ASTRAZENECA
1.3% ABSOLUTE RISK REDUCTION
PFIZER-BIOTECH
0.84% ABSOLUTE RISK REDUCTION
117 people would need to be vaccinated with the PFIZER jab to potentially prevent 1 case of symptomatic COVID
78 people would need to be vaccinated with the AZ jab to potentially prevent 1 case of symptomatic COVID
So, what is Risk?
In healthcare, risk refers to the probability of a bad outcome in people with the disease.
Different Risk Measurements
Absolute Risk (AR)
Absolute risk is the size of your own risk.
Absolute risk reduction is the number of percentage points your own risk goes down if you do something protective.
Absolute Risk Reduction (ARR)
Absolute risk reduction is the most useful way of presenting research results to help decision-making.
Relative Risk (RR)
If something you do triples your risk, then your relative risk increases 300%. Relative risk is often the same in people irrespective of their level of risk.
Relative Risk Reduction (RRR)
Relative risk reduction tells you by how much the treatment reduced the risk of bad outcomes relative to the control group who did not have the treatment.
Many reports in the media about the benefits of treatments present risk results as relative risk reductions rather than absolute risk reductions. This often makes the treatments seem better than they actually are.
For example, say a pharmaceutical company reported that medicine X reduced the relative risk of developing a certain disease by 25%. If the absolute risk of developing the disease was 4 in 100 then this 25% reduction in relative risk would reduce the absolute risk to 3 in 100.
What do vaccine manufacturers report?
Efficacy is reported in Related Risk Reduction
So, given Absolute Risk Reduction (ARR) is the best way to understand YOUR OWN RISK...
Absolute Risk Reduction (ARR) of COVID-19 Vaccines:
Number of people Needing to be Vaccinated (NNV)
The calculation highlights how many people need to receive treatment on order for 1 person to benefit from the treatment.
Sources:
Relative risk, relative and absolute risk reduction, number needed to treat and confidence intervals
Vaccine Relate Risk Explained (video):