(Study) Herd immunity and the herd severity effect

Vaccination reduces morbidity and mortality by making infections and related diseases less common. A natural conclusion might be that breakthrough cases of vaccine-preventable disease would also become less severe. However, the opposite seems to be true for diseases that are more severe when acquired after childhood, according to the study by Nina Fefferman and Elena Naumova1 published in The Lancet Infectious Diseases. Their finding is somewhat counterintuitive: higher vaccination rates that approach herd immunity levels mean that fewer people overall get sick, but those who get sick might have much more severe illnesses than in previous generations.  The study is not open access

(Study) Dangers of vaccine refusal near the herd immunity threshold: a modelling study.


Our calculations show that negative outcomes are 4·5 times worse for measles, 2·2 times worse for chickenpox, and 5·8 times worse for rubella than would be expected in a pre-vaccine era in which the average age at infection would have been lower.


As vaccination makes preventable illness rarer, for some diseases, it also increases the expected severity of each case. Because estimates of case risks rely on data for severity generated during a pre-vaccine era they underestimate negative outcomes in the modern post-vaccine epidemiological landscape. Physicians and parents should understand when making decisions about their children’s health and safety that remaining unvaccinated in a predominantly vaccine-protected community exposes their children to the most severe possible outcomes for many preventable diseases.

VLA Comment:  Another study showing that it is the vaccinated that is putting the unvaccinated at risk. Added to these two studies, several new studies show that natural measles protect against cancer.  Go to link…

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