HIV Incidence in Prevention Trials and Observational Studies:
A Summary Table

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HIV vaccine clinical researchers depend on HIV incidence data to design, properly power, and conduct efficacy trials. Such data come from two main sources: Observational longitudinal cohorts in relevant populations and control arms of past HIV prevention efficacy trials. The Enterprise, in collaboration with the HVTN, IAVI, MHRP, and HPTN, created a quick-reference table to help researchers identify studies that may provide relevant incidence data.

How should this table be used?

The table contains two tabs, one listing efficacy trials and the other - observational studies. The table is intended to be used as a reference to identify studies that may have information useful for study design and statistical power calculations. The user is encouraged to refer to listed publications and other resources for a better understanding of the context in which the incidence was observed.

Critically, the user should consider the following limitations when interpreting incidence data derived from experimental trials and/or observational studies:

  • HIV incidence in the control group of a clinical trial may not reflect the background incidence in the community
    Efficacy trials provide an incidence estimate in a specific population in the context of a specific experimental intervention used as part of the trial. Incidence estimates reflect the effect of standard of care provided to the control group and may be lower than in the community from which the study population is drawn. The decrease may be large or small, depending on the offered prevention package in the trial and on the rate of uptake of the provided prevention package. Incidence observed in the trial may also be higher than background incidence in the community if high-risk individuals are recruited in the trial.
    With respect to HIV incidence data derived from observational studies, e.g. HIV tracking studies, it is important to keep in mind that prospective epidemiological studies are not always purely observational, but often provide study participants with regular HIV testing and risk reduction counselling, possibly leading to lower HIV incidence among study participants as compared to the actual incidence within their respective source communities.
  • The positive effect of clinical research in communities:
    Clinical research often not only affects HIV incidence within the study cohort itself, but can also have transforming effects on the community overall, leading to a decline in HIV incidence within the communities from which study cohorts are drawn.
    In addition, given the large number of past HIV prevention trials and the generally improving state of HIV prevention in communities around the world, incidence rates in many populations have been going down. Investigators assessing new HIV prevention strategies are trying to work with communities that have not yet been positively affected by past HIV prevention research. These communities cannot directly be identified by our summary table.
  • • The dynamics of available prevention packages over time:
    Available prevention packages are changing constantly due to the advancement in prevention technologies. Over the years, adequate prevention packages for study participants have evolved towards combination prevention packages, including not only the provision of free condoms but also STI testing and treatment, health education, risk reduction counselling, pre-exposure prophylaxis (PrEP), among others. Trial sponsors are striving to provide the most current, up-to-date prevention packages tailored to their specific study cohort. This leads to variations in trial protocols over time and across study cohorts. Hence, prevention packages are a very dynamic element of this table and need to be reviewed with caution.

Yearly updates:

This summary table was released on January 2017 and will be updated yearly. The next update is scheduled for the fall of 2017.

How to cite this table:

If you wish to acknowledge the use of this table or refer to the data contained in it, please cite as follows:

"HIV Incidence in Prevention Trials and Observational Studies: A Summary Table" by Global HIV Vaccine Enterprise, January 2017 version, accessed at

Tell us what you think:

This is the first version of a living document that will evolve through successive updates, changes, and adjustments. Because it may not be entirely comprehensive at this early stage, we encourage you to suggest additional studies to include. Also, if you used this tool for your own work, please give us feedback on the utility of this table and what kind of shortcomings you have encountered. We welcome any feedback that will help the improvement of this tool and will consider your suggestions for future updates. For any questions or feedback, please email

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