Evaluation of the impact of childhood 13-valent pneumococcal conjugate vaccine introduction on adult pneumonia in Ulaanbaatar, Mongolia: study protocol for an observational study

Abstract

Background Community-acquired pneumonia is an important cause of morbidity and mortality in adults. Approximately one-third of pneumonia cases can be attributed to the pneumococcus. Pneumococcal conjugate vaccines (PCVs) protect against colonisation with vaccine-type serotypes. The resulting decrease in transmission of vaccine serotypes leads to large indirect effects. There are limited data from developing countries demonstrating the impact of childhood PCV immunisation on adult pneumonia. There are also insufficient data available on the burden and severity of all-cause pneumonia and respiratory syncytial virus (RSV) in adults from low resource countries. There is currently no recommendation for adult pneumococcal vaccination with either pneumococcal polysaccharide vaccine or PCVs in Mongolia. We describe the protocol developed to evaluate the association between childhood 13-valent PCV (PCV13) vaccination and trends in adult pneumonia. Methods PCV13 was introduced into the routine childhood immunisation schedule in Mongolia in a phased manner from 2016. In March 2019 we initiated active hospital-based surveillance for adult pneumonia, with the primary objective of evaluating trends in severe hospitalised clinical pneumonia incidence in adults 18 years and older in four districts of Ulaanbaatar. Secondary objectives include measuring the association between PCV13 introduction and trends in all clinically-defined pneumonia, radiologically-confirmed pneumonia, nasopharyngeal carriage of S. pneumoniae and pneumonia associated with RSV or influenza. Clinical questionnaires, nasopharyngeal swabs, urine samples and chest radiographs were collected from enrolled patients. Retrospective administrative and clinical data were collected for all respiratory disease-related admissions from January 2015 to February 2019. Discussion Establishing a robust adult surveillance system may be an important component of monitoring the indirect impact of PCVs within a country. Monitoring indirect impact of childhood PCV13 vaccination on adult pneumonia provides additional data on the full public health impact of the vaccine, which has implications for vaccine efficiency and cost-effectiveness. Adult surveillance in Mongolia will contribute to the limited evidence available on the burden of pneumococcal pneumonia among adults in low- and middle-income countries, particularly in the Asia-Pacific region. In addition, it is one of the few examples of implementing prospective, population-based pneumonia surveillance to evaluate the indirect impact of PCVs in a resource-limited setting.

Epidemiology of pneumonia in hospitalized adults ≥18 years old in four districts of Ulaanbaatar, Mongolia, 2015–2019

“…17 Surveillance data were collected both retrospectively (January 2015−February 2019) and prospectively (March 2019−March 2022). 19 For the purposes of this analysis, only retrospective data were included.…”

“…Clinical pneumonia was defined as a patient who was diagnosed with community-acquired pneumonia at both admission and at time of discharge, and with two or more of the following symptoms (at least one of which must be respiratory): 7 , 19 reported fever or measured fever (≥38·0°C) new cough or change in chronic cough new or increased sputum production leucocytosis (>11·0 × 10 9 white blood cells/l) or leukopenia (<4·0 × 10 9 white blood cells/l) dyspnoea or tachypnoea (i.e., difficult breathing or respiratory rate >25 breaths/minute) lung findings on auscultation hypoxaemia (oxygen saturation <90%) pleuritic chest pain …”

“…Severe clinical pneumonia was defined as clinical pneumonia with 1) an ICU admission, 2) death during hospital stay, or 3) clinical pneumonia with two or more of the following symptoms: 19 , 20 impaired conscious state (Glasgow coma scale <15) respiratory rate of ≥30 breaths per minute hypotension (systolic blood pressure ≤90 mmHg or diastolic blood pressure ≤60 mmHg) hypoxaemia …”

“…Clinical pneumonia was defined as a patient who was diagnosed with community-acquired pneumonia at both admission and at time of discharge, and with two or more of the following symptoms (at least one of which must be respiratory): 7,19 reported fever or measured fever (≥38¢0°C) new cough or change in chronic cough new or increased sputum production leucocytosis (>11¢0 £ 10 9 white blood cells/l) or leukopenia (<4¢0 £ 10 9 white blood cells/l) dyspnoea or tachypnoea (i.e., difficult breathing or respiratory rate >25 breaths/minute) lung findings on auscultation hypoxaemia (oxygen saturation <90%) pleuritic chest pain Severe clinical pneumonia was defined as clinical pneumonia with 1) an ICU admission, 2) death during hospital stay, or 3) clinical pneumonia with two or more of the following symptoms: 19,20 impaired conscious state (Glasgow coma scale <15) respiratory rate of ≥30 breaths per minute hypotension (systolic blood pressure ≤90 mmHg or diastolic blood pressure ≤60 mmHg) hypoxaemia Patients that met the case definition criteria were included in the study. Staff extracted relevant clinical data from patient medical charts, including clinical presentation at admission and case management, age, underlying medical conditions, and clinical outcomes.…”

“… 18 A subsequent adult surveillance program was established in 2019, as part of a larger study aiming to determine the indirect effect of childhood PCV13 on community-acquired pneumonia in adults. 19 To quantify the burden of adult community-acquired pneumonia in Ulaanbaatar, hospital-based surveillance was initiated in four districts of the city. Our study aims to establish the burden and clinical characteristics of community-acquired pneumonia in adults 18 years or older in Mongolia.…”