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Streptococcus pneumoniae (S. pneumoniae) causes a large proportion of community-acquired pneumonia cases in Japan. Exploring the national impact of recently developed pneumococcal conjugate vaccines (PCVs), a new study published in Vaccine reports the serotype distribution and clinical characteristics of adult pneumococcal pneumonia between 2011 and 2020.¹

Maeda and colleagues included 2 multicenter observational studies conducted in Japan, evaluating trends over 3 time periods before and after the introduction of pediatric PCVs. A total of 650 patients were enrolled, who were a median age of 73 years. In this cohort, 59.7% of patients were male, 86.9% had comorbidities, and 10.2% were nursing-home residents.

Is what鈥檚 good for kids also good for adults?

Following the country鈥檚 2013 rollout of the 13-valent PCV (PCV13) for children, rates of pneumococcal pneumonia caused by PCV serotypes subsided among adults. PCV13 serotypes fell from 52.7% in 2011鈥�2014 to 30.4% in 2016鈥�2017 (P<.001), possibly an indirect result of less infection among children. Of note, the proportion of PCV13 serotypes in adult pneumococcal pneumonia has been stable since 2017. 鈥淗owever, PCV13, PCV15, and PCV20 serotypes still accounted for 38.5%, 43.3%, and 59.6% of total pneumococcal pneumonia in 2018鈥�2020, respectively,鈥� the authors noted.¹

The reduction in PCV13 serotypes observed in the present study varied by host. The decline was more pronounced in patients ages 65 and older (-23.5%; P<.001) than in those younger than 65 (-12.3%; P=.104) during 2 of the time periods studied (2011鈥�2014 and 2016鈥�2020). Variability was also greater in women than in men (-29.7% versus -13.8%), though this difference did not reach statistical significance. The authors noted the possibility that women may have more contact with children, allowing similar serotypes to pass between the 2 groups. This finding aligns with a U.S. study, which concluded that after winter holidays, invasive pneumococcal diseases (IPD) caused by serotypes common in children increased among older adults, particularly older women.²

Based on their data, Maeda and colleagues also theorize that introducing PCVs to older adults may help curb pneumococcal pneumonia spread in general.¹ From 2018 to 2020, the ratios of PCV15 and PCV20 serotypes were, ultimately, very similar to those seen in adults 65 years and older.

鈥淭hese results indicate that introducing PCVs, including newly developed PCVs, to older adults aged 鈮�65 years could prevent additional pneumococcal pneumonia cases in adults,鈥� the authors reported.¹

A catalyst for updated vaccination policies

The overall abatement of PCV13 serotypes observed during the study period was for the most part due to declines in serotypes 3, 19F, and 14. The proportion of serotype 3 in particular has decreased, from 22.7% to 10.3% (P<.001), since the introduction of pediatric PCV13. However, serotype 3 is still dominant, having increased in both IPD and pneumococcal pneumonia cases, pediatric vaccines notwithstanding. On the other hand, the proportion of PPSV23 non-PCV serotypes stayed the same during the study period, though they were less frequent in the PPSV23-vaccinated group than in the nonvaccinated group.

The severity of pneumococcal pneumonia waned over time, which is notable because rates of vaccination against PPSV23 actually went down during the study period. This dwindling of disease acuity may be due to the aforementioned reduction in serotypes 3 and 19F, which are associated with severe disease.

鈥淏ased on our data, it is time to consider the next Japanese pneumococcal vaccination policy for older adults,鈥� the authors wrote, calling for additional studies.¹ They also pointed out that, as serotypes differ by geographical area, local data are needed to design future immunization programs.

Published: January 30, 2023