Potential coverage of a multivalent M protein-based group A streptococcal vaccine.

Background: The greatest burden of group A streptococcal (GAS) disease worldwide is due to acute rheumatic fever (ARF) and rheumatic heart disease (RHD). Safe, effective and affordable vaccines designed to prevent GAS infections that trigger ARF could reduce the overall global morbidity and mortality from RHD. The current study evaluated the potential coverage of a new 30-valent M protein-based vaccine using GAS isolates from school children in Bamako, Mali, a population at high risk for the development of RHD.

Methods: The bactericidal activity of rabbit antisera against the 30-valent vaccine was assessed using a collection of GAS isolates recovered during a study of the epidemiology of pharyngitis in Bamako.

Results: Single isolates representing 42 of 67 emm-types, accounting for 85% of the GAS infections during the study, were evaluated. All (14/14) of the vaccine emm-types in the collection were opsonized (bactericidal killing >50%) and 26/28 non-vaccine types were opsonized. Bactericidal activity was observed against 60% of the total emm-types recovered in Bamako, which accounted for 81% of all infections.

Conclusions: Multivalent vaccines comprised of N-terminal M peptides elicit bactericidal antibodies against a broad range of GAS serotypes, indicating that their efficacy may extend beyond the emm-types included in the vaccine.