Skip main navigation

Understanding Vaccine Efficacy and Effectiveness

TBD
An image of a vaccination with a
© BSAC

Many different endpoints are used in vaccine research to define efficacy depending on the pathogen, consequences of infection and transmission dynamics.

Commonly, outcome data from Phase III randomised controlled trials (RCTs) are presented as a proportional reduction in disease between vaccinated and control subjects to calculate a vaccine-attributable reduction. Outcomes may include:

Three different potential outcomes of RCTs; reduction in infection, reduction in severity of resultant clinical disease and reduction in infectivity.

If you need a text version of the image above, this is available as a PDF.

Such RCTs represent ‘best case scenarios’ of vaccine efficacy under ideal conditions in particular populations and provide key data necessary for vaccine licensure. However, vaccine efficacy does not always predict vaccine effectiveness – the protection attributable to vaccines administered in real-life conditions. For example, the effectiveness of rotavirus vaccines in children in low and middle-income settings was lower than the efficacy observed in children in high-income countries.

Equally, RCTs conducted in a particular age group or geographical setting may not predict effectiveness if more widely deployed. For example, alternative vaccine platforms or the addition of adjuvants are required for adequate immunogenicity of influenza vaccines in older age groups. For this reason, prospective studies of vaccine effectiveness in ‘real-world’ scenarios post-licensure are routinely needed.

In the current pandemic, it is crucial that we find out if a vaccine against COVID-19 is successful. We will discuss how this is done in the next few steps.  

© BSAC
This article is from the free online

Vaccine Development: Finding a Vaccine for COVID-19 and Future Pandemics

Created by
FutureLearn - Learning For Life

Our purpose is to transform access to education.

We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.

We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.

Learn more about how FutureLearn is transforming access to education