Population-level herd immunity against Covid-19 will not be achieved in 2020

Herd Immunity would seem a dangerous strategy or objective bearing in mind the following:<p>- Immunity may only last a short time, in common with other Coronaviruses. Re-infection may be less severe, more severe, or not possible. We don&#x27;t know.<p>- Infection Fatality Rate is uncertain, but could be as high as 1%.<p>- Long term health effects are unknown, but for example some evidence suggests permanent lung damage is possible.<p>Significant areas of the globe have successfully suppressed the virus, and may even be looking towards eradication. Such countries are looking to establish &#x27;travel bubbles&#x27; or &#x27;green zones&#x27; between them and get back to normal (within their virus free spheres).<p>For other areas, it may be too late for suppression, or for societal reasons suppression may never have been practicable, in which case herd immunity as an idea could be considered a palliative.

We still don’t even know whether immunity to this lasts more than a few months (as is common with other coronaviruses). So it’s premature to talk about herd immunity regardless.

It&#x27;s interesting to compare how the world reacted to AIDS which is still a pandemic.<p>Before the hiv was understood in detail, policy responses were blunt or non-existent. Many kids including myself were taught to abstain from sex entirely, which of course is a policy which would work on paper but with which no one can comply in practice.<p>Here in Texas our lockdown has has little effect on the viruses rate of transmission. I believe that&#x27;s because like many southern states, we could never achieve good compliance.<p>More realistic policies which take into account the fact that young people are at far less risk for the virus will likely win the day. We can better support and sustain quarantine if it&#x27;s triaged for those at greatest risk.<p>Instead it Looks like policymakers will just let go of trying to control this in the US, and many older people will die unnecessarily.

Why would it? Everyone is trying to avoid getting infected (and dying). Isn&#x27;t that what we should do?<p>Herd immunity means &quot;it&#x27;s killed as many people as it could&quot;.

Anyone could have told you that. Or rather, anyone could have told you that <i>if we make some attempt at &#x27;slowing the curve&#x27; in order to try and keep the number of ICU-requiring cases below the number of available ICU beds</i> then it will take years if not decades to achieve herd immunity.<p>You could just go for broke, let everyone catch it at once, and RIP 5-10% of your population. Even then it&#x27;ll take most of a year to run its course and that year will be much, MUCH worse than just not being able to go to the pub or get a manicure.

The epidemiologists at JHU certainly understand this stuff better than I do, but a couple things about this article stood out to me. Is there an epidemiologist out there who could comment?<p>- The herd immunity threshold depends on the reproduction number of the disease (R0). There&#x27;s a basic reproduction number which is the rate they expect based on properties of the virus, and an effective reproduction number which is what ends up happening in reality. When effective R&lt;1 the virus starts to die out.<p>- The basic number can&#x27;t be changed but the effective number can be changed dramatically. Lockdowns and social distancing have already changed it, with varying levels of success in different locations.<p>- I have seen numbers thrown around that peg the herd immunity threshold for COVID-19 at 50-70%. This number is actually influenced by R, the lower R is, the lower your herd immunity threshold goes. JHU uses 70% here and that&#x27;s the most pessimistic estimate I have seen.<p>- Wouldn&#x27;t good, sustained social distancing lower effective R and thus produce a herd immunity threshold lower than 70%, perhaps much lower?<p>- New York is at 15-20% exposure already.<p>I read this article from the Oxford Centre for Evidence-Based Medicine a while back which observed that the early estimates for epidemics and pandemics are invariably worse than what ends up happening in reality, and it got me thinking. <a href="https:&#x2F;&#x2F;www.cebm.net&#x2F;covid-19&#x2F;global-covid-19-case-fatality-rates&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.cebm.net&#x2F;covid-19&#x2F;global-covid-19-case-fatality-...</a><p>My personal bias is that I don&#x27;t believe it is even possible, let alone wise, to keep people locked down on the time scales that are needed for controlling this virus, so they just kick the can down the road. But unprecedented levels of social distancing <i>might</i> be possible if we are smart enough. Every single person who works from home, wears a mask, or keeps their distance in public is helping.

With this mindset and approach the US will continue to have 20 million + unemployed all the way through Christmas.

&gt; Even in hotspots like New York City that have been hit hardest by the pandemic, initial studies suggest that perhaps 15-21%6,7 of people have been exposed so far.<p>That&#x27;s people with antibodies, not necessarily everyone who was exposed. There is zero information on seroconversion rates for mild and asymptomatic cases. We need to PCR-test a huge random sample, then follow up later with a serosurvey. Why are we not studying this? And why does nobody ever write a disclaimer listing their assumptions when making authoritative proclamations like this? It&#x27;s going to shred their credibility into dust by the time this is all over, even if half of their assumptions turn out to be correct.<p>Another study suggests that 20% infected could be enough for herd immunity, if individual variation in susceptibility is similar to the estimate for SARS-CoV-1: <a href="https:&#x2F;&#x2F;www.medrxiv.org&#x2F;content&#x2F;10.1101&#x2F;2020.04.27.20081893v1" rel="nofollow">https:&#x2F;&#x2F;www.medrxiv.org&#x2F;content&#x2F;10.1101&#x2F;2020.04.27.20081893v...</a>

I&#x27;m trying to figure out if this article is actually saying anything or saying effectively nothing.<p>&gt; Even in hotspots like New York City that have been hit hardest by the pandemic, initial studies suggest that perhaps 15-21%6,7 of people have been exposed so far.<p>(goes on to mention how many people are dying)<p>&gt; Some have entertained the idea of “controlled voluntary infection,”9 akin to the “chickenpox parties” of the 1980s. However, COVID-19 is 100 times more lethal than the chickenpox.<p>(goes on to completely dismiss whether that would actually lead to some level of herd immunity)<p>I get that the disease is more deadly. But is this one of those cases where it&#x27;s better to pull hard and rip the band-aid off in one go? Nobody seems to really want to broach this topic seriously.<p>&gt; To reach herd immunity for COVID-19, likely 70% or more of the population would need to be immune. Without a vaccine, over 200 million Americans would have to get infected before we reach this threshold. Put another way, even if the current pace of the COVID-19 pandemic continues in the United States – with over 25,000 confirmed cases a day – it will be well into 2021 before we reach herd immunity. If current daily death rates continue, over half a million Americans would be dead from COVID-19 by that time.<p>It&#x27;s unclear to me whether the author is stating that herd immunity would take too long under the condition that we completely opened up the global economy or if we all continued to stay isolated.<p>We&#x27;re definitely not going to reach 70% with the way things are.

I think herd immunity is an interesting point. Sweden is not there yet but its effective R value has already dropped below 1 a while back and it will continue to drop as the susceptible population continues to shrink.<p>Then there’s approaches like shielding that are interesting that are being discussed a lot. <a href="https:&#x2F;&#x2F;www.nature.com&#x2F;articles&#x2F;s41591-020-0895-3" rel="nofollow">https:&#x2F;&#x2F;www.nature.com&#x2F;articles&#x2F;s41591-020-0895-3</a><p>There’s something to note about this virus infection fatality rate: we don’t seem to have an agreed upon value for it and there is quite a window. It may depend on locale, population health, age, etc. But the 1% for the diamond princess is quite high and I think that number was cited for caution.

In the article that section about the cruise ship talked about voluntary self-infecting and how that would be risky (1-2% death rate).<p>What this completely ignores is that obviously only young and healthy people would attend those &quot;corona parties&quot; and thus the CFR of the voluntaries would rather be around 0%. And obviously those people wouldn&#x27;t immediately go see grandpa but instead self-isolate for three weeks.<p>I hate that so many are pretending that it&#x27;s like russian roulette when in reality the odds are so highly skewed.

I would liked to have read their opinions on Sweden.