Why is it that some people still get sick even though they have been vaccinated?

Last modified

December 20, 2016 @ 21:50 PM

No single vaccine confers 100% protection. However, immunisation is proven to significantly reduce the likelihood of an illness. Similarly, no medicine is 100% effective, but most of us use medicines prescribed by our doctors because there is a very strong chance that they will help make us better.

The Robert Koch Institute offers the following example to illustrate this point:
Imagine a measles epidemic occurs in a primary school. Half of the children are immunised, the other half not. Statistically, one can expect about 97 or 98 percent of the unprotected pupils to get sick – but only two to three percent of the vaccinated pupils.

However, the RKI notes that the influenza vaccination is less effective, protecting between 50% and 90% or people who are vaccinated, depending in their age and health status.

Some immunisations only prevent a particularly severe course of disease. A good example is the Bacille Calmette-Guérin (BCG) vaccination against tuberculosis. While the vaccine does not protect children from TB infection as such, it does reduce the risk of suffering the worst complications associated with TB.

Millions of people receive vaccines every year. Nothing in life is 100% safe nor 100% effective and vaccines are not completely free from side effects. The more common local reactions to an injected vaccine are redness and soreness at the vaccination site. There are only a few very rare serious side-effects among the millions of people vaccinated each year. It is the role of the public health decision makers in each country to ensure that the benefits that vaccination brings hugely outweigh any risks they may have.

For more information, see ‘Vaccination – 20 Objections & Responses’, produced by the Robert Koch Institute and Paul Ehrlich Institute