Not even “herd immunity” can fully protect us from …

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By Tyler Cowen

The issue of herd immunity – more specifically, whether certain cities or wider regions and regions acquire it earlier than expected and therefore have higher-than-expected protection against Covid-19 – has recently caught the attention of analysts.

Even if this hypothesis proves to be true, however, it still poses some really important challenges to the planet and imposes an ongoing and intense fight against the pandemic.

Evidence of herd immunity can be seen, for example, in Sweden, where the incidence and mortality rate has plummeted, although Swedes still do not wear masks or are meticulous in keeping their distance.

In London, bars, cinemas and many other places are now open, but the health situation seems stable, with low mortality rates.

Of course, both Sweden and the south-east of England were hit hard by the coronavirus early in the outbreak of the pandemic, so if they acquired herd immunity, it was probably because they saw a larger proportion of their population becoming infected with the coronavirus and developing thus some form of protection.

The “transmitters”

Some researchers claim that areas can acquire even partial immunity of the herd with exposure of at least 20% of the population, while in previous estimates there was talk of a necessary exposure of up to 70%. If this is indeed the case, this would be very good news for the areas most affected by the onset of the health crisis to date.

However, there are reservations. First, many hypotheses about herd immunity invoke the concept of “super-transmitters” – that is, a relatively small number of people representing a disproportionately large percentage of the virus transmission.

Maybe bartenders, church singers and bus drivers are the ones spreading the virus to so many others early in the pandemic. Now that these groups have been highly exposed and immune, according to this hypothesis, the virus is much more difficult to spread.

This logic makes some sense, except for one factor: that the identity of potential superconductors may change over time.

For example, chanters in the church choir may have been superconductors earlier in the winter, but with most church choirs shutting down in the midst of a pandemic, members of the U.S. Transportation Security Police (TSA) may be p. χ. the new superconductors in the country. Air travel, on the other hand, is growing steadily. The onset of winter and colder weather can, for example, turn waiters into a new set of superchargers, as more people will dine indoors.

In other words, herd immunity may be a temporary condition. Exactly the same economic and social shifts and changes brought about by the virus can cause people to switch to the role of potential “transmitters”, thus removing part of the acquired protection.

There is no guarantee of “permanence” of immunity

Related to this issue is the fact that areas with herd immunity are vulnerable to “invasion” by less protected areas of the same country.

The severely affected New York City may have acquired even partial herd immunity, but as the city begins to feel safe after a few months, residents of other areas and cities will begin to visit and live there, eliminating again part of the current level of protection.

New Yorkers themselves, meanwhile, will take more “risks” in their daily lives and be exposed to higher doses of the virus. Their current levels of immunity, while useful, will not make them invulnerable to all possible forms and degrees of exposure to the virus.

As it is worth saying once again, there is no guarantee of permanence in terms of herd immunity.

Another problem is global in nature and can prove to be really serious: one possible motivation for resorting to herd immunity is that a significant portion of the population was already exposed to similar coronaviruses, thus obtaining partial immunity to Covid-19. In essence, this “reservoir” of protected individuals has helped to slow down or even stop the spread of the virus earlier than one might expect.

There is, however, a pitfall. If this is the case, this case means that the virus is spreading much faster among groups with little or no immune protection. (If R = 2.5, but even 50% of the building population has protection, there is an R around 5 for the unprotected population, so that the total R is 2.5). Thus, if some parts of the world enjoy less protection from cross-immunity, Covid-19 is likely to “destroy” them even more healthily – and at lightning speed.

Of course, all this always moves in the realm of affairs. This scenario, however, may help explain the large number of Covid-19 cases and casualties in much of Latin America and possibly India and South Africa. Herd immunity, as a general concept, could mean a more dangerous virus for certain parts of the world and subgroups of the general population.

Continuous monitoring of the course of Sweden, the south-east of England and New York will probably reveal whether the herd’s immunity hypothesis is well-founded. But no matter what the evidence shows, this is not the time to be wary of the coronavirus threat.

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