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How we got herd immunity wrong

#1
C C Offline
https://www.statnews.com/2022/03/25/how-...ity-wrong/

INTRO (excerpts): In March 2020, not long after Covid-19 was declared a global public health emergency, prominent experts predicted that the pandemic would eventually end via herd immunity.

Infectious disease epidemiologist Michael Osterholm, who advised President Biden, opined in the Washington Post that even without a vaccine, SARS-CoV-2, the virus that causes Covid-19, would eventually “burn itself out as the spread of infection comes to confer a form of herd immunity.”...

[...]  Experts in the United Kingdom also spoke early on of herd immunity acquired through infection as a protective force that would ultimately end the epidemic. Planning on SARS-CoV-2 eventually becoming endemic, epidemiologist Graham Medley suggested that the U.K.’s initial strategy should be to “manage this acquisition of herd immunity and minimise the exposure of people who are vulnerable.”...

[...] Soon after this, some came to interpret the term as a do-nothing, “let it rip” strategy that would result in a huge number of avoidable deaths.

In response, policy quickly shifted to efforts to prevent all infections rather than targeting interventions at those at highest risk while accepting that a certain degree of viral transmission was unavoidable. Herd immunity in the absence of a vaccine soon became a dirty word. By May of 2020, a leading official in the World Health Organization announced that “humans are not herds” and that the term can lead to a “very brutal arithmetic.”

With the early arrival of vaccines in late 2020, prominent experts began promising that infection with SARS-CoV-2 was no longer inevitable. Herd immunity became defined as a percentage of immune individuals in a population that would stop transmission. Anthony Fauci captured this sentiment in May 2021 as a guest on “Face the Nation,” when he suggested that fully vaccinated individuals “become a dead end to the virus.” Once populations reached “the threshold of herd immunity,” he reiterated a month later, they would “see the infections almost disappear.”

Those mantras became the new plan: Get vaccinated to protect yourself, but also to protect those around you. Get to vaccine-induced herd immunity and the virus will virtually disappear from our communities.

As these failed to materialize, herd immunity has once again been dismissed as unachievable for Covid-19. As Fauci recently put it, SARS-CoV-2 will “find just about everybody.”

What went wrong?

The idea that vaccinating a certain percentage of the population would stop transmission of SARS-CoV-2 was a seductive but unhelpful description of herd immunity. This understanding comes from the so-called sterilizing immunity provided by infection or vaccination against diseases like measles. Sterilizing immunity means an individual can no longer be infected or infect others. Reach a certain percentage or “threshold” of this immunity in a population (around 95% for measles) and transmission comes to halt and the virus is eliminated.

This, however, is neither the exclusive nor even the most common understanding of herd immunity — and it is misleading for Covid-19. SARS-CoV-2 is not like the measles virus, but more like influenza, a virus that does not produce sterilizing immunity, returning every season like clockwork...

[...] Long before herd immunity came to be seen as an elimination threshold guiding mass vaccination campaigns, it explained why epidemics subside, reducing — but not eliminating — an individual’s risk of infection. Much like gravity pulls an object back to earth, herd immunity is the counterweight to sustained epidemic growth.

For SARS-CoV-2, herd immunity should not have been seen as an elimination threshold. Instead, it should have helped us understand that as immunity accumulated in the population, whether from infection or vaccination, the epidemic would recede before everyone was infected. Acknowledging that we couldn’t stop all infections, policy should have focused on minimizing the exposure of those already known to be at enormously increased risk of severe disease, while also limiting the harms caused by prolonged restrictions... (MORE - missing details)
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#2
Leigha Offline
Is ''we'' code for Dr. Fauci? Wink
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