You might find Zach Mayer’s assessment at STAT of when we can expect enough people to be immune to SARS-CoV-2 tht the pandemic will be over interesting and informative:
For the sake of simplicity, I’ll ignore the phased rollout and imagine that all Americans have the choice to get vaccinated this April. Since both vaccine candidates are a two-shot series separated by three to four weeks, it may take at least an additional month to gain full immunity. At that point, in May 2021, the base prevalence of infection will be 17.7% (1.2% per month from October 2020, when the base prevalence was 9.3%).
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With just 39% of Americans getting a government-approved vaccine, the time to herd immunity is 19 months, meaning December 2022.
Nineteen months is no walk in the park. If 17.7% of Americans are already immune by May, and another 39% would readily get a Covid-19 vaccine, that leaves about 43% of the population who are vulnerable to infection but skeptical of vaccination.
Convincing roughly half of these skeptical Americans to take the shot, boosting Pv to 60.7%, shortens the time to herd immunity to two months, meaning July 2021.
I think the likelihood of having inoculated 39% of the population by April 2021 approaches zero. That would be 128 million people. You’d not just need to assume instantaneous simultaneous inoculations (as Mr. Mayer has), you need to assume
- Our borders remain closed
- Pfizer and Moderna are able to meet their own production estimates
- The supply of materials for the Pfizer and Moderna is sufficiently elastic to meet the demand within that timeframe
- Either the U. S. is the only country receiving the Pfizer and Moderna vaccines OR other vaccines complete their clinical trials and receive emergency use authorization by April 2021
- As many people as have said will actually get inoculated
- No unforeseen effects emerge now that we’re doing mass inoculations to discourage people from getting inoculated
just to hit the high spots. As Yogi Berra observed, in theory there’s no difference between theory and practice but in practice there is.
The estimate of when “herd immunity” will actually happen in the absence of inoculations is some time in 2025. In the presence inoculations, IMO a realistic estimate of when we can expect the pandemic to be over is some time between now and then and certainly no sooner than the 4th quarter of 2021.
Our first shipment arrived today so we begin vaccinations today. We are expecting it to take over a week to do 5000. I am finding that almost everyone who was on the fence now wants the vaccine. Seeing deaths and hospitalizations keep climbing influences people.
Testing. We are still short on testing supplies. I have 4 staff I would like to have tested but cant due to a shortage of reagents. In our area you cant get tested if you are asymptomatic.
On the creativity front we are trying out a new remote monitoring system. We have banks of computer screens being monitored buy college students overseen by medical people watching a nifty O2Sat monitor that people wear. This will let us admit people to surge beds without needing to have as much staffing and do so safely. I have been peripherally involved in this project for about 3 years now. We had worked with a company to help develop and spread this tech for another purpose initially but realized while back it could be modified for a situation like this. Nice to see it finally in action in working. (Ok, would have been better to never need it but since we did…)
Steve
Are you assuming children would be inoculated?
US population 18 and over is roughly 210 million, getting to 66% would take 280 million doses .
As far as getting back to normal,
normal is 8,000 deaths daily from all causes combined. So normal is a psychological perception of relative safety and lots of people are already there.
I’m not sure what he assumes. It looks as though he’s assuming that everybody would be inoculated regardless of age but it’s not stated in the article. Yes, that’s an issue.
First, he assumes R_0 is 4. That’s extremely high, most estimates are between 2.5 and 3.5. Starting listening to the This Week in Virology podcast this morning and I think they said most studies have shown 2.3 to 2.5. If its 2.3, then herd immunity is around 57% instead of his 75%. I’m no arguing for 57%, but I think he taking the extreme on the other end.
Also, he establishes prevalence of immunity already obtained by infection from a study that he acknowledges will under-report it. I think Youyang Gu’s approach was better, his model finds 19% of Americans have been infected, and he assumes that 99.9% of those have acquired natural immunity, but that this immunity declines over time.
Where I think the piece goes off the track is in another direction. Vaccines have not been shown to be 90% effective against transmission. Vaccines are primarily about disease prevention, transmission reduction is probable but secondary. I don’t know what number I would put in there, Youyang used 85%, maybe it should be the 67% suggested by Moderna, which was based only on one dose (though in turn this means more people acquire natural immunity while the vaccine is slowly rolling out).
@steve, my wife was told that she is engaged in ambulatory care and will get some sort of priority behind first responders. The hospital sent out an e-mail asking employees if they wanted the vaccine, and there were two responses available: Yes or Currently Undecided. I thought that was funny; seems to be a “nudge” move to encourage people not to reject the vaccine yet.
Governor only allocated 700 vaccines to our county, which is hovering just above 10% ICU capacity. Odd to direct regions to prioritize first responders and then have the State apportion vaccine distribution on the basis of per capita deaths (not necessarily where the first responders are).
@Grey, he is assuming that every person is the same in terms of their infectivity, they are all average, even though we know that some people (children, previously infected, socially removed) are not as likely to get infected as others (older, pre-existing conditions, residents of group homes).
If 20% of people are causing 80% of infections as has been suggested, then getting the right 20% of people is the most important thing. This type of heterogeneity is what leads to models of lower “effective” herd immunity levels, but that’s controversial.
I think he’s assuming average infectivity and susceptibility for everyone although we are pretty sure that neither is the case.
PD- Looking at our data, and that of a lot of others, primary care people are actually at pretty high risk. In our system many more primary care people, ambulatory if you will, got Covid from a pt than ICU staff who worked with Covid pts every day. Ambulatory people see patients when they come in coughing and not diagnosed yet. They generally are not as proficient at wearing PPE. I had a couple of former HAZMAT instructors among my people and I sort of count as one for that matter. Not many of those kind of folks in primary care. If I were in charge I would have primary care people in the first tier, which they are in our system. Not really sure how they decided to allocate within our state.
Steve
@steve, my wife doesn’t see any patients, she goes to the office and conducts therapy sessions over the phone or on zoom. A lot of her clients want in-person and remote initial assessments are crap.
My cynical view has been that sending the vaccines to regional hospitals allows them more opportunities to influence the process — they will be in constant communication with the various government actors. That may not be a bad thing.
My first relative tested positive this weekend, both my cousin and her husband, an ENT specialist. I have over thirty cousins, I would have thought others would be more likely to be first, but I do wonder a lot about the assumptions around testing a few days before a procedure. (Of course, it might not be the doctor, but I think she became a stay-at-home mom when they moved to Wisconsin)