The rise in COVID-19 is now serving to to create herd immunity

With coronavirus cases falling across the country and vaccinations spanning 1.7 million Americans daily and increasing, health experts are increasingly picking a new tone in their pandemic assessments: optimism.

“I might be wrong, but I don’t think we’re going to see a big fourth climb,” said Dr. Paul Offit, a vaccines expert at Philadelphia Children’s Hospital. “I think we saw the worst.”

Many epidemiologists and other scientists, while still cautious, are increasingly hoping that the rest of 2021 will not repeat last year’s nightmare.

The arrival of spring is likely to aid the ongoing steep decline in coronavirus cases as warmer weather allows people to spend more time outdoors and creates a less hospitable environment for the virus, experts say.

But the biggest factor, paradoxically, is something the nation has tried to prevent over the past year.

While 12% of Americans have received at least one dose of the COVID-19 vaccine, Offit estimates far more people – about 35% of the country’s population – are already infected with the coronavirus. Studies have shown that people who survive COVID-19 have immunity for several months, although it is likely to last longer.

UC San Francisco epidemiologist Dr. George Rutherford said one of the reasons cases are falling so rapidly in California is “naturally acquired immunity, mainly in Southern California”. He estimated that 50% of Los Angeles County’s residents were infected with the virus at some point.

“We’re really talking about what is starting to sound like what herd immunity looks like – although that true herd immunity is still a long way off in the future,” Rutherford said recently.

Herd immunity is achieved when so many people have immunity that a virus cannot find new hosts and cannot spread, resulting in community-wide protection. Scientists believe that in the case of the coronavirus, the threshold could be up to 90%. The United States has not reached that threshold, but every step in that direction is slowing down transmission, experts say.

The impact can be greatest in locations that have seen the worst COVID-19 hits, including Los Angeles. After a terrible fall and winter wave that killed more than 12,000 people, an estimated 33% to 55% of the county’s residents are already infected with the coronavirus, according to USC researchers.

These earlier infections slowed coronavirus transmission so much that they changed the current course of the outbreak in LA County, which has seen new daily cases for the past five weeks, said Dr. Roger Lewis, director of COVID-19 hospital demand modeling for the LA County Department of Health Services.

“If you had exactly the same behavior and type of virus that we have floating around right now, but we were at the beginning of the pandemic and no one was immune yet … we would be in the middle of an ongoing wave.” he said. “The fact that cases are now falling, not rising, is because roughly a third of all people in Los Angeles County are immune to COVID.”

However, experts warn that the battle is not yet won.

New coronavirus variants could undermine these predictions by either proving more resistant to existing vaccines or finding a way to spread more easily. Behavioral changes could also call this good news into question, as it only applies if people stick to the precautions they have taken so far, experts say.

“I don’t want to give a false sense of certainty here,” said Dr. Paul Simon, LA County’s chief science officer, who pointed out that 60% of Angelenos would remain vulnerable even if more than a third had already been infected with the coronavirus. “If they haven’t been vaccinated, they are still vulnerable. I think we must continue to be vigilant. “

Nationwide, the cases of corona viruses have fallen to a level not seen since the end of October, according to federal officials. In California, approximately 7,000 people test positive for the coronavirus every day, compared to 45,000 at the height of the state’s winter flood.

LA County officials currently estimate the R-value – a measure of how many people a person has infected with the virus – at around 0.8. Anything below 1 means an outbreak is shrinking and anything above 1 means it is growing.

If that many people in the county weren’t already immune, the R-value would be about a third higher or just over 1, Lewis said. Even this slight increase has significant ramifications for a virus that is spreading exponentially.

“The fact that the virus only has two-thirds as many people to jump to as it did early is slowing it down,” Lewis said.

Since the pandemic started, nearly 30 million Americans have tested positive for the coronavirus, but the real number of those who contracted the virus is likely three or four times higher because few tests have been done and many infected people never develop symptoms , Experts say.

The large number of infections is associated with high costs. The nation’s death toll is nearing 500,000, far more than any other country in the world, and even more have survived but continue to suffer from the ongoing effects of their diseases, some of which are severe. According to experts, it would have resulted in even more deaths and chronic health problems if COVID-19 had been widespread to quickly achieve herd immunity, as some promoted at the start of the pandemic.

It remains unclear exactly what the herd immunity threshold is for this virus. Some scientists estimate that herd immunity can be achieved when 50% of people are immune, while others believe the threshold is closer to 90%, said Simon of LA County. The uneven geographic distribution of infections could also make some areas of the county more vulnerable than others, he said.

“We don’t yet know exactly what level of vaccination and protection is required to achieve herd immunity across the county,” Simon said in a briefing on Friday. “As we can see, the number of new cases is falling dramatically – this is the best indicator in my opinion that we are reaching herd immunity, especially when we see this across the county.”

The biggest obstacle to ending the pandemic is the spread of coronavirus variants.
especially if they are more transmissible or less susceptible to vaccines. For example, variant B.1.1.7 developed in the UK is about 50% more contagious than its predecessors and could trigger outbreaks in locations where large swaths of people remain susceptible to disease.

Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, said he believes flying to visit friends and family will be normal and safe by August. But because of the variations, he warned people “Beware of March’s Ideas”.

“I think this is the biggest crisis we are currently facing in our COVID-19 pandemic,” he said in a recent interview with the American Medical Assn. “As bad as 2020 was, now let’s look at version 2.0 of this pandemic from the variants.”

Others, however, are more optimistic. Offit said he was concerned if people who had already had COVID-19 or had been vaccinated would be hospitalized for infections caused by a new variant.

“That limit was not exceeded,” he said. “They just want to keep people out of the hospital, and it looks like to date there hasn’t been a variant that has evaded the immunity caused by illness or vaccine.”

At a COVID seminar held by the UCSF Department of Medicine last week, Dr. Monica Gandhi, an infectious disease specialist, simply: “Don’t worry about the variants.”

Offit said he continues to hope for the nation’s development over the summer and for more people to be vaccinated. “What worries me a little is if you get to September and then it gets colder again and a variant might show up,” and people stop wearing masks and distancing themselves physically, Offit said.

Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, cautioned against viewing declining case trends as a reason to ditch masking and other safety precautions.

In an interview with the Journal of the American Medical Assn. Walensky said she hopes for the best but also warns of a worst-case scenario – that people stop wearing masks and distance themselves too soon, and that many are declaring ahead of time that they’ve had enough of the pandemic and will not be vaccinated.

“How that works will depend on 330 million people,” said Walensky. “Because while I’m really hopeful of what could happen in March and April, I really know this could go bad – so quickly. And we saw it in November. We saw it in December. We saw what can happen. “

Dr. Annabelle de St. Maurice, a pediatric infectious disease specialist at UCLA, said she sympathizes with officials trying to draw the fine line between maintaining morale and feeling that people don’t feel as optimistic that they do lead their guard downstairs.

In LA in particular, the numbers have improved dramatically, but they remain almost as high as they were during the deadly Summer Flood.

“It’s cause for celebration and you want people to celebrate, but you want them to be physically aloof while wearing a mask,” she said.

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