Assessment of Length and Readability of Informed Consent Documents for COVID-19 Vaccine Trials

Informed consent is a fundamental element of research ethics. The COVID-19 vaccine trials are high profile trials that have enrolled more than 100 000 participants. Consent documents must be succinct and understandable to ensure informed voluntary participation.

To assess how well informed consent documents of the COVID-19 vaccine trials achieve the ideal of being succinct and understandable, and to create a shorter, more readable document.

This quality improvement study collected and analyzed the informed consent documents used in 4 COVID-19 vaccine phase III randomized clinical trials to quantitatively assess readability and length and, based on this analysis, created a measurably more accessible informed consent document. Analysis was conducted from October 2020 to January 2021.

The main outcomes were number of words (measured as word count), time-to-read (measured at reading speeds of 175-300 words per minute), language complexity (measured using Flesch-Kincaid Grade Level assessment), and readability (measured using Flesch Reading Ease Score). Secondary outcomes included clarity of how the placebo group could access the vaccine if it is proven safe and effective. The study also examined the length and readability of an improved consent document.

The 4 informed consent documents were a mean (range) of 8333 (7821 to 9340) words long, with a mean (range) 35 (32.6 to 38.9) minutes to read at 240 words per minute. All documents exceeded grade 9 language complexity and scored lower than 60 in the formal reading ease metric, which constitutes difficult. Only 1 document specified that participants in the placebo group might receive vaccine. It was possible to write a document in fewer than 3000 words with a grade 7 to 8 reading level and a formal readability score that was not difficult.

These findings suggest that existing COVID-19 vaccine informed consent documents were too long, difficult to read, and exceeded grade 9 in language complexity. It was possible to create a shorter, more readable informed consent document for these trials.