SAN FRANCISCO – It may not take true ‘herd immunity’ to see a dramatic drop in COVID-19 cases. Some researchers estimate that 30 to 40 million additional first vaccines could be enough in the United States to reach a vaccine tipping point and stem the disease caused by the coronavirus.
“It’s just 10-15% more people,” said Dr. Eric Topol, professor of molecular medicine at the Scripps Research Institute in La Jolla, Calif.
So far, 44% of the U.S. population has received at least one vaccine and 31% are fully vaccinated, according to the Centers for Disease Control and Prevention. A tipping point occurs when enough people are vaccinated for COVID-19 cases to begin to drop dramatically and the spread of the virus to be contained – not stopped, but slowed enough to prevent large outbreaks.
“When you’re at around 50%, you put significant downward pressure on cases. Half of those potentially exposed to the virus can no longer catch it. It’s a really big deal,” Dr Robert said. Wachter, professor and director of the department of medicine at the University of California at San Francisco.
Topol pointed to California, which has so far vaccinated 50% of its people, as the model for what even slightly higher vaccination levels can mean. The 7-day average case rate in the state is only 4.3 cases per 100,000 people. This is down from 5.5 per 100,000 a month ago and 9.6 per 100,000 for the last week of February.
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“We are seeing the first clue of it here,” he said. “It is the largest state (in terms of population) and it has never looked better since day one of the pandemic.”
In San Francisco, where 72% of people aged 16 and over received at least one dose of the vaccine, only six people died from COVID-19 during the entire month of April. It is in a county of 882,000 inhabitants.
“These numbers are dropping dramatically – quintupled in terms of death rates,” said Dr. Grant Colfax, director of the San Francisco Department of Public Health.
He attributes this to the city’s emphasis on public health measures to reduce transmission and community-based vaccination campaigns.
“We have built an ‘every door is the right door’ approach to immunization,” said Colfax.
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While cases are increasing in some states, they are decreasing nationally. Perhaps more importantly, they are falling like a stone in the highly vaccinated age groups. Among Americans aged 65 and older, who are most vulnerable to the disease, two-thirds are fully immunized.
They were 94% less likely to be hospitalized with COVID-19 than people the same age who weren’t vaccinated, a CDC report showed last week.
These trends continue to decline in the population as more people get vaccinated, said Michael Pieciak, commissioner of the Vermont Department of Financial Regulation, responsible for the state’s COVID modeling and data. Vermont has the third highest vaccination rate in the country at 56%.
“COVID case rates are down 60% during the month of April,” Pieciak said, even among younger and less vaccinated people.
Although better weather conditions allow more outdoor activities may be a factor, he believes vaccination has played an important role.
“We almost hit that 50% mark in mid-April,” Pieciak said. Even though this (younger) group is not yet well covered, the rest of the Vermont population had good coverage and it had an effect. “
The UK reached its tipping point when around 50% of its residents received their first dose, said Dr Monica Gandhi, an infectious disease physician at the University of California, San Francisco. Cases there have fallen by 10% and deaths by 31% last week.
In Israel, which at 60% has one of the highest vaccination rates in the world, COVID-19 cases are less than 1 in 100,000.
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Gandhi is working with disease modellers who predict COVID-19 cases in the United States could drop to 10,000 a day on May 29 or even earlier. Currently, the country registers 48,000 cases per day – the first time since October, the daily count has fallen below 50,000 and 17% lower than the week before.
Getting an additional 30-40 million Americans vaccinated will require community-based approaches, positive motivational messages for vaccine uptake, and a lot of education, but Gandhi believes it’s possible.
“I’m almost convinced that we can get 60% of adults to agree to the vaccination – how sealed off seems to be,” she said.
Topol added, “It doesn’t matter who gets the vaccine. We just need to find 40 million more people to do it.
However, not everyone is convinced of the number vaccinations needed is quite low.
Dr Paul Offit, director of the Vaccine Education Center and infectious disease specialist at Children’s Hospital in Philadelphia, believes to bring COVID-19 under control closer to 80% of the population’s need for immunity.
Between vaccinations and natural immunity against previous infections, it currently places the United States at about 50% population immunity.
He attributes the current decrease in cases nationwide to a combination of vaccination, immunity through infection and a natural decline of the virus in the spring and summer.
“COVID-19 is at the heart of a winter virus,” Offit said.
If its numbers are correct, the nation still needs a large chunk of the population to roll up its sleeves.
“You need to vaccinate an additional 100 million people before next winter,” he said.
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Israel is having success with lower overall immunization levels because Israelis behave differently, Offit said.
“They have vaccination passports, so you can go to a place where you know other people are vaccinated. They think like a society, but we think as a group of individuals, ”he said.
Others point out that reaching a tipping point where cases drop dramatically is not the same as gaining collective immunity, which gives a population broad protection against the disease. It is estimated that herd immunity to COVID-19 requires between 80% and 90% of people protected by vaccination or previous infection.
“I have the impression that many places will have a lot of vaccinated and that there will be other places where, for political reasons or for many others, choose not to be vaccinated. So while the overall numbers will definitely go down, I’m worried about the surges, ”said Barry Bloom, immunologist and global health expert at Harvard TH Chan School of Public Health.
In Westchester County, New York, where 52% of people have received at least one dose of the vaccine, the number of COVID-19 cases, hospitalizations and deaths are on the decline, said Dr Dial Hewlett, county medical director of the disease control division.
He worries as COVID-19 rates decline, those who are not vaccinated will feel less pressure to sign up for a vaccine.
“It’s like when you have a big forest fire and you are able to contain just about all the fire, but there are embers smoldering,” he says. “We don’t want to let our guard down and become complacent.”
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