“Herd Immunity” Debunked

Herd immunity. The indirect protection for individuals who are not immunized that occurs when a large percentage of their surrounding population has become immune through vaccination such that the likelihood of exposure of a vaccine-naive member of the general population to the infectious disease is substantially reduced.

Herd immunity (also called herd effect, community immunity, population immunity, or social immunity) is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, whether through previous infections or vaccination, thereby providing a measure of protection for individuals who are not immune. In a population in which a large proportion of individuals possess immunity, such people being unlikely to contribute to disease transmission, chains of infection are more likely to be disrupted, which either stops or slows the spread of disease. The greater the proportion of immune individuals in a community, the smaller the probability that non-immune individuals will come into contact with an infectious individual, helping to shield non-immune individuals from infection.

Individuals can become immune by recovering from an earlier infection or through vaccination. Some individuals cannot become immune due to medical reasons, such as an immunodeficiency or immunosuppression, and in this group herd immunity is a crucial method of protection.

“Herd Immunity” Debunked

The term “herd immunity” was first used in 1923. The term, ‘herd immunity’, was coined by researcher, A W Hedrich, after he’d studied the epidemiology of measles in USA between 1900-1931. It theoreticaly should be a form of protection from infectious disease that occurs when a large percentage of a population has become immune to an infection. It was recognized as a naturally occurring phenomenon in the 1930s when it was observed that after a significant number of children had become immune to measles, the number of new infections temporarily decreased, including among susceptible children. Mass vaccination to induce herd immunity has since become common and proved successful in preventing the spread of many infectious diseases. Opposition to vaccination has posed a challenge to herd immunity, allowing preventable diseases to persist in or return to communities that have inadequate vaccination rates.

Herd Immunity Calculator

Disease-conferred immunity usually lasted a lifetime. As each new generation of children contracted the infection, the immunity of those previously infected was renewed due to their continual cyclical re-exposure to the disease; except for newly-infected children and the few individuals who’d never had the disease or been exposed to it, the ‘herd immunity’ of the entire population was maintained at all times.

Vaccine induced immunity is depends on several variables such as vaccination coverage, efficacy of the vaccination, it’s duration and the treshold of the immune population needed for existence of the herd immunity.

With this calculator you can calculate whethet there was or not, a herd immunity present in allmost every part of the world in given year in the past.

The variables are as follows:

• Type of the vaccine
• vaccination coverage for a given vaccine in a chosen year (data taken from WHO) from as late as 1980
• efficacy of the given vaccine (data taken from the producers declarations).
  • Please note that the efficacy of the vaccination is taken as of the antibody developed (not by its efficacy,) since the presence of the antibodies do not automaticali mean immunity from a given desease, however, the presence of antibodies derived from vaccination is TAKEN as vaccine eficacy in this calculation, while in reality it is lower.
  • Furthermore, there are court cases regarding the producer’s misleading for the efficacy of the vaccines.
  • You can change it manually (if you know that it is different)
• Duration (i.e. presence of the antibodies) of the immunisation from the vaccine. Various scientific studies have different results. The highest numbers have taken as a calculation base.
  

  Vaccine	Duration	Study
  Measles	27y	(Ramsay ME, 1994)
  Mumps	15y	(JID, 2008)
  Pertusis	5y	(Al Dajani, Scheifele, PCH 2007)
  Diphteria	7y	(Girr, Fisman, Padiatrics 2015)
  HiB	10y	(Vaccine, 2015)
  Hepatitis B	6y	(EJE, 1995)
  OPV	15y	(WHO)
  IPV	6y	(WHO)
  Yellow fever	10y	(Ammana, Slifka ERV, 2016)
  Rotavirus	1y	(Pediatrics, 2012)
  BCG	20y	(Lancet, 2016)

  • You can change it manually (if you know that it is different)
• Age of the Last vaccination for the chosen vaccine. Allthouh the schedule slightly differs from country to country, US CDC schedule was used in the calculation as it wit the most late age recomended)
• Population pyramid correction.

• • As it is clear that not allways equal aged people live in each country, a correction is needed , especially in the cases of countries with young population. The numbers are aproximately taken by the region.
  • You can change the correction value to mach the country more precisely.
• Herd immunity threshold – Minimum of the immune population (HIT – Herd immunity Threshold) in order a herd immunity to be present. The World Health Organisation recommends a threshold of 95 per cent immunization coverage to achieve so-called ‘herd immunity’.

The result shows if there was a herd immunity in the chosen country/region in the chosen year for the chosen disease.

References:

• How herd immunity works. http://rocs.hu-berlin.de/D3/herd/
• C. Betsch, R. Böhm, L. Korn, C. Holtmann, On the benefits of explaining herd immunity in vaccine advocacy, Nature Human Behavior, 1, 56 (2017)
• D. Brockmann, Public Health: This mesage must be herd, Nature Human Behavior (News & Views), 1,65 (2017)
• Herd Immunity Calculator. http://www.herdimmunitycalculator.com/web/site/about
• Package Inserts and Manufacturers for some US Licensed Vaccines and Immunoglobulins. http://www.vaccinesafety.edu/package_inserts.htm