Memory B cell responses induced by pneumococcal conjugate vaccine schedules with fewer doses: analysis of a randomised-controlled trial in Viet Nam.

The use of pneumococcal conjugate vaccine (PCV) schedules with fewer doses are being considered to reduce costs and improve access, particularly in low- and middle-income countries. While several studies have assessed their immunogenicity, there are limited data on their potential for long-term immune protection, as assessed by pneumococcal serotype-specific memory B cell (B mem ) responses. This current study reports secondary outcome data that aims to compare B mem responses following reduced-dose (0 + 1 and 1 + 1) schedules of PCV10 and PCV13 in Vietnamese infants from our randomised-controlled trial (trial registration number NCT03098628). Following vaccination at 12 months of age, B mem levels for most serotypes peaked seven days post-vaccination and were higher in magnitude for the 1 + 1 than 0 + 1 schedules and for PCV13 than PCV10. Furthermore, B mem did not wane as rapidly as IgG levels by 24 months of age. Further studies are needed to assess the use of B mem as markers of long-term protection against pneumococcal carriage and disease, which is crucial to generate data for immunisation program decision-making.