s share of business restrictions aimed at curbing the spread of coronavirus that persisted, in the counties of California in the smallest restriction, indoor restaurants and gyms at 50% of indoor capacity.

“We’ll see on June 15 if we stay low on cases – I have no doubt we will,” said Dr. Monica Gandhi, an infectious disease specialist in San Francisco.

California already has extremely low levels of COVID-19 hospitalization – there are about 1,000 people in the state’s hospitals with COVID-19, up from 22,000 in January. The latest figures are the hospitalization rate of about 2.6 Californians hospitalized with COVID-19 per 100,000 population, compared with a peak of 56 per 100,000 population.

The latter number is significant, as Gandhi suggested in April that a good time when restrictions such as disguise and social distancing could be eased was when the number of hospitalizations fell below 5 per 100,000 inhabitants. During the peak of the flu season, the frequency of hospitalizations for influenza reaches a maximum of about 20 to 40 per 100,000 inhabitants.

Other countries with the fastest per capita vaccine administrations are showing promising patterns. Israel has recently lifted rules that restrict unvaccinated people from entering certain places, Gandhi said.

On Tuesday, federal officials expressed concern about the rise of the Delta variant, also known as B.1.617.2, which was originally identified in India and has spread to 60 countries, including the United States and the United Kingdom.

Dr Anthony Fauci, the government’s top infectious disease expert, said the Delta variant was more portable than the Alpha variant, also known as B.1.1.7, which was originally identified in the UK and has since become dominant in the United States “It may be associated with an increased severity of the disease, such as a risk of hospitalization, compared to alpha,” he said.

But fortunately, studies show that two doses of Pfizer and AstraZeneca vaccines provide sufficient immunity to protect against Delta variant infection, Fauzi said. AstraZeneca’s COVID-19 vaccine is not approved for use in the United States, but is similar to that produced by Johnson & Johnson.

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