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https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31357-X/fulltext#coronavirus-linkback-header
Have deaths from COVID-19 in Europe plateaued due to herd immunity?
Have deaths from COVID-19 in Europe plateaued due to herd immunity?
There has been quite a bit of discussion regarding herd immunity. We wrote this commentary to summarise our thoughts. This commentary was peer reviewed. It does not ofcourse reflect the views of @TheLancet
It would be great if we had reached herd immunity. It would all be over and we could move on with our lives and go back to normal. But we just don't think there is evidence for this. i'll summarise our arguments. Look at the online supplement for figures and in the main tweet.
First, countries plateau at different levels of mortality per capita. As of 17 May 2020, Germany had 95 deaths per million population, the Netherlands had 332, and Italy had 525. If they have all achieved herd immunity, why are they all so different? These are countries that have
similar demographics, are neighbours, genetic similarities, good healthcare and probable similar prior exposure to other human coronaviruses. A simpler explanation is the levelling off of deaths at different plateaus is caused by differences between countries in the timing
with behavioural changes. Under this explanation these discrepancies can be explained by the timing and stringency of interventions. We don't know the best set of interventions yet, but these simple figures suggest they are a more likely explanation for controlling the virus.
Second, if you plot the deaths before lockdown, and the deaths in the 6 weeks after lockdown you get a pretty linear relationship (see figure). This means, the sooner you locked down, i.e. when there were fewer infections and thus fewer deaths, the less you had afterwards.
If herd immunity had already been reached, we would expect to see no correlation, or even a negative correlation. Instead, the observed positive correlation is consistent with the explanation that lockdowns are highly effectively curtailing transmission and deaths.
Third, serology. Serosurveys have been conducted in recent weeks and have shed important light on the progress of COVID-19 epidemics to date. None, save perhaps for the recently published Bergamo study suggest a prevalence of infection close to the herd immunity threshold.
Take 6 national serological studies and plot them we see a consistent pattern. Herd immunity would imply that the infection fatality rate is very low. There are too many deaths to be otherwise.
There has been substantial effort expended to prove COVID-19 is not a deadly disease, that the IFR is 0.01% or less, and that the stringent interventions employed have been an overreaction. We think little evidence to date supports this contention.
We see a strong linear relationship between seroprevalence (roughly the % that have been infected) and mortality. If we reached herd immunity then why is spain so heterogenous? Surely severity in spain does not differ by a factor of 10 between regions?
A more plausible explanation is these countries have been experiencing similar severity, but their seroprevalence differs because the epidemic did not progress so far (e.g Denmark). And yes, there are issues with serology, but remember when we all wanted them, now they are here?
They cannot just be disregarded. And yes, there is a lot of variation around the 1% infection fatality rate, its variable for a lot of factors we know and likely many more we are yet to discover. But the serology does suggest <0.1% is not likely at all.
In summary, these data strongly suggest we are not at herd immunity. Second waves are possible and indeed likely if we get too relaxed. So we need to find the economically, politically and socially sustainable way to ensure we do not need to take radical action again.
Is there a lot we dont know, ofcourse! I do not claim to know the truth or have some prescience, but just follow the data, write preprints, try to publish them, improve them via review, and then start again to better things. This tweets views are my own.
Thanks to @CommunityJameel @Imperial_JIDEA @lucy_okell @neil_ferguson @azraghani @SRileyIDD @ArisKatzourakis @flaxter @creswapi @axel_gandy @charliewhittak @MRC_Outbreak @d_spiegel and all the admin staff at the MRC center who make things possible but are thanked little
p.s (can you do p.s. on twitter?) - remember the figure from the Lancet Commentary is in the supplementary. And while I am at it thanks to @TheLancet for their speedy process and helpful editors and the reviewer who gave their time assessing our work.
