POST 96. December 26, 2020. CORONAVIRUS. “Achieving herd immunity against the coronavirus could require as much as 90 percent of the population to be vaccinated, Anthony Fauci…”…”..he hesitated to state a number as high as 90% weeks ago because many Americans still seemed skeptical about vaccine….”

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“Achieving herd immunity against the coronavirus could require as much as 90 percent of the population to be vaccinated, Anthony Fauci said in an interview published Thursday.

Fauci, the country’s top infectious diseases expert, acknowledged in the New York Times interview that he has been incrementally raising his estimate of herd immunity numbers.

Fauci said he has been increasing the estimates in his public pronouncements because he thinks Americans are now able to handle the message that getting back to normal may take longer than anticipated, and fewer Americans are reporting being skeptical of taking a vaccine.

“When polls said only about half of all Americans would take a vaccine, I was saying herd immunity would take 70 to 75 percent,” Fauci told the Times. “Then, when newer surveys said 60 percent or more would take it, I thought, ‘I can nudge this up a bit,’ so I went to 80, 85.”

The Times noted that about a month ago, Fauci began saying herd immunity would take “70, 75 percent” of Americans being vaccinated.

Last week, in an interview with CNBC News, Fauci estimated “between 75 and 80, 85 percent of the population.”

At that level of vaccination, Fauci said, “we would develop a umbrella of immunity. That would be able to protect, even the vulnerables, who have not been vaccinated, or those in which the vaccine has not been effective.”

Fauci said experts don’t really know for sure the level of vaccinations needed for herd immunity, but the initial estimates of 60 to 70 percent were based on early data.” (A)

“Dr. Fauci told The Times in an interview published Thursday that he had slowly but deliberately been moving the goal posts, partly based on new science, and partly on his gut feeling that the American public was ready to receive the information, which is that 70-90% herd immunity should be achieved before the country can go back to normal.

He said he hesitated to state a number as high as 90% weeks ago because many Americans still seemed skeptical about vaccine….

““We need to have some humility here,” he added. “We really don’t know what the real number is. I think the real range is somewhere between 70 to 90 percent. But, I’m not going to say 90 percent.”” (B)

“Asked about Dr. Fauci’s conclusions, prominent epidemiologists said that he might be proven right. The early range of 60 to 70 percent was almost undoubtedly too low, they said, and the virus is becoming more transmissible, so it will take greater herd immunity to stop it…

Measles is thought to be the world’s most contagious disease; it can linger in the air for hours or drift through vents to infect people in other rooms. In some studies of outbreaks in crowded military barracks and student dormitories, it has kept transmitting until more than 95 percent of all residents are infected.

Interviews with epidemiologists regarding the degree of herd immunity needed to defeat the coronavirus produced a range of estimates, some of which were in line with Dr. Fauci’s. They also came with a warning: All answers are merely “guesstimates.”

“You tell me what numbers to put in my equations, and I’ll give you the answer,” said Marc Lipsitch, an epidemiologist at Harvard’s T.H. Chan School of Public Health. “But you can’t tell me the numbers, because nobody knows them.”…

The original assumption that it would take 60 to 70 percent immunity to stop the disease was based on early data from China and Italy, health experts noted.

Epidemiologists watching how fast cases doubled in those outbreaks calculated that the virus’s reproduction number, or R0 — how many new victims each carrier infected — was about 3. So two out of three potential victims would have to become immune before each carrier infected fewer than one. When each carrier infects fewer than one new victim, the outbreak slowly dies out.

Two out of three is 66.7 percent, which established the range of 60 to 70 percent for herd immunity….

Further complicating matters, there is a growing consensus among scientists that the virus itself is becoming more transmissible. A variant “Italian strain” with the mutation known as D614G has spread much faster than the original Wuhan variant. A newly identified mutation, sometimes called N501Y, that may make the virus even more infectious has recently appeared in Britain, South Africa and elsewhere.

The more transmissible a pathogen, the more people must become immune in order to stop it.

Dr. Morens and Dr. Lipsitch agreed with Dr. Fauci that the level of herd immunity needed to stop Covid-19 could be 85 percent or higher. “But that’s a guesstimate,” Dr. Lipsitch emphasized.

“Tony’s reading the tea leaves,” Dr. Morens said.

The Centers for Disease Control and Prevention offers no herd immunity estimate, saying on its website that “experts do not know.”

Although W.H.O. scientists still sometimes cite the older 60 to 70 percent estimate, Dr. Katherine O’Brien, the agency’s director of immunization, said that she now thought that range was too low. She declined to estimate what the correct higher one might be.

“We’d be leaning against very thin reeds if we tried to say what level of vaccine coverage would be needed to achieve it,” she said. “We should say we just don’t know. And it won’t be a world or even national number. It will depend on what community you live in.”

Dr. Dean noted that to stop transmission in a crowded city like New York, more people would have to achieve immunity than would be necessary in a less crowded place like Montana.

Even if Dr. Fauci is right and it will take 85 or even 90 percent herd immunity to completely stop coronavirus transmission, Dr. Lipsitch said, “we can still defang the virus sooner than that.”

He added: “We don’t have to have zero transmission in order to have a decent society. We have lots of diseases, like flu, transmitting all the time, and we don’t shut down society for that. If we can vaccinate almost all the people who are most at risk of severe outcomes, then this would become a milder disease.” (C)

“Dr. Anthony Fauci, the nation’s senior official for infectious diseases, predicts the United States could begin to achieve early stages of herd immunity against the deadly coronavirus by late spring or summer. And if that happens, Fauci anticipates, “we could really turn this thing around” toward the end of 2021…

Fauci said if all goes according to plan, by the end of March or beginning of April more vaccines will be available to the general public.

“Once we get there, if in the subsequent months, April, May, June, July, we get as many people vaccinated as possible, we could really turn this thing around before we get towards the end of the year,” Fauci said…

“We still have a raging outbreak that we need to get under control, so at the same time as we’re administering the vaccine as quickly and as expeditiously as possible, we still have to implement the public health measures to prevent the surges we’re seeing throughout the country.” (D)

“The nation’s top infectious disease expert estimates that most Americans will have access to the new COVID-19 vaccines by mid-summer.

Dr. Anthony Fauci told Good Morning America on Tuesday that he expects to start vaccinating the general population “somewhere in the end of March, the beginning of April.”

He said the process could take up to four months to reach all Americans who want to receive the vaccine.” (E)

“As the nationwide vaccination effort ramps up, the federal government announced it has reached a deal to buy 100 million additional doses of Pfizer’s vaccine. Fauci expressed optimism in the availability of vaccines going into 2021. After the first round of doses goes to frontline health care workers, nursing home residents and others at highest risk, more and more of the American public will be able to get the shots in the months ahead.

“At the end of the summer, if we can get the overwhelming majority of the people in this country to accept vaccinations, I think, we will be in good shape towards approaching what all of us would want, a return to some form of normality,” Fauci said.

There have been more than 18 million confirmed COVID-19 cases in the U.S. since the start of the pandemic, and more than 322,000 Americans have died.

Asked about a mutated strain of the virus recently detected in the U.K. which may be more transmissible than before, Fauci explained that viral mutations are nothing new.

“These RNA viruses mutate all the time. The more infection and the more replication you have, the more likelihood is that you are going to get mutations,” he said, and noted that most viral mutations “have no relevant functional impact.”

He said there was no data thus far that indicated the new variant would withstand the vaccine.

“Having said that, we’ve got to take this seriously. We’ve got to follow it very carefully,” he cautioned.

Viruses like influenza that mutate more rapidly are usually combatted by a modified vaccine. Flu shots, for example, need modification “almost every year.”

However, he said the COVID-19 vaccines may not need such frequent updates. “This vaccine does not drift… it does not drift the way influenza does,” he said, and he expressed confidence that adjustments would be made if needed.” (F)

“On a recent Skype call with my grandmother, I broached the topic of the fast-arriving Covid-19 vaccines.

Advanced age brings wisdom, but it also brings an elevated risk of severe illness from infection with the coronavirus, so I wanted to prime her to get an FDA-approved vaccine as early as possible.

But as I was extolling the benefits of vaccination, I noticed a furrowed brow, a frown, and a look of uncertainty on her face. That took me by surprise. Surely someone who gets a flu shot every year and who raised two doctors shouldn’t feel anxious to get the Covid jab. But she clearly was.

That conversation left me worried not only about her safety but about the safety of our country. If my Grandma was feeling hesitant, millions of other Americans are probably feeling the same way. A nagging question popped into my mind: If vaccine distrust plagues our country, when will we be able to achieve herd immunity and transition to a new normal?

Herd immunity protects those with vulnerable immune systems. Here’s how.

Herd immunity occurs when a critical mass of people become immune to a pathogen like SARS-CoV-2, the virus that causes Covid-19. With enough people immune to the virus, the chain of transmission is halted, which provides indirect protection to individuals who aren’t immune.

Inspired by Dr. Jacob E. Jones, a family medicine physician at my hospital who made some predictions on the time required to achieve herd immunity based on vaccine adoption, I set out to answer my question with a model that uses the following variables and definitions:

The basic reproduction number R0 (pronounced R-naught). This number represents how infectious a pathogen is. An R0 of 2 means one individual infected with SARS-CoV-2 is likely to infect two other people. Currently, most estimates of R0 are between 2.5 and 4. For the sake of this thought experiment, I assumed an R0 of 4.

Base prevalence. This is the percentage of people immune to the virus at a given moment in time, either from acquired infection or vaccination.

Monthly infection rate. This is the percentage of people who become infected and acquire immunity to the virus every month.

Using just the basic reproduction number, it’s possible to calculate the percentage of people needed to achieve herd immunity:

If R0 is 4, then 75% of the population needs to acquire immunity to the virus in order to halt transmission.

In late September, a Stanford study estimated that 9.3% of Americans have antibodies against SARS-CoV-2. To be sure, antibody testing may suffer from low positive predictive value when the prevalence of infection is low, but this is the best estimate we have so far. I’ll use that as the base prevalence.

If the base prevalence at the end of September — eight months from the onset of the epidemic in the United States on January 21, 2020 — was 9.3%, the coronavirus has an infection rate of approximately 1.2% of the population per month. This back-of-the-envelope calculation is in line with estimates from the medical literature, with one study estimating 52.9 million infections in the U.S. from February 27 to September 30, or an infection rate of 1.3% per month.

Using the herd immunity threshold, the base prevalence, and the monthly infection rate, it’s possible to calculate the number of months (m) to achieve herd immunity:

If the virus is left to spread at its current rate with no vaccine, it would take 55 months from October 2020 to achieve herd immunity. That means May 2025. Even if I had assumed an R0 of 3, it would still take 48 months to reach herd immunity.” G)

“Vaccination offers two benefits, said Joshua Epstein, a professor of epidemiology at the NYU School of Global Public Health: direct protection of the person vaccinated, as well as the social benefit of vaccinated people not spreading the disease to others.

“If enough get vaccinated, the disease can die out on its own for lack of fuel,” Epstein said. “That’s the herd-immunity idea: Protect enough people that it has insufficient fuel to keep burning.” The goal of a vaccination strategy, he added, “is to tip the epidemic into that declining state.”

How many people need to get vaccinated

The vaccine candidate from Pfizer PFE, -0.45% and its German partner, BioNTech BNTX, -3.10%, showed 95% efficacy in protecting against COVID-19 in a late-stage clinical trial. Moderna’s MRNA, -5.33% vaccine showed about 94% efficacy.

It remains unclear whether the two vaccines, which received emergency-use authorization from the Food and Drug Administration this month, protect against symptomless COVID-19 infection or transmission. Preliminary data from Moderna’s trial suggested there may be a lower risk of asymptomatic infection after one dose, though further analysis is needed.

Estimates vary on what share of the population would need to get vaccinated against COVID-19 in order to achieve herd immunity, and experts warn that it’s hard to pin down a definitive figure just yet.

Both consist of two doses: Pfizer’s requires a second shot three weeks after the first, while the Moderna shots come four weeks apart.

At least 614,117 U.S. vaccine doses had been administered as of Monday morning, according to the Centers for Disease Control and Prevention; that tally only included Pfizer doses. Some 4.6 million doses of both vaccines had been distributed.

The U.S. has never reached herd immunity from natural infection with a novel virus; so far, vaccination has always been required. Estimates vary on what share of the population would need to get vaccinated against COVID-19 in order to achieve herd immunity, and experts warn that it’s hard to pin down a definitive figure just yet.

Moncef Slaoui, the Trump administration’s vaccine czar, told CNN in November that with the roughly 95% efficacy level demonstrated by Pfizer’s and Moderna’s vaccines, “70% or so of the population being immunized would allow for true herd immunity to take place.” “That is likely to happen somewhere in the month of May, or something like that, based on our plans,” he said.

Anthony Fauci, the nation’s top infectious-disease doctor, said during a Nov. 30 livestream with Facebook FB, -0.26% CEO Mark Zuckerberg that while he wasn’t yet sure what percentage of the population would need to get vaccinated against COVID-19 to achieve herd immunity, “I would imagine it’s somewhere between 75 and 85% at least.”

“If you have a highly efficacious vaccine and only 50% of the country gets vaccinated, you’re not going to have that umbrella of protection of herd immunity,” Fauci added. “What you really want is one, what we have, a highly efficacious vaccine — but you want 75, 85% of the people to get vaccinated.”

The percentage of people that will need to be vaccinated will depend on the actual vaccine efficacy in real life and any future vaccine efficacy, Landon added.

“If everyone got one of the mRNA vaccines and they worked about 90% of the time, we would need to vaccinate about 10% more than the ‘herd immunity’ target, whatever that may be,” she said. (mRNA technology, employed in both the Pfizer and Moderna vaccines, teach the body’s cells to create proteins that generate an immune response.) (H)

“County officials who have for years been planning for a mass vaccination said they are seeing that training and preparation — much of it funded by millions of dollars in federal grants — pushed aside as the administration of Gov. Andrew M. Cuomo has retained control of the state’s coronavirus vaccination program, including having hospitals rather than local health departments administer the doses.

Interviews with multiple county officials over the past week confirm that many are unclear why the governor’s administration has not activated the county-by-county system, a plan that included recent practice sessions in which members of the public received regular flu vaccines at drive-thru sites…

Gareth Rhodes, a member of Cuomo’s coronavirus task force, said the county health departments and their pre-designated “points of distribution” for vaccinations are still integral to the governor’s plan, which is being done on a regional rather than county-by-county basis. As part of that process, the state is gathering details from counties about their vaccination plans and capabilities.

“The state then refines and approves and we implement the regional plan, of which every single health department plays a large role,” Rhodes said. “It’s not like we’re sitting on 50 million vaccine doses. … We’re getting a very small number every week, and criteria for who is eligible is obviously very narrow at this point.”

Rhodes, who is helping lead the administration’s vaccination strategy, said the planning is complicated because every person needs to receive two doses of the same vaccine — roughly three weeks apart — and the vaccine being distributed by Pfizer must be kept in deep-freeze storage containers until it’s thawed for use.

Rhodes took issue with the idea that the county plans were being ignored. “We’ve been working very closely with them, have had a number of calls with them,” he said. “I think our goals are all the same; we want to get this thing done as quickly as possible and in the most efficient way as possible.” (I)


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