Comparison of Streptococcus pneumoniae nasopharyngeal colonization, serotype-specific and protein-specific antibody and cytokine levels in young children prior to, during and post COVID-19 pandemic.

Background: We studied changes in pneumococcal epidemiology and immunology in young children at pre-COVID, during-COVID and post-COVID time-frames.

Methods: Pneumococci were cultured from nasopharynx and density semi-quantified at six healthy child visits, age 6-36 months, and during acute otitis media (AOM). Serum antibody levels were measured by ELISA. Nasopharyngeal cytokine/chemokine levels were measured by rt-PCR. Differences between pre-COVID (2017 Mar-2019 July), during-COVID (2020 March-2022 March) and post-COVID (2022 April-2023 July) were analyzed.

Results: At healthy visits, pneumococcal detection was significantly lower during-COVID (21 %) vs. pre-COVID (28 %) and returned to 27 % post-COVID. Nasopharyngeal pneumococcal detection during AOM was not different during the three time frames (47-49 %), and density was consistently higher during AOM compared to healthy visits. Multiple vaccine and non- vaccine serotypes were detected during all time-frames. During-COVID, antibody levels to serotype 6A were lower than pre or post-COVID when measured at 24 months old. Increasing antibody levels occurred across the three time-frames for serotypes 22F and 33F. Pneumococcal- specific protein IgG levels did not differ across the three time-frames. Nasopharyngeal cytokine/chemokine levels during-COVID were lower.

Conclusions: During the COVID-19 pandemic pneumococcal nasopharyngeal colonization, antibody and cytokine levels in young children differed compared to before and after the pandemic.