Why standard evidence may not fit high-risk children
Standard vaccine trials often aim for large, diverse populations to show clear statistical significance. But high-risk children—like those with underlying conditions or in remote communities—are often underrepresented, making it harder to detect benefits that are specific to them. In a randomized controlled trial (the PREVIX trials) involving Australian First Nations children, a high-risk group due to high rates of otitis media, PCV13 (13-valent pneumococcal conjugate vaccine) reduced moderate (disabling) hearing loss by 19 percentage points compared to PHiD-CV10 at 18 months (21% vs 41%, p=0.07) [1]. This difference was not statistically significant, likely because the sample size was small (only 42 and 49 children in each group), but the magnitude of benefit is clinically meaningful. This suggests that standard evidence standards, which rely on large trials, may miss important benefits in high-risk groups.
What evidence exists for high-risk benefits?
Despite the challenges, some studies show that PCVs can have substantial benefits in high-risk populations. In the same PREVIX trial, at 18 months, the prevalence of normal hearing was 36% in the PCV13 group versus 16% in the PHiD-CV10 group—a 19 percentage point difference (p=0.05) [1]. This suggests that PCV13 may help preserve hearing, which is critical for development and school performance in high-risk children. However, the effect was not consistent at later time points (differences of -3%, -12%, and -9% at 24, 30, and 36 months, respectively), and the authors noted the small sample size limited confidence [1]. This underscores the need for larger, dedicated studies in high-risk groups to confirm these potential benefits.
The gap between best-case and typical-case evidence
There's a clear gap between what we know from general population studies and what we need for high-risk children. For example, a 20-year surveillance study in Massachusetts showed that PCVs dramatically reduced invasive pneumococcal disease (IPD) by 72% in children overall, but in the PCV13 era, about one-third of IPD cases in children over 5 years had at least one underlying condition [3]. This indicates that high-risk children may still be vulnerable to serotypes not covered by current vaccines. Meanwhile, newer vaccines like PCV15 and PCV20 are being developed, but their evidence in high-risk populations is still emerging. For instance, PCV15 showed superior immunogenicity for serotype 3 compared to PCV13, but whether that translates to better protection in high-risk children is unknown [4]. Similarly, PCV20 is recommended for at-risk adults, but data in high-risk children are limited [5]. This gap means that for high-risk children, we may need to accept evidence from immunogenicity studies or smaller trials, rather than waiting for large efficacy trials that may never be feasible.
About These Sources
This answer is built on 5 peer-reviewed studies — published from 2023 to 2025, 3 from 2024 or later, 4 in Q1 journals, collectively cited 62 times — selected as the most relevant from 5 studies that passed quality screening, drawn from 48 papers retrieved from a database of over 500 million.
Sources used in this answer
Hearing loss in Australian First Nations children at 6-monthly assessments from age 12 to 36 months: Secondary outcomes from randomised controlled trials of novel pneumococcal conjugate vaccine schedules
In a randomized controlled trial (PREVIX) in Australian First Nations children, PCV13 reduced moderate hearing loss by 19 percentage points at 18 months compared to PHiD-CV10 (21% vs 41%, p=0.07), but the difference was not statistically significant due to small sample size.
Hearing loss at 6-monthly assessments from age 12 to 36 months: secondary outcomes from randomised controlled trials of novel pneumococcal conjugate vaccine schedules
This companion paper to the PREVIX trial reported similar findings: at 18 months, moderate hearing loss was 21% with PCV13 vs 41% with PHiD-CV10, and normal hearing was 36% vs 16%, but the effect was not consistent at later ages.
Invasive Pneumococcal Disease After 2 Decades of Pneumococcal Conjugate Vaccine Use
A 20-year surveillance study in Massachusetts found that PCVs reduced invasive pneumococcal disease by 72% in children, but in the PCV13 era, about one-third of cases in children over 5 years had at least one underlying condition, highlighting ongoing risk in high-risk groups.
PCV15, a pneumococcal conjugate vaccine, for the prevention of invasive pneumococcal disease in infants and children
A review of PCV15 (V114) in infants and children found comparable immunogenicity to PCV13 for shared serotypes, with superior immunogenicity for serotype 3, but whether this translates to better protection in high-risk children is unknown.
Recommendations on PCV20 vaccine in adults and at-risk populations
A narrative review on PCV20 recommends its use in adults and at-risk populations, but notes that data in high-risk children are limited, and ongoing studies will assess effectiveness.