Herd immunity in the United States? San Francisco offers reasons for optimism – fr

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Herd immunity in the United States? San Francisco offers reasons for optimism – fr


SAN FRANCISCO – Adam Bergeron is eager to reopen the Balboa Theater, the independent San Francisco theater he owns and operates.

He has seen other theaters in the United States welcome audiences before his own. But San Francisco has been slower to reopen than other cities. Now the time has come.

“San Francisco has been a model for doing Covid the right way, if there is such a thing,” Bergeron said.

“At this point, everyone I know is fully vaccinated. The cases are decreasing. And we just picked a time that seemed like the right time, ”he added. It plans to reopen on May 14 with a “Godzilla” marathon.

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San Francisco and its suburbs have been cautious, maintaining various restrictions while other parts of the country have reopened businesses and eased mask mandates. Meanwhile, its vaccination rate is among the highest of any major US city, with two-thirds of all adults having received at least one dose.

And as parts of the city open up – some bars in San Francisco have waiting lists to get a table again – experts are offering cautious optimism. The city may see signs of collective immunity.

“This is our time to put the pandemic behind us,” said Dr. Grant Colfax, San Francisco director of health. “It is clear that vaccines are our way out of this situation. “

Collective immunity concerns transmission. If enough people cannot catch and spread a virus, especially in a community that already has few cases, the virus is struggling to find new hosts. Eventually the infections would naturally decrease. It’s a simple concept, but it can be elusive and difficult to define – especially at the national level.

Locally, however, it can be clearer. Over the past seven days, San Francisco, home to more than 870,000 people, has averaged just 26 new cases of Covid-19 per day. Two-thirds of all adults in San Francisco and nearly 60% of the greater metropolitan area of ​​4.7 million people have been vaccinated with at least one dose – one of the highest rates in the United States. positive test rate is 1.2%.

Across San Francisco, there are signs of residents starting to relax their emergency precautions, at least slightly, and enjoy a reward from the vaccinations. Some people go maskless on outdoor walks – a rare sight until recently – while small gatherings like running and cycling clubs have resumed and studio yoga and other fitness classes have restarted. . Inviting a round of municipal applause, the main branch of the city library reopened Monday for navigation, and the city could enter California’s “yellow tier” this week – the least restrictive pandemic tier.

And there are signs the city is gearing up for a long-term reopening. Kevin Carroll, executive director of the Council of San Francisco hotel, a commercial group in the city’s hotel industry, said the majority of San Francisco’s 34,000 hotel rooms are expected to be open by the end of the year. May. Other downtown offices, including those of big tech companies, are coming back. Salesforce, the software company that occupies San Francisco’s tallest skyscraper, is aiming to reopen its headquarters this month, spokeswoman Annie Vincent said.

It is estimated that between 70% and 85% of a city’s population will need to be immunized to achieve collective immunity, but that number can be a moving target. A better indication is if a city’s number of cases and hospitalizations drops to low and low, even with few restrictions in place, said Dr Monica Gandhi, infectious disease physician and professor of medicine. at the University of California, San Francisco.

San Francisco had the advantage of stepping up its vaccination campaign when cases, hospitalizations and daily deaths were already relatively low, which is likely to explain much of the city’s success so far. Last winter, when much of the country struggled with a devastating outbreak, cases in San Francisco peaked on January 4 with 560 reported infections. By comparison, Los Angeles recorded its peak on December 26, with more than 29,000 new cases.

Vaccines can help lower those numbers, but how quickly this happens depends largely on the situation on the ground. In places where cases are increasing, scientists have observed an inflection point with vaccinations, after which cases, hospitalizations and deaths begin to drop dramatically.

“It appears to be at the first dose rate of 40 to 50 percent,” Gandhi said. “After that, things started to fall.”

There are currently 15 people hospitalized for Covid-19 in San Francisco, a figure that equates to roughly less than 2 per 100,000 people. While there is no magic number, Gandhi said it is these types of low hospitalization rates that public health officials monitor to make sure a city is on the right track.

In March 2020, San Francisco was the first city in the country to issue a mandatory shelter-in-place order in response to the pandemic. And the city has maintained other strict mitigation procedures which, according to Colfax, the San Francisco director of health, have helped the city “fend off three surges.”

Colfax also credited the widespread adoption of the city’s public health interventions for these advancements.

“This culture and support for public health and public health infrastructure runs deep in San Francisco, in large part thanks to our response to the HIV / AIDS epidemic,” he said. “It’s embedded in our cultural DNA. “

But the real test will likely come this week when the city begins to lift some of its restrictions.

“The final test when you get herd immunity is not to be locked out and not have mitigation procedures,” Gandhi said. “The way we could say that we came up with herd immunity to measles is that people were out and mingling and people weren’t getting sick and the kids weren’t hospitalized for one. severe measles.

Yet herd immunity is not a fixed target and the threshold can vary depending on a number of factors, including population dynamics. Getting herd immunity also doesn’t automatically guarantee that the coronavirus will simply go away. Even though more than 90 percent of the American population has received a measles vaccine, for example, there may still be outbreaks.

As such, herd immunity should not be seen as the end goal, said Dr Julie Parsonnet, professor of epidemiology and population health at Stanford University.

“It’s not something permanent, and just because we’ve achieved herd immunity doesn’t mean there won’t be a case,” Parsonnet said. “Collective immunity is a good construct for modeling, but not for life. “

There is also a risk that a variant of the virus could emerge that escapes the protection of vaccines. There is no evidence that this has happened so far, but if it did, it could undermine the protection communities have gained.

And while pockets across the country, like San Francisco, may have already achieved a level of immunity that allows most major restrictions to be lifted, it may take a long time for the whole country to get there – if ever. it happens. But that doesn’t mean lockdowns will last for years or that life can’t go on.

“If we get to the point where the coronavirus doesn’t make people very sick, we’ll be in good shape,” Parsonnet said. “If we fail to achieve collective immunity as a nation, we will still protect vulnerable people with vaccines and hopefully not suffer hospitalization. “

While San Francisco may be the first major American city to wrest control of the pandemic, others are probably not far behind.

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More than 46% of New Yorkers have received at least one dose of the vaccine, and cases, hospitalizations and deaths are all declining steadily. Los Angeles County, which less than five months ago was considered the epicenter of the pandemic in the United States, recorded no new deaths from Covid-19 on Sunday and Monday. Fifty-four percent of residents have received at least one dose of the vaccine, and that’s among several California counties ready to lift restrictions this week.

Elsewhere in the country, smaller towns like Albuquerque, New Mexico; Portland, Maine; and San Diego is making equally encouraging progress.

“It’s deeply encouraging,” Gandhi said. “Vaccines have brought us into an entirely new world. “

Denise Chow reported from New York City; David Ingram reported from San Francisco.



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