Got to say I am trying to understand the herd immunity concept as well and falling short with COVID-19.
With a basic reproductive rate of around 3, it has been calculated that about 70% of population need to be infected. With a fatality rate of 0.5-1%, about 0.35-0.7 percent of a country's population will die! That seems a bit...hmm..bad! The biggest assumption we seem to make with the herd immunity approach is that surviving infection once creates immunity in the host. With COVID-19 that seems to be still a rather big unknown and seems to completely undermine the approach towards herd immunity. The way I see it, herd immunity would work well only when we have a vaccine (and second best when we have clear proof of immunity after infection, but at the cost of rather high number of fatality) and not as a preventive measure. Talking of the Dutch approach, I find it rather astounding that the PM says two things in the same breath - we don't seem to know what kind of contribution children have made to spread of the virus, the study results will come out in June but hey, let us start the primary school (which is the least affected by a month or two of missed or virtual schooling) in May, because.... (I live in Amsterdam, have primary school going kids so I find this whole approach very weird, especially given that before the school closed there were 3 confirmed cases of kids/parents who kept coming to school with early symptoms!) Regards, Srijith On Wed, Apr 22, 2020, at 2:42 PM, Alaric Snell-Pym wrote: > On 22/04/2020 12:11, Amit Varma wrote: > > On Wed, Apr 22, 2020 at 4:28 PM Udhay Shankar N <[email protected]> wrote: > > > >> > >> I assume you mean that it is not a good thing to actively work towards. > >> This also presumes that teh authorities can affect this outcome one way or > >> another. > >> > > > > Well, the idea is to delay and mitigate till a vaccine is ready, while > > treatment protocols that will lower mortality also evolve at the same time. > > Also, controlling the spread means that the number of people seriously > ill at any one time isn't greater than the local health service capacity > to give them quality care. > > One big unknown that's making it hard to say what's right to do - and > therefore giving licence to various nutjobs to claim that any given > strategy is wrong with great certainty - is that we don't really know > how many people are infected. > > *MAYBE* COVID is highly contagious but not very serious, with only a > fraction of people showing anything more than a mild cough, and a tiny > fraction getting seriously ill. It's already been spreading for months, > and we only noticed it when enough people had it to make a notable > number of people properly sick. We've all mainly had it already and > we're nearly at herd immunity and all this lockdown stuff is barely > necessary as we're unlikely to overrun health services unless we let it > get REALLY out of hand; the worldwide confirmed-infected and > confirmed-dead-of-covid rate is mainly just rising as more testing rolls > out and we've already plateaued, with the lockdowns just flattening out > the tail end of the rise to the plateau a bit. > > *MAYBE* it's actually pretty rare, and the published infection figures > from various nations are nearly all the people who have it, because > almost all people who have it show enough symptoms to get noticed and > tested, and quite a high fraction of them get seriously ill. In which > case, we're sitting on a ticking time bomb of it getting out of hand in > the population. > > There's some evidence for the former due to a few random population > sampling exercises, but the only way to really know either way is to > test as many people as possible. And to avoid bias in the testing, test > the population at random, rather than just people who start coughing, as > otherwise we won't know how many people are asymptomatic carriers. Test > people who died of lung failure, so we know whether to count them or not. > > > Also, it is impossible in India, except for privileged elites like us, to > > separate the vulnerable from the non-vulnerable. So many poor in congested > > cities, more co-morbidities than other nations, and a horrendous healthcare > > system -- there would have been carnage. (There still might be carnage down > > the road.) > > :-( > > > -- > Alaric Snell-Pym (M7KIT) > http://www.snell-pym.org.uk/alaric/ > > > Attachments: > * signature.asc
