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Surveillance data put researchers one step closer to group A streptococcal vaccine

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Findings from a seven-year surveillance program have given researchers a better understanding of geographic and temporal trends in group A streptococcal isolates that have important implications for the formulation of a multivalent type-specific vaccine.

Shulman et al monitored emm type distribution among 7,040 GAS pharyngitis isolates from 10 sites in the United States and 1,434 isolates from three sites in Canada. The emm gene encodes M protein, which is believed to play a role in type-specific immunity to GAS.

“We found that 85% of pharyngeal isolates are of emm types that are included in the experimental 26-valent M-protein vaccine,” the researchers wrote. “This exceeds the reported 79% of invasive U.S. GAS strains in a recent CDC study.”

Among the 56 emm types identified in the United States, the six most prevalent types in descending order were 1, 12, 28, 4, 3 and 2; types 12, 1, 28, 4, 3, 2 and 77 were the most prevalent among the 33 types identified in Canada.

These types account for 70% to 71% of isolates in each country, according to the researchers, and emm types 1, 12 and 28 are accountable for almost 50% of pharyngitis cases in each country.

However, emm type prevalence varied substantially each year depending on the geographic location.

“It is possible that increased levels of immunity to certain predominant types contributed to this variation, thus resulting in decreased prevalence of some of those types in subsequent years,” the researchers wrote. – by Nicole Blazek

Shulman S. Clin Infect Dis. http://www.journals.uchicago.edu/doi/abs/10.1086/599344

Dr. Shulman and colleagues have provided important data relating to emm types and the prospects for success with a multivalent GAS vaccine. However the past experience with a GAS vaccine where vaccinees developed rheumatic heart disease is a big hurdle to overcome for any M protein-based vaccine. There also is a concern that vaccination may quickly cause shifts in the dominant infecting strains of GAS just as the seven-valent pneumococcal conjugate vaccine has resulted in the emergence of previously uncommon pneumococcal strains. We need a GAS vaccine and these surveillance data are helpful.

Michael Pichichero, MD

University of Rochester Medical Center