Pneumococcal vaccination uptake remains subpar in Singapore

Invasive pneumococcal diseases are more severe in elderly adults than in children, a recent Singapore study has found. There is a need to increase vaccination coverage in both populations.

“This is the first large-scale retrospective study investigating differences in pneumococcal disease and clinical outcomes between adult and paediatric populations in Singapore,” said researchers, noting that while vaccines in circulation cover majority of isolates from both adult and paediatric patients, vaccination rates remain low in the studied population.

Of the 889 patients included in the study, 63.1 percent were adults (n=561; median age, 62 years) and 36.9 percent were children (n=328; median age, 3 years). Only 16.5 percent (n=54) of children and 3.9 percent (n=22) of adults had received at least one dose of the appropriate vaccine at the time. The 23-valent polysaccharide conjugate vaccine (PPV23) was the most common (68.2 percent). [PLoS One 2019;14:e0220951]

The overall mortality rate was significantly higher in adults than in children (18.5 percent vs 3.1 percent; p≤0.001). Pneumonia was the leading cause of death in adults (24.2 percent) and meningitis in children (20 percent).

Multivariate logistic regression analysis found that being at least 65 years of age was a significant risk factor for pneumococcal disease mortality in adults (odds ratio, 2.5, 95 percent CI, 1.4–4.6; p=0.002). No such effect of age was seen for paediatric patients.

The introduction of PCVs affected the prevalence and composition of pneumococcal serotypes. Serotype 19A, for instance, increased by at least fivefold after the introduction of the vaccine in Singapore (adults: 1.6–5.6 percent; children: 4.5–20.8 percent).

This contradicts the medical literature, which found that the introduction of vaccines, especially in children, results in a drop in invasive pneumococcal disease rates. “[T]his has not been the case in Singapore, to our knowledge,” said the researchers, “as the majority of the cases described in this study were not vaccinated.”

The rise in serotype 19A prevalence after PCV introduction “is a great concern because we also found a high proportion of penicillin-nonsusceptible strains among this serotype,” they added. In particular, 79 percent and 35.4 percent of all isolates from children and adults, respectively, showed signs of resistance. Of the nonsusceptible isolates, 23 and 18 were of serotype 19A, respectively.

PCV7 covered serotypes responsible for 37 percent and 67 percent of adult and children invasive pneumococcal diseases, respectively. PCV13 covered an additional 25 percent of adult and 21 percent of paediatric cases, including serotype 19A.

“Although many of the main serotypes causing invasive disease were covered by the vaccines in use, it is imperative to continue vigilance for emergence of novel serotypes and development of vaccines with expanded coverage,” said the researchers.

“The high mortality rates in this study reflect an urgent need to increase vaccination coverage in both adults and children to tackle this vaccine-preventable infection,” they added.