Publisher’s Note: As Vermont Independent readers know, we’ve advocated a BOTH/AND pubic policy approach to the “coronavirus pandemic” since March. Natural Herd Immunity is our species’ effective collective immunological response to any viral pandemic, and research is now revealing that the threshold for herd immunity is even lower than many have realized. Complete BMJ article here. Here are the highlights. We’re including the much-cited 70-90% threshold definition of herd immunity below, which scientists are now suggesting may be too high. Good news!

Calculating the herd immunity threshold

In theory, outbreaks of contagious disease follow a certain trajectory. In a population that lacks immunity new infections grow rapidly. At some point an inflection in this growth should occur, and the incidence will begin to fall.

The 1970s gave rise to a theory that defined this inflection point as the herd immunity threshold (HIT) and offered a straightforward formula for estimating its size: HIT=1−1/R₀ (where R₀ is the disease’s basic reproduction number, or the average number of secondary cases generated by an infectious individual among susceptible people). This simple calculation has guided—and continues to guide—many vaccination campaigns, often used to define target levels of vaccination.20

The formula rests on two assumptions: that, in a given population, immunity is distributed evenly and members mix at random. While vaccines may be deliverable in a near random fashion, from the earliest days questions were raised about the random mixing assumption. Apart from certain small closed populations such as “orphanages, boarding schools, or companies of military recruits,” Fox and colleagues wrote in 1971,21 truly random mixing is the exception, not the rule. “We could hardly assume even a small town to be a single homogeneously mixing unit. Each individual is normally in close contact with only a small number of individuals, perhaps of the order of 10-50.”

Nearly 50 years later, Gabriela Gomes, an infectious disease modeller at the University of Strathclyde, is reviving concerns that the theory’s basic assumptions do not hold. Not only do people not mix randomly, infections (and subsequent immunity) do not happen randomly either, her team says. “More susceptible and more connected individuals have a higher propensity to be infected and thus are likely to become immune earlier. Due to this selective immunization by natural infection, heterogeneous populations require less infections to cross their herd immunity threshold,” they wrote.22 While most experts have taken the R₀ for SARS-CoV-2 (generally estimated to be between 2 and 3) and concluded that at least 50% of people need to be immune before herd immunity is reached, Gomes and colleagues calculate the threshold at 10% to 20%.2223

Ulrich Keil, professor emeritus of epidemiology from the University of Münster in Germany, says the notion of randomly distributed immunity is a “very naive assumption” that ignores the large disparities in health in populations and “also ignores completely that social conditions might be more important than the virus itself.” He added, “Tuberculosis here is the best example. We all know that the immune system is very much dependent on the living conditions of a person, and this depends very much on education and social conditions.”

Another group led by Sunetra Gupta at the University of Oxford has arrived at similar conclusions of lower herd immunity thresholds by considering the issue of pre-existing immunity in the population. When a population has people with pre-existing immunity, as the T cell studies may be indicating is the case, the herd immunity threshold based on an R₀ of 2.5 can be reduced from 60% of a population getting infected right down to 10%, depending on the quantity and distribution of pre-existing immunity among people, Gupta’s group calculated.24

RESPONSE #1:

Feature Coronavirus

Covid-19: Do many people have pre-existing immunity?

BMJ 2020; 370 doi: https://doi.org/10.1136/bmj.m3563 (Published 17 September 2020)Cite this as: BMJ 2020;370:m3563 Read our latest coverage of the coronavirus outbreak

• Article
• Related content
• Metrics
• Responses

All rapid responses

Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles.Sort by Date PublishedOrder AscendingDescendingItems per page 510204060

Covid-19 immunity, covid vaccines, and influenza vaccines

The possibility that population immunity to Covid-19 is much higher than has been publicized and that the herd immunity threshold (HIT) could be as low as 10% comes as a revelation. (Doshi, BMJ 2020;370:m3563, Sept 17) I hope this information reaches public health authorities in the US where worst-case scenarios seem to be driving lockdowns, “warp speed” development of Covid-19 vaccines, and where fear of a “twindemic” is driving a stampede to influenza vaccine mandates—in California, Massachusetts, New Jersey, and Vermont, so far.

Influenza vaccine mandates are especially problematic. The most recent publication indicates that, when studied over several seasons, influenza vaccines are associated with increased mortality in the elderly. During six A/H3N2-predominant seasons vaccine effectiveness (VE) against all-cause mortality among elderly men was -16.6% (-32.2% to -1.1%). (Anderson et al, Ann Intern Med, 3 March 2020, Supplement Table 14) Over 14 seasons overall VE against all-cause mortality in elderly men was -8.9% (-19.6% to 1.8%). (Table 2 in Anderson et al) Furthermore, there is a strong geographic correlation between influenza vaccine uptake in the elderly and Covid-19 death rates. (www.bmj.com/content/369/bmj.m2184/rr-4) Although influenza vaccines provide modest, short term protection against circulating influenza viruses, the vaccines are consistently associated with increased risk of illness from non-influenza respiratory viruses (NIRVs). I am aware of eight studies published between 2011 and 2020 with odds ratios or hazard ratios between 1.06 and 4.91.

Six years ago Margaret McCartney asked “What use is mass flu vaccination?” and called for randomized trials. (BMJ 2014;349:g6182) A few infectious disease and public health experts have made the same demand. So far the authorities have not seen fit to comply….Recently Els Torreele warned that the rush to create a Covid-19 vaccine was likely to do more harm than good. (BMJ 2020;370:m3209, Aug 18. BMJ Opinion, Sept 16) His warning was reinforced by Fiona Godlee. (“Less haste, more Safety.” BMJ 2020;370:m3258, Aug 20) Their warnings could also apply to influenza vaccines, which I hope are heard by US authorities.

ALLAN S. CUNNINGHAM 18 September 2020

RESPONSE #2:

Nature to the Rescue?! Re: Covid-19: Do many people have pre-existing immunity?

Dear Editor,

I hope that there are sufficient people with natural Immunity to SARS-CoV-2. I also hope that the phenomenon of Herd Immunity comes in to play. The hope is that these two natural phenomena act like Moderator in a Nuclear Reactor.

These hopes come from the findings that people in certain localities show high percentage of people having Antibodies to SARS-CoV-2, ranging from 26 to 56 percent. 

Arvind Joshi, MBBS MD FCGP FAMS FICP