Optimal age targeting for pneumococcal vaccination in older adults; a modelling study

Abstract

Invasive pneumococcal disease (IPD) risk increases with age for older adults whereas the population size benefiting from pneumococcal vaccines and robustness of immunogenic response to vaccination decline. We estimate how demographics, vaccine efficacy/effectiveness (VE), and waning VE impact on optimal age for a single-dose pneumococcal vaccination. Age- and vaccine-serotype-specific IPD cases from routine surveillance of adults ≥ 55 years old (y), ≥ 4-years after infant-pneumococcal vaccine introduction and before 2020, and VE data from prior studies were used to estimate IPD incidence and waning VE which were then combined in a cohort model of vaccine impact. In Brazil, Malawi, South Africa and England 51, 51, 54 and 39% of adults older than 55 y were younger than 65 years old, with a smaller share of annual IPD cases reported among < 65 years old in England (4,657; 20%) than Brazil (186; 45%), Malawi (4; 63%), or South Africa (134, 48%). Vaccination at 55 years in Brazil, Malawi, and South Africa, and at 70 years in England had the greatest potential for IPD prevention. Here, we show that in low/middle-income countries, pneumococcal vaccines may prevent a substantial proportion of residual IPD burden if administered earlier in adulthood than is typical in high-income countries.

Fig. 1. Population demographics and invasive pneumococcal disease (IPD) burden.

a Among individuals who are aged ≥ 55 years, the proportion/share in annual age groups in Brazil, England, Malawi and South Africa as estimated from their national censuses, based on five years rolling average smoothed population counts to control for demographic stochasticity. b Number of IPD cases in five year age bands in older adults stratified by serotype in Brazil (2015–2017), England (2016–2019), Blantyre Malawi (2016–2019) and South Africa (2015–2018), reported from at least four years post-infant PCV introduction in each country, c Serotype-specific reported and predicted IPD incidence per 100,000 population between 55 years and 90 years in Brazil, England, Malawi and South Africa. The black circle represents estimated IPD cases per 100,000 population, the vertical line through the circle represents a 95% uncertainty interval in estimated IPD case number, the curve line is the exponential model fit and the ribbon represents a bootstrapped 95% confidence interval for the fitted line. The red and black points for England represent estimated IPD cases in the presence and absence of PPV23 vaccination, respectively.

Fig. 2. The impact of routine pneumococcal vaccination in older adults aged ≥ 55 years old (y).

The expected absolute number of total IPD cases averted for the rest of age cohort lifetime by vaccinating every older adult in the age cohort stratified by country and vaccine product, under the scenario of age-independent initial vaccine efficacy/effectiveness (VE) and waning VE in Brazil, England, Malawi and South Africa. The red lines represent cohort model mean estimates and the shaded red ribbon represents 95% bootstrap confidence intervals for the mean estimates. The X corresponds to the optimal age for pneumococcal vaccination. In Brazil, Malawi and South Africa, most cases are preventable at age 55 years whereas in England this is achieved at age 70 years.

Fig. 3. The efficiency of routine pneumococcal vaccination in older adults aged ≥ 55 years old (y).

The number of individuals needed to vaccinate to prevent a case in each age of vaccination, stratified by country and vaccine product, under assumptions of age-independent initial vaccine efficacy/effectiveness (VE) and waning VE in Brazil, England, Malawi and South Africa. The red lines represent cohort model mean estimates and the shaded red ribbon represents 95% bootstrap confidence intervals for the mean estimates. The X represents the optimal age for efficiency of pneumococcal vaccination. Efficiency of vaccination varies by waning VE assumption and country reflecting sensitivity in reported invasive pneumococcal disease cases.