Historically, clinical trials have been conducted without adequately considering the inclusion of diverse population groups. This can reduce their validity and seriously compromise their results, as they fail to demonstrate the specific impact on each population group. As a result, social health inequities increase. In response to this situation, principal investigator Anna Ponjoan and Dr. Constanza Jacques-Aviñó, together with a team from IDIAP Jordi Gol, the Girona Vascular Health Group (ISV-Girona), the Dr. Josep Trueta Biomedical Research Institute of Girona, and the Canary Islands Health Service, carried out an exhaustive study to analyze whether the different clinical trials of COVID-19 vaccines reflected the various axes of social inequity among participants.

On the efficacy and safety of COVID-19 vaccines

Any clinical trial involving participants must demonstrate the efficacy and safety of the vaccines or medicines being evaluated. This essentially means that the tests carried out are effective in an initial phase and safe, that is, they do not cause significant adverse effects. However, the efficacy and safety of these studies may be reduced if they are not properly stratified according to population groups.

In this regard, clinical trials conducted during the COVID-19 pandemic should have addressed these axes of social inequity. However, according to the study, only sex or gender and age were considered, while other axes such as gender identity, sexual orientation, socioeconomic status, ethnicity, and obesity were overlooked. The researchers examined compliance with these axes, recognizing their significant impact on people’s health and the need for any trial to be evaluated while taking into account the specific axes affecting each individual.

Study methodology

Using the Rayyan platform, the researchers selected studies published on a wide range of clinical trials conducted to develop different coronavirus vaccines. From a sample of more than one thousand articles, Rayyan selected 63 articles evaluating 20 different vaccines, mainly in phase 2 or 3. The selected trials were conducted before February 2022, involved human participants, were published in English or Spanish, and included populations from Asia, Europe, and North America.

Lack of representativeness in clinical trials

The included articles were analyzed to determine whether they incorporated the proposed social inequity axes, focusing on the description of participant characteristics, losses during follow-up, and stratification of results according to efficacy and safety.

All studies reported participants’ sex or gender. However, other axes were less frequently represented: only 73.0% of studies reported ethnicity, 68.9% reported age groups, and 22.2% identified participants with obesity. Only one article described the age of participants lost to follow-up.

Thus, efficacy results were stratified by age in 61.9% of articles, by sex or gender in 26.9%, by race and/or ethnicity in 9.5%, and by obesity in 4.8%. Safety results were stratified by age in 41.0% and by sex or gender in 7.9% of analyses. Reports on participants’ gender identity, sexual orientation, or socioeconomic status were rare. Gender parity was achieved in 49.2% of studies, and sex-specific results were mentioned in 22.9% of analyses, most of which were related to women’s health.