COVID-19: Why herd immunity will likely occur much sooner than currently expected

In a paper sub­mit­ted April 1, 2020, a group of researchers from Italy and Switzerland had esti­mat­ed, via eval­u­a­tion of avail­able data from dif­fer­ent coun­tries and from sta­tis­ti­cal mod­el­ling, that by March 25, 2020, over 10 per­cent of the Italian pop­u­la­tion had already been infect­ed by the nov­el Coronavirus (i.e. more than 6 mil­lion peo­ple), and that the high­est prob­a­bil­i­ty was for the epi­dem­ic to end in Italy “with­in the first week of April or few days lat­er.”1

The authors based their mod­el­ling sce­nar­ios on the num­ber of deceased, as they right­ly assessed that this be the most reli­able num­ber regard­ing the spread of the epi­dem­ic avail­able at this time. Actual test­ing only cov­ers a small pro­por­tion of the pop­u­la­tion, and is high­ly unre­li­able, for rea­sons we have men­tioned in pass­ing in a pre­vi­ous arti­cle2 and which have been cor­rob­o­rat­ed by sig­nif­i­cant anec­do­tal evi­dence we col­lect­ed in our own per­son­al envi­ron­ment, includ­ing among friends and col­leagues in the med­ical com­mu­ni­ty. For their assump­tions regard­ing fur­ther devel­op­ment of the pan­dem­ic and its even­tu­al halt, the authors drew on offi­cial data from China and fit­ted their pro­jec­tion curve to the curve derived from this data.

Independently, a poll con­duct­ed by a lead­ing mar­ket research insti­tute, coor­di­nat­ed by a renowned epi­demi­ol­o­gist from the University of Milan, led to a very sim­i­lar esti­mate for the actu­al infec­tion lev­el. The poll had asked a rep­re­sen­ta­tive sam­ple of the pop­u­la­tion for symp­toms observed on them­selves (and had duly cor­rect­ed, as the authors assure, for the sub­jec­tive nature of the obtained data).3

As would be expect­ed giv­en lim­it­ed test­ing activ­i­ty and even capac­i­ty in most west­ern coun­tries, many oth­er indi­ca­tions have sur­faced for much high­er preva­lence of COVID-19 infec­tions than offi­cial data reveal.4

All this implies, of course, that the actu­al death rate from COVID-19 is far low­er than was ini­tial­ly feared, and will even­tu­al­ly set­tle at sig­nif­i­cant­ly less than half a per­cent of those infect­ed. The rea­son for the ini­tial fear of a much high­er lethal­i­ty, one can spec­u­late, is that the Chinese were con­front­ed with a sit­u­a­tion that in real­i­ty was, just as is now the case in Italy, much fur­ther devel­oped than ini­tial­ly esti­mat­ed, so that the Chinese like­ly thought they had a viral dis­ease as lethal as SARS 2003 on their hands, only that it appeared to spread sig­nif­i­cant­ly faster. This ini­tial assess­ment and the dras­tic actions tak­en based on it then shaped much of the pub­lic per­cep­tion of COVID-19 in the West, includ­ing ours.

In the lit­tle over a week since the pub­li­ca­tion of the two men­tioned esti­mates, it has become clear that the esti­mate made by the first-cit­ed group for a plateau­ing of the pan­dem­ic in Italy at around the time of this writ­ing does not con­form to real­i­ty. While the num­ber of dai­ly new deaths has shown signs of declin­ing, the num­ber of total deaths con­tin­ues to rise at a much high­er rate than fore­seen: Instead of an esti­mat­ed total of rough­ly 13,000 deaths by the time of this writ­ing and clear signs of plateau­ing, this num­ber has already sur­passed 18,000.5 The esti­mat­ed num­ber would have required the lock­down to yield sig­nif­i­cant results and to halt the pan­dem­ic in Italy before herd immu­ni­ty is achieved. The actu­al num­ber con­forms, in our view, much more close­ly to our own esti­mate, long held and men­tioned in a pre­vi­ous post,6 call­ing for effec­tive sat­u­ra­tion around the end of April. By “effec­tive sat­u­ra­tion” we mean herd immu­ni­ty and there­fore essen­tial­ly the end of the pan­dem­ic as regards Italy, not sim­ply a plateau­ing of active case num­bers that would drag out the pan­dem­ic for many more months, with even more dev­as­tat­ing eco­nom­ic con­se­quences, and with many more peo­ple dying “because of” instead of “of” COVID-19.7

The actu­al devel­op­ment of the num­bers indicates:

  1. Indiscriminate lock­down mea­sures do not work as expect­ed at least in a sig­nif­i­cant part of the west­ern world. Social inter­ac­tion can­not be total­ly pre­vent­ed (peo­ple have to go out to buy food), and where there is inter­ac­tion, there is the risk of infec­tion. For the South Korean solu­tion to rig­or­ous­ly test almost every­one and then iso­late only those test­ed pos­i­tive­ly it is obvi­ous­ly far too late.
  2. The phe­nom­e­non of sig­nif­i­cant pre- and pos­si­bly even com­plete­ly asymp­to­matic spread of the virus on the one hand and the unre­li­a­bil­i­ty of test­ing on the oth­er, both due to the observed typ­i­cal course of the infec­tion with ini­tial mas­sive viral repli­ca­tion in the throat that starts declin­ing around symp­tom onset (so that if peo­ple wait – or are put off – for too long to be test­ed, test­ing may yield a false neg­a­tive result), con­tribute to a much faster course of the pan­dem­ic than most have imagined.
  3. Therefore, over the com­ing weeks (Italy) to pos­si­bly two months that it should take to effec­tive­ly achieve herd immu­ni­ty in most of the west­ern world, the focus should be put on how best to pro­tect the espe­cial­ly vul­ner­a­ble and how best to man­age those infec­tions that either threat­en to or do indeed get out of hand, in order to max­i­mize those patients’ chances of recov­ery. Calls in recent days for an at least par­tial con­tin­u­a­tion of the lock­down for anoth­er 12 to 18 months, until a vac­cine may (or not) be avail­able, seem, viewed in light of the above, much misplaced.
  1. The COVID-19 infec­tion in Italy: a sta­tis­ti­cal study of an abnor­mal­ly severe dis­ease:[]
  3. Coronavirus, l’indagine: “Almeno 5 mil­ioni di ital­iani infet­tati”:[]
  4. E.g. from mea­sur­ing SARS-CoV-2 titers in waste­water, as has been done in a major urban treat­ment facil­i­ty in Massachusetts:[]
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What is the essence of someone pretending not to notice the essential aspect of the central allegation with respect to an essential matter to which he is an interested party, implicitly saying A while stating B? A refusal to engage in rational dialogue, which in turn is the only way to ultimately avert violence: an implicit declaration of (civil) war.

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What is the essence of someone pretending not to notice the essential aspect of the central allegation with respect to an essential matter to which he is an interested party, implicitly saying A while stating B? A refusal to engage in rational dialogue, which in turn is the only way to ultimately avert violence: an implicit declaration of (civil) war.