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In the U.S., the Centers for Disease Control and Prevention (CDC) recommends routine pneumococcal vaccination for all adults 鈮�65 years old. Vaccination is also recommended for adults ages 19 through 64 years if they have specific chronic conditions or other risk factors. For both age groups, the CDC suggests regimens based on previous pneumococcal vaccines received, including cases in which the person鈥檚 vaccination status is unknown.¹ 

Those are the recommendations for patients in the U.S. However, the optimal age at which a single dose of pneumococcal vaccination may prevent most cases of invasive pneumococcal disease (IPD) in older adults may vary from country to country, according to a modeling study recently reported in Nature Communications.²

Lessening the burden of IPD

A multinational team of investigators found that vaccination at 鈮�55 years of age was the 鈥渕ost effective strategy鈥� to reduce the burden of IPD in the low- and middle-income countries they studied, whereas vaccination at age 70 was a preferable strategy in their high-income model.²

The group鈥檚 analysis revealed that a country鈥檚 overall age demographic, age-related incidence of IPD, and efficacy of the vaccine used impacted the optimal age for pneumococcal vaccination.

But first, let鈥檚 back up a bit.

Creating a 4-country cohort model

The investigators looked at 4 countries with 鈥渓ong-standing adult pneumococcal surveillance programs.鈥�² These included England (high income), Brazil (middle income), South Africa (middle income), and Malawi (low income), a country in southeast Africa.

The team found that the proportion of older adults between the ages of 55 and 65 was considerably higher in Brazil, Malawi, and South Africa than in England, as was the share of IPD.

For each country, here鈥檚 the proportion of adults in the 55-to-65 age group, followed by the percentage of annual cases of IPD:

• Brazil: 51.3%/44.5% (number of cases: n=186)
• Malawi: 51.0%/62.5% (n=4)
• South Africa: 53.8%/47.9% (n=134)
• England: 39.1%/19.9% (n=4657)

Considering this population data, it鈥檚 not surprising that the authors鈥� model identified a much younger optimal age for vaccination in the 3 lower- and middle-income countries (Brazil, Malawi, and South Africa) than in the 1 high-income country (England). 

Vaccine versus no vaccine

The international team of investigators also looked at the age at which the greatest proportion of IPD cases could be prevented, based on a scenario in which a 23-valent pneumococcal polysaccharide vaccine (PPV23) wanes rapidly, compared to a no-vaccine scenario. Here鈥檚 what they found:

• Brazil, age 55: 30.5% (proportion of preventable cases), 95% confidence interval [CI] 22.4% to 43.3%
• Malawi, age 55: 31.0%, 95% CI 7.7% to 96.6%
• South Africa, age 55: 20.0%, 95% CI 13.7% to 28.7%
• England, age 70: 13.7%, 95% CI 10.8% to 17.4%

Of particular note: While PPV23 was used in the above scenario, the cohort model predicted more preventable cases with 20-valent pneumococcal conjugate vaccine (PCV20).

Take the findings with a grain of salt

The authors urge 鈥渃autious鈥� interpretation of their findings, pointing to variations in the sensitivity of IPD surveillance. 鈥淩eported IPD case data in LMICs [low- and middle-income countries],鈥� they wrote, 鈥渁re usually incomplete or under-ascertained due to limited resources鈥攅.g., only 19 IPD cases were reported in Malawi and even less so when stratified by age and serotype.鈥�² 

Other possible limitations were cited, including the multiplicity of factors that can impact vaccine efficacy and the fact that the authors didn鈥檛 model sequential dosing of vaccine regimens.

Finally, the investigators predict that changes in infant vaccination schedules may reduce the benefit of adult vaccination targeting the same serotypes. 鈥淲ith the likely upcoming use of PCV15 and PCV20 in infants in the near future, the vaccine preventable fraction of adult disease is likely to diminish correspondingly because of the indirect effects of such infant program.鈥�²

Published: January 10, 2024