Assessing the safety of vaccines is essential for maintaining public confidence and to identify true reactions which may affect the benefit-risk profile. For HPV vaccines safety has been particularly high profile in recent years with reports linking various adverse events to the vaccines. In this presentation I will cover methods for identifying safety concerns (signals), how they might be initially investigated and where necessary how/if robust epidemiological studies can be done to test hypotheses.
I will use a recent study done in England looking at HPV vaccines and Guillane Barré Syndrome as an example in which a signal was raised, data were rapidly examined and then a self-controlled case-series study done to assess the signal.
In this example the ecological study showed no evidence of an increased risk, but could also not exclude a risk of up to two fold. The epidemiological self-controlled case-series study confirmed no increased risk of Guillane Barré Syndrome following HPV vaccines (incidence rate ratio in the 3 months post a vaccine dose = 1.04 (95% CI: 0.47-2.28))
To enable robust and timely assessment of safety it is necessary to have a variety of systems in place to detect and investigate signals. Whilst for GBS this was possible with no risk seen, other events may be more difficult to assess if there are likely reporting biases and vague case definitions.
Andrews N, Stowe J, Miller E. No increased risk of Guillain-Barré syndrome after human papilloma virus vaccine: A self-controlled case-series study in England. Vaccine 2017;35(13):1729-1732. doi: 10.1016/j.vaccine.2017.01.076