Fact check: How many senior women were included in the COVID vaccine clinical trials?

1. Why the question matters: senior women at higher risk but poorly counted

Seniors, and particularly older women, faced disproportionate morbidity and mortality from COVID-19 during the pandemic, making their representation in vaccine trials a public-health priority. The systematic review concluded that older adults were markedly underrepresented in phase II–III randomized vaccine trials, with fewer than 10% aged over 65 and less than 1% over 85, implying trial populations did not reflect those most at risk ^[1]. This lack of representation limits the evidence base for safety and efficacy specifically in senior women, constraining clinicians’ ability to make fully informed recommendations for this demographic ^[1].

2. What the published evidence actually reports about numbers

Peer-reviewed synthesis found clear numeric shortfalls: <10% of participants were older than 65 and <1% were older than 85 in the evaluated phase II–III COVID-19 vaccine trials, which necessarily includes senior women as a subgroup ^[1]. Separate work on trial design and enrollment documented exclusion of pregnant and lactating participants in the vast majority of vaccine trials — 97.8% excluded pregnant people and 81.1% excluded lactating people — underscoring an institutional pattern of narrow eligibility ^[2]. These figures illustrate both age and reproductive-status gaps in inclusion criteria ^{[2] [1]}.

3. Where the evidence is silent: trials in long-term care settings

Studies that focused on residents of long-term care facilities shed light on outcomes in an older population but did not directly answer how many senior women were included in the primary phase II–III vaccine trials. The GeroCovid Vax study examined sex differences in efficacy and safety among long-term care residents, offering insights into real-world responses in older adults but not trial enrollment proportions ^[3]. Consequently, evidence from care settings complements but does not replace the enrollment data reported in systematic reviews that evaluated randomized clinical trials ^{[3] [1]}.

4. How exclusion criteria shaped trial demographics

A dominant factor was explicit exclusion: the vast majority of vaccine trials excluded pregnant and many excluded lactating individuals, reflecting institutional caution and regulatory conservatism during the pandemic ^[2]. Although this exclusion targets reproductive status rather than age, it signals a broader pattern of restrictive eligibility that can indirectly affect representation among older women, particularly those with caregiving roles or health complexities. The combination of explicit exclusions and passive recruitment barriers produced trial cohorts that were younger and less diverse than the populations at highest risk ^{[2] [1]}.

5. Conflicting signals between randomized trials and observational studies

Randomized phase II–III trials show marked underrepresentation of older adults, while observational studies in long-term care settings report on vaccine performance among seniors after authorization, filling some evidence gaps ^{[1] [3]}. This produces a two-tiered evidence landscape: limited randomized-trial data for regulatory evaluation and richer post-authorization observational data for real-world effectiveness in seniors. Policymakers and clinicians thus had to rely on observational analyses to understand vaccine effects in senior women, because trial enrollment numbers were insufficient to yield precise subgroup estimates ^{[3] [1]}.

6. Implications for safety and efficacy conclusions in senior women

Because fewer than 10% of trial participants were over 65 and under 1% over 85, subgroup analyses for senior women lacked statistical power to detect differences in efficacy or rare adverse events. The resulting uncertainty meant that regulators and clinicians had limited randomized-trial evidence specific to senior women at the time of emergency use authorizations. Observational data from long-term care populations provided supportive safety and efficacy signals, but these cannot fully substitute for well-powered randomized-subgroup estimates ^{[1] [3]}.

7. What was omitted and why that matters for interpretation

The reviewed studies document enrollment shortfalls and exclusion patterns but do not provide a detailed breakdown of senior women by age strata, comorbidities, or race/ethnicity within trial cohorts, leaving crucial intersectional questions unanswered. The systematic review reports overall percentages for older adults but stops short of granular counts for senior women specifically. This omission constrains definitive statements about how many senior women were enrolled and whether those enrolled reflected the diversity of the at-risk population ^{[1] [2]}.

8. Bottom line for policymakers, clinicians, and the public

The aggregate evidence shows clear underrepresentation: phase II–III vaccine trials included very few participants over 65 (under 10%) and almost no participants over 85 (under 1%), while many trials excluded pregnant and lactating people, indicating systematic eligibility restrictions that affected representation overall. Observational studies in long-term care settings supplied post-authorization evidence on outcomes for older adults, but the randomized-trial record leaves unanswered questions about precise counts and subgroup-specific risks for senior women, highlighting the need for better trial inclusion practices in future vaccine development ^{[1] [3] [2]}.