Pre- & post-vaccine trends in pneumococcal serotypes & antimicrobial resistance patterns

Background & objectives The Pneumococcal vaccines were introduced under the Universal Immunization Programme (UIP) in 2021 in India. Drawing from the collective experience of various nations, it is anticipated that there will be a substantial shift in serotype patterns following the introduction of this vaccine. The available data is limited to years until 2018 when the vaccine was introduced in only five States. The present study was carried out to estimate the changes in serotypes and antimicrobial resistance patterns pre- and post-vaccine introduction from a tertiary care centre. Methods All isolates from various clinical specimens in the pre-vaccine era (January 2015-July 2021, except for 2019) and post-vaccine era (August 2021- March 2023) were included. Antimicrobial susceptibility was tested using disc diffusion or VITEK2, and serotyping was performed using the Quellung test (post-vaccine introduction) or sequential multiplex PCR (pre-vaccine introduction). The Chi-square or Fisher exact test was used to identify associations between antimicrobial resistance and serotypes. The z-test for proportions was used to identify significant changes in serotype frequencies between the pre- and post-vaccine era; P<0.05 was considered as the level of significance. Results Overall, the resistance rates increased for most of the antibiotics in the post-vaccine era, and there was no significant increase in the non-vaccine serotypes. The proportion of serotypes 19F and 15B/C increased, and serotypes 23F and 14 reduced in the post-vaccine era. The majority of the 19F and 19A isolates (89.7% and 80%, respectively) were multidrug resistant in the post-vaccine era. Interpretation & conclusions Introducing pneumococcal vaccination reduced the burden of many vaccine serotypes, while the burden of non-vaccine serotypes slightly increased. Most of the vaccine serotypes (like 19F and 19A) that persisted in the post-vaccine era were drug resistant.