Mea culpa - I've watched American presidential debate last night. Well, at least, the first part, but enough to chuckle when Mr. Trump made a joke, about receiving "therapeutic, not a cure" during his treatment for Covid-19. So, good, the man has learnt something. Yet seems, the media has not - as I will explain using another Nature News article, as below.

So, first things first, what is "herd immunity"? As Oxford English Dictionary defines it, it is a “resistance to the spread of a contagious disease within a population that results if a sufficiently high proportion of individuals are immune to the disease, typically as a result of having been vaccinated against it”.

Wait - typically as a result of being vaccinated?! But...but...Nature News says...Precisely - when the author writes "Many researchers say pursuing herd immunity is a bad idea" there is an awfully a lot of misleading going on, especially if a reader does not coming from biomedical sciences. So let us cut to the point.

"Herd immunity" is a resistance to the infection spread that occurs when sufficient number of individuals within the population is immune to the pathogen. How does it work? Well, let us use now-already famous Ro - basic reproduction number which gives researchers idea about the number of cases, on average, spawned by one infected individual in an otherwise fully susceptible, well-mixed population. Basically, Ro of 3 tells us that one infected individual infects three other individuals. In that context, herd immunity manifests when one infected individual comes in contact with three people with pre-existing immunity, so instead of 3 people, the same individual infects none and the further spread is prevented.

Still confused? Then imagine you are the infected individual. In the first scenario, you host a poker game for three of your friends and within the days a whole neighborhood is infected. In the second scenario, the infection never leaves your house. If we imagine a situation - which is a mix of first and second "poker game" - where two of your friends are immune and one is still susceptible, the neighborhood will still get infected, but at much slower rate. Ergo, herd immunity.

So why did I call this Nature News article misleading? For several reasons, as follows:

(1) Herd immunity has never been "a promise", "a proposal", or a "tool". Not even for Mr. Trump or, better said, scientists around him or even, Swedish scientists. This is why Lena Hallengren,, Swedish minister for health and social affairs, calls media reports "misunderstanding" - which is a mild way to put it. Herd immunity is a result - not a tool - a result that occurs when most of population comes in contact with infectious agent and develops immunity. It is also a result that occurs when we vaccinate sufficient number of people in the population. In other words, for decades, we have been pursuing herd immunity via vaccination and most of researchers would agree - it is a brilliant idea.

(2) Sure, herd immunity is typically discussed "as a desirable result of wide-scale vaccination programmes". However, typically, prior those discussions, we already have fully developed vaccine. So, "typically" may not be appropriate for "atypical" situation - such as Covid19 pandemic. Also "typically", throughout history ("Russian flu", "Spanish flu", "Hong Kong flu" ) - in the absence of vaccine - we also "typically" quarantined the ill not the healthy, "typically" applying so-called targeted infections strategy.

Which is not, once again, herd-immunity strategy (as such a strategy does not exist).

(3) Now, let's first observe what "ludicrous" Mr. Andersen said:

"“Attempting to reach herd immunity via targeted infections is simply ludicrous,” Andersen says. “In the US, probably one to two million people would die.”

First and foremost, this is speculation. Well, at best, we can call it an educated guess, but then again, most educated guesses (hypotheses) are worthless without evidence - and Mr. Andersen does not have any for several reasons:

a) Current data shows that lockdowns had no preventing impact on the number of deaths. Some countries with harshest lockdown, such as Peru, have the most deaths. And let's remind ourselves, the lockdown was never about preventing deaths, but preventing overload of health system. Moreover - to quote professor Ioannidis: "As of October 2020, there are >1 million documented deaths with COVID-19. Excess deaths can be caused by both COVID-19 and the measures taken." Hence, in absence of the vaccine, we tried lockdown or, as people came wrongly to believe - "to keep everybody safe". What are results of that strategy?

Here is my speculation - or my educated guess: in a near future, we are about to realise that the damage we caused to human health surpassed the damage done by the virus.

b) To paraphrase Swedish epidemiologist Tegnell, if some countries have lower mortality excess (number of deaths above expected yearly average) at start of pandemic, that does not necessary mean those same countries won't reach it within the year. The full lockdown strategy has only delayed inevitable, yet we are still far from both vaccine and any herd immunity. Also, we do not know what percentage of population in each country is "susceptible". However, what we do know is that data shows how early detection of cancer and early therapy save lives. So, I predict a drastic increase mortality caused by cancer. Or those people do not matter as much as Covid19 patients?!

c) I know the comparison of death rate between Scandinavian countries is very popular as a "proof," yet proves nothing. Here is why. As I probably mentioned, a person can be either immune or susceptible. To be able to compare Norway and Sweden, you need to be able to show their "susceptible" populations are similar. As explained by Ivor Cummins in one of my earlier posts, we actually have data that suggests that is not the case. There is a striking similarity between countries which experienced high mortality excess - most of them had mortality deficit during flu seasons of 2019 and 2018. Those countries include, for example, United Kingdom and Sweden. Yet, not Norway or Denmark. Additionally, there are other variables to consider, such as differences in eldery homes between Sweden and other Scandinavian countries, difference in levels of pre-existing immunity to other coronaviruses (currently unknown), prevalence of ACE receptor subtypes...

To conclude, the herd immunity is a not a strategy or a tool, but the end-result of pandemic whether you lockdown for several months, vaccinate or allow targeted infection. It is inevitable and lockdown only delays it. It is fantastic when vaccination is avaliable. Also, no data supports claims that targeted infection is ludicrous, especially now when we learned a lot about risk groups and infection fatality rate for different age groups.

If Mr. Trump could learn a difference between therapeutic and the cure, perhaps, it is time some scientists unlearn to misappropriate their training and positions for petty political points.

https://www.nature.com/articles/d41586-020-02948-4