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,

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.
  • 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 treshold - Minimum of the immune population (HIT – Herd immunity Threshold) in order a herd immunity to be present.

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