External validity of phase III trials on vaccines against SARS-CoV-2 to a middle-aged and elderly Western European population

Initial results from various phase-III trials on vaccines against SARS-CoV-2 are promising. For proper translation of these results to clinical guidelines, it is essential to determine how well the general population is reflected in the study populations of these trials. This study was conducted among 7162 participants (age-range: 51–106 years; 58% women) from the Rotterdam Study. We quantified the proportion of participants that would be eligible for the nine ongoing phase-III trials. We further quantified the eligibility among participants at high risk to develop severe COVID-19. Since many trials were not explicit in their exclusion criterion with respect to ‘acute’ or ‘unstable preexisting’ diseases, we performed two analyses. First, we included all participants irrespective of this criterion. Second, we excluded persons with acute or ‘unstable preexisting’ diseases. 97% of 7162 participants was eligible for any trial with eligibility for separate trials ranging between 11–97%. For high-risk individuals the corresponding numbers were 96% for any trial with separate trials ranging from 5–96%. Importantly, considering persons ineligible due to ‘acute’ or ‘unstable pre-existing’ disease drastically dropped the eligibilities for all trials below 43% for the total population and below 36% for high-risk individuals. The eligibility for ongoing vaccine trials against SARS-CoV-2 can reduce by half depending on interpretation and application of a single unspecified exclusion criterion. This exclusion criterion in our study would especially affect the elderly and those with pre-existing morbidities. These findings thus indicate the difficulty as well as importance of developing clinical recommendations for vaccination and applying these to the appropriate target populations. This becomes especially paramount considering the fact that many countries worldwide have initiated their vaccination programs by first targeting the elderly and most vulnerable persons.