Herd ImmunityFriday 21 June 2019
The term 'herd immunity' has been regularly appearing in the media as interested parties push for every greater uptake of vaccines. It is therefore important to know what herd immunity is and consider whether it can actually work.
The term 'herd immunity' heralds from an observation by A.W. Hedrich, in 1933 that measles outbreaks in Boston between 1900 and 1930 decreased when 68% of the children contracted the virus and became immune. There is no documented evidence that the theory was ever scientifically proven, however, it was adopted as scientific fact and applied as the basis for mass vaccination programs.
So how were the required vaccination rates to attain herd immunity calculated?
According to a 2015 article written by Marco Cáceres In the 1960s the US embarked on a mass vaccination program to eradicate measles. First of all a 55% vaccination rate was applied, but it failed to deliver the expected results. So the public health service changed the rate to 70-75%, but it failed to prevent measles. Each time the vaccination program failed to deliver eradication of measles, the percentage required for herd immunity was raised, until the 95% that is currently stated today. It is not clear how the required vaccination rate for herd immunity has been calculated or if there is any scientific basis to it.
Is Herd immunity working?
In the same article Marco Cáceres pointed out that despite 99% uptake of measles vaccination, China still documents measles outbreaks. A 2014 analysis of 60 years of compulsory vaccinations concluded that there has been a failure to attained herd immunity for any childhood diseases. In an article discussing MMR vaccine failure rates, Dr. Gregory Poland, Editor-in-Chief of the medical journal Vaccine, stated that we have this "paradoxical situation whereby measles in highly immunized societies occurs primarily among those previously immunized." Dr Poland cited an outbreak in Canada (October 2011) where "over 50% of the 98 infected individuals had received two doses of measles vaccine."