Rating Evidence on the Effectiveness of Vaccines

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‘CO’ stands for corona, ‘VI’ for virus, and ‘D’ for disease.

There is a lot of data circulating about the effectiveness of vaccines against the coronavirus. Even experts can skid when they have to translate the numbers from scientific studies into concrete, understandable information. Explaining the effectiveness numbers and their meaning is not easy.

The vaccines are effective, but how effective exactly? Especially when it comes to vaccination to prevent diseases with COVID-19, it is important to be absolutely clear about its effectiveness and effectiveness in order to counter doubts and questions with clear information.

Say the effectiveness of the vaccine on the basis of messenger ribonucleic acid is given as 94%. This number shows how many cases of symptomatic COVID-19 illnesses are prevented by the vaccinations. This is calculated with 100 × (1 – disease rate with vaccine / disease rate with placebo). This becomes concrete if one looks at a population group that is similar to the group examined in the clinical study. A cumulative COVID-19 disease rate over a period of 3 months is considered, which is, for example, around 1% without vaccine, as was seen in the placebo arms of the vaccination studies.

With vaccine, 94% of these diseases that would otherwise occur would not occur. So actually only about 0.06% of people vaccinated would get COVID-19. On the other hand, it is commonly interpreted that 94% effectiveness means that 6% of all vaccinated people still get sick – versus 0.06% sick people with the correct meaning.

Then what does 94% mean? Misunderstood 6000 patients out of 100 000, actually only 60 patients. This precise description of the findings from the vaccination studies is also important for further predictions, for example when it comes to risk reduction in populations that are more exposed, exposed to higher numbers of infections or have an increased risk of disease.