Herd Immunity – what’s in a name?

“Herd immunity” recently made a controversial appearance in the context of the current COVID-19 pandemic. What does the phrase mean, where did it come from, and how helpful is it today?

As of March 2020, the OED defines it as, “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”.

The earliest use of the phrase can be traced to a 1917 report from the US Bureau of Animal Industry that dealt with a cattle infection causing death of unborn calves. A cow that had aborted was likely to become immune, and calves born and raised in such an affected herd were tolerant to the disease. The authors concluded that “a herd immunity seems to have developed as the result of both keeping the aborting cows and raising the calves”.

However, the senior author, Dr Adolph Eichhorn, Chief of the Pathological Division, made no reference to herd immunity in a monograph to which he contributed a major section on biological therapeutics just two years later. His biologically apt coinage does seem to have been picked up in US agricultural circles, but it was not universally adopted, with “immunity of the herd” being used instead.

The concept of herd immunity next appeared in British bacteriologist William Topley’s epidemiological studies of bacterial infection, which examined the resistance of a population of mice after immunising animals with suspensions of bacteria. He used “herd-resistance” to describe the natural resistance of individuals within a population. And he discussed the implications of his work with the “mouse herd” for the “human herd”.

The human herd entered this experimental realm at about the same time. In 1922, Surgeon-Commander Sheldon Dudley studied a diphtheria epidemic at Greenwich Hospital School. He found that the longer boys had been resident the greater the proportion who were immune, and that increases in immunity correlated with each outbreak. He extended such studies to other infectious diseases and used herd immunity to explain his findings.

In 1928, all boys in the school were actively immunised against diphtheria. The most senior became immune (Schick-test negative) twice as quickly as the most junior, suggesting prior exposure to the disease (see Figure). These results paralleled earlier work in animals, except for the fact that “a herd of human boys were used in lieu of the guinea-pigs”.

Dudley was unapologetic for using the prefix herd to denote the properties of a community, pointing out that psychologists had earlier popularized the phrase “herd instinct”. Besides, on evolutionary grounds, there was “little fundamental difference between a herd of deer, a herd of swine, and a herd of Homo sapiens”.

Notions of herd immunity have become more sophisticated in recent decades owing to the increased importance of vaccination. Today’s NHS website defines the benefits thus: “If enough people are vaccinated, it’s harder for the disease to spread to those people who cannot have vaccines. For example, people who are ill or have a weakened immune system”.

The reader is also directed to more information and an animation on the website of the Oxford Vaccine Group’s Vaccine Knowledge Project . This site suggests that a better name for herd immunity is “herd protection” because it helps to protect those especially vulnerable to infectious diseases. “Community immunity” appears as an alternative.

Conveying the value of herd protection or community immunity to the public will be critical in successful vaccination against COVID-19. One must worry that the lazy use of a century-old phraseology rooted in the farm, mouse lab and human guinea-pigs, as well as a contemporary profusion of alternative terms, may prove more of a hindrance than a help.

 

Words by Edward Wawrzynczak

 

Sources used:

  1. Horton, R. (2020) Offline: COVID-19 – a reckoning. Lancet, 395, 935.
  2. https://public.oed.com/updates/new-words-list-march-2020/.
  3. Eichhorn, A. & Potter, G.M. Contagious Abortion of Cattle. In: Farmer’s Bulletin 790, Washington DC: United States Department of Agriculture, 1917.
  4. Winslow, K. & Eichhorn, A. Veterinary Materia Medica and Therapeutics, Eighth Edition. Chicago: American Veterinary Publishing Co, 1919, pp.525-563.
  5. Beechy, L.P. (1920) Abortion disease in cattle. Bulletin of the Ohio State University Agricultural College Extension Service. Vol. XVI, No. 1.
  6. Smith, T., Little Further studies on the etiological role of Vibrio fetus. J Exp Med, 32, 683-689, R.B. &Taylor, M.S. (1920).
  7. Topley, W.W.C. & Wilson, G.S. (1923) The spread of bacterial infection. The problem of herd-immunity. J Hyg, 21, 243-9.
  8. Topley, W.W.C. Wilson, J. & Lewis, E.R. (1925) Immunisation and selection as factors in herd-resistance. J Hyg, 23, 421-436.
  9. Greenwood, M. & Topley, W.W.C. (1925) A further contribution to the experimental study of epidemiology. J Hyg, 24, 45-110.
  10. Dudley, S.F. (1922) The relation of natural diphtheria antitoxin in the blood of man to previous infection with diphtheria bacilli. Brit J Exp Pathol, 3, 204-209.
  11. Dudley, S.F. The Spread of Droplet Infection in Semi-isolated Communities. Medical Research Council, Special Report Series, No.111, London: HMSO, 1926.
  12. Anon. (1927) The spread of infection in schools and ships. BMJ, 1(3443), 34, 1 Jan.
  13. Dudley, S.F. (1928) Natural and artificial stimuli in the production of human diphtheria antitoxin. Brit J Exp Pathol, 9, 290-298.
  14. Dudley, S.F. (1929) Herds and individuals. J R Army Med Corps, 53, 9-25.
  15. Fine, P., Eames, K. & Heymann, D.L. (2011) “Herd immunity”: a rough guide. Clin Infect Dis, 52, 911-916.
  16. https://www.nhs.uk/conditions/vaccinations/why-vaccination-is-safe-and-important/.
  17. https://vk.ovg.ox.ac.uk/vk/herd-immunity.
  18. Betsch, C. et al. (2017) On the benefits of explaining herd immunity in vaccine advocacy. Nat Hum Behav, 1, 0056.
  19. Hakim, H. et al. (2019) Interventions to help people understand community immunity: a systematic review. Vaccine, 37, 235-247.

Can history help us in the COVID-19 epidemic?

1918 flu epidemic: the Oakland Municipal Auditorium in use as a temporary hospital. Photo by Edward A. “Doc” Rogers. From the Joseph R. Knowland collection at the Oakland History Room, Oakland Public Library. Digital copy via http://content.cdlib.org/ark:/13030/kt3q2nc9rt/?&query=

In this time of great uncertainty around the impact that Coronavirus disease 2019 (COVID-19) will have on populations and health systems globally, can we look to history to help us in its management?

Many have already drawn comparisons between COVID-19 and the 1918 influenza pandemic, also known as ‘Spanish Flu’. The 1918 influenza pandemic which spanned a couple of years from 1918-1920 infected 27 per cent of the world’s populations, and killed between 17 and 50 million, making it one of the deadliest pandemics in modern history.

While it may have occurred over a century ago, in many ways the situation with COVID-19 is similar to that facing nations in 1918. With no specific treatment or vaccination available except best supportive care, governments are turning to epidemiologists to help stop the spread and mitigate the damage caused by the disease.

A widely circulated graphic from the paper, ‘Public health interventions and epidemic intensity during the 1918 influenza pandemic’ by Hatchett et al. shows how differing public health responses resulted in different death rates between two American cities: Philadelphia and St Louis.

1918 excess mortality in philadelphia and St Louis

Excess P&I mortality over 1913–1917 baseline in Philadelphia and St. Louis, September 8–December 28, 1918. Source: Hatchett et al. https://doi.org/10.1073/pnas.0610941104

While authorities in Philadelphia became aware of the disease on 17 September 1918, they downplayed its significance and still allowed large social gatherings to take place including, a city-wide parade. They only implemented measures such as school closures and a ban on public gatherings on 3 October.

By contrast St Louis reported its first cases of the disease on 5 October and authorities mobilised containment measures rapidly on 7 October. The difference in the responses between both cities appear to have borne out in the excess pneumonia and influenza death rates seen in both cities.

Philadelphia experienced a peak weekly pneumonia and influenza excess death rate of 257 per 100,000 whereas St Louis experienced a rate of 31 per 100,000.

The above example appears to demonstrate the impact of early interventions such as social distancing to help contain the spread of the disease. If anything is to be learned from history a rapid implementation of such measures may be required to contain the spread of COVID-19.

For further reading on the impact of ‘Spanish Flu’, please refer to this post by Jane Orr.

 

Words by Flora Malein

 

Sources used:

Taubenberger JK, Morens DM (2006). “1918 Influenza: the mother of all pandemics”. Emerging Infectious Diseases. 12 (1): 15–22. doi:10.3201/eid1201.050979. PMC 3291398. PMID 16494711.

Spreeuwenberg; et al. (2018). “Reassessing the Global Mortality Burden of the 1918 Influenza Pandemic”. American Journal of Epidemiology. 187 (12): 2561–2567. doi:10.1093/aje/kwy191. PMID 30202996

Richard J. Hatchett et al. (2007) Public health interventions and epidemic intensity during the 1918 influenza pandemic. PNAS May 1, 2007 104 (18) 7582-7587; first published April 6, 2007 https://doi.org/10.1073/pnas.0610941104

Laughter is the best medicine

Anyone who has read doctor-turned-comedian Adam Kay’s best-selling ‘This Is Going to Hurt’ about his experiences on the obstetrics wards will be aware that medicine provides rich pickings for humour and satire.

But Kay is not the first person to draw on medical experiences to amuse his audiences. For as long as modern medicine has existed, medics and patients have been finding the humour in their experiences, helping to inform on attitudes and experiences from that time.

One such example is this excerpt from the October 1869 magazine, Punch. Written by Francis Cowley Burnand, a nineteenth century comic writer and playwright whose popular column ‘Happy Thoughts’ describes the difficulties and distractions of everyday life.

In this excerpt, Burnand turns his attentions to the doctor’s waiting room, in a scenario that will be very familiar to anyone who has ever made an appointment to see their General Practitioner. The narrator’s attempts to catch the doctor’s eye and jump to the front of the queue are ultimately dashed and he is forced to wait his turn like everyone else. The incident ends in embarrassment when he misplaces the doctor’s fee inside the lining of his coat.

The gentle observational humour illustrated in this column gives insight into the type of medical treatment available to the upper classes, while also demonstrating how little doctor’s waiting rooms have changed in the last 150 years.

The working relationship between doctors and nurses is also very neatly satirised in the following engraving from 1891. The Doctor asks the Nurse: “How is the patient this morning?” To which she replies, “Well – he has been wandering a good deal in his mind. Early this morning I heard him say ‘What an old woman that doctor is!’ – and I think that was about the last really rational remark he made.”‘

This comedic interchange about a delirious patient could just have easily occurred on one of today’s NHS medical wards.

As well as providing entertainment, humour and satire have also been used to highlight public health and social issues. In the following satirical cartoon from an 1893 issue off Punch, ‘Mr Punch’ remonstrates with a policeman about a quack doctor selling his ‘remedies’ on the streets of London. Saying, ‘And if Punch’s ready bâton lays its thwacks on any back with special zest, it is on charlatans and quacks.’

The cartoon highlights the movement against quackery towards the end of the nineteenth century, with a higher degree of ‘outcry’ against quacks that promoted false and unproven health claims for financial gain. While we are less likely to see ‘cure-alls’ pedalled on street corners, ‘quackery’ in the form of misinformation regarding vaccination and cancer treatments still exists as a scourge in modern medicine.

 

Flora Malein

The October 1869 Happy Thoughts article in full:

Image courtesy of Peter Burke

Sources used:

Chisholm, Hugh, ed. (1911). “Burnand, Sir Francis Cowley” . Encyclopædia Britannica. 4 (11th ed.). Cambridge University Press. p. 848.

The Wellcome Library

Tuberculosis, Philately and the history of the ‘Christmas seal’

Paris: Comité National de Défense contre la Tuberculose; Quimper: Comité d’Hygiène Sociale du Finistère, [between 1930 and 1939?]. Image Credit: Wellcome Collection, CC BY.

Christmas has long been recognised as a time of charity and fundraising. Perhaps familiar to some is the ‘Christmas seal’ – a label placed on post over the Christmas period – to raise awareness and funds for charitable organisations.

Christmas seals fall into a category known as ‘cinderella stamps’: items that resemble stamps but cannot be used in payment for postage

While the Christmas seal concept has been adopted to raise funds for many different types of charitable organisations, they have most closely been allied to raising awareness of tuberculosis. According to a New York Times article, the concept originated in Denmark in 1904, when a Danish postal worker called Einar Holbøll came up with the idea to sell the penny seals to raise money for children with tuberculosis.

Other countries quickly followed suit with fundraising seals being produced to support tuberculosis causes in Sweden, Iceland and Argentina.

At the time, tuberculosis was still one of the major causes of death globally. And despite the discovery of the M. tuberculosis bacillus by Robert Koch in 1882, no effective treatment had been found. Organised national efforts to combat the disease were looking for means to raise awareness and financial support for the disease. These campaigns can be seen as some of the very first public health initiatives, in which the financial contributions of ordinary people were used to fund treatment of a disease.

Picture credit: W. Dibb Private Collection.

The first American Christmas seals were produced in 1907 by a Red Cross volunteer called Emily Bissell, who adopted the idea to help raise money for a tuberculosis sanatorium in Delaware that was under the threat of closure if a sum of $300 was not raised.

Although she could not get permission to have the U.S. national postal service to print and distribute the seals, as they had in Denmark, she was allowed to privately sell the seals in the post office lobbies. The seals were such a success they raised over ten times the amount needed and became an annual tradition that raised major funds for The National Tuberculosis Association (now known as the ‘American Lung Association’). The American Lung Association continues to sell their Christmas Seals™. Selling tuberculosis Christmas seals has also funded major disease prevention programmes in countries, such as Canada, through chest X-ray screening or tuberculin tests.

The Cross of Lorraine

National Tuberculosis Association, 1940. Image Credit: Wellcome Collection, CC BY.

Many examples of the Christmas seals created to raise funds for tuberculosis charities contain the symbol of the double-barred cross. Symbolically known as the ‘Cross of Lorraine’, it was adopted as the symbol of the fight against tuberculosis at the International Conference on tuberculosis held in Berlin, 1902.

A French doctor – Gilbert Sersiron – proposed the emblem which had been the banner of Godfrey of Bouillon, one of the leaders of the first Crusades who successfully laid siege to Jerusalem and became it first ruler. In adopting this Crusader symbol, the cross became a symbol of the new, organised anti-tuberculosis ‘crusade’.

 

Flora Malein

 

 

 

 

 

You can read more about postal items and infectious disease in a previous post, here

Sources used:

The New York Times: https://www.nytimes.com/1989/12/24/style/pastimes-stamps.html

The American Lung Association: https://www.lung.org/get-involved/ways-to-give/christmas-seals/history.html

The Canadian Lung Association: https://web.archive.org/web/20111115234620/http://lung.ca/involved-impliquez/christmas-noel/history-histoire/index_e.php

TB Alert: https://web.archive.org/web/20090302074617/http://www.tbalert.org/about/cross.php

John, Simon (2017). Godfrey of Bouillon: Duke of Lower Lotharingia, Ruler of Latin Jerusalem, c.1060-1100. Taylor & Francis. ISBN 978-1-317-126300.

https://wellcomecollection.org/works/msbjucxs

https://wellcomecollection.org/works/hdh9a7xw