The dangerous synergism between influenza and Streptococcus pneumoniae and innovative perspectives of vaccine prevention.

Secondary bacterial pneumonia, particularly sustained by Streptococcus pneumoniae (Sp), represents an important cause of excess mortality during both influenza epidemics and pandemics. The lethal synergism between influenza virus and Sp was first suggested by studies performed on samples collected during autopsy from victims of 1918 influenza pandemic, and recently confirmed by data collected during the 2009 A/H1N1v influenza pandemic. Moreover, researches carried out in animal model contributed to partially clarify the pathogenic mechanisms underlying the synergism between these two etiological agents. Since 2000, a seven-valent pneumococcal conjugate vaccine (PCV7) was introduced in the US, and in the following year in Europe, determining substantial and almost immediate benefits in terms of reduction of invasive pneumococcal disease (IPD) in both vaccinated children and adults through induction of herd protection. Furthermore, several researches have recently demonstrated the capacity of the PCV7 to prevent community-acquired pneumonia (CAP) and, in particular, influenza-associated pneumonia hospitalisations among children. Taking into account the above-mentioned positive results obtained with PCV7, the availability of a new generation of conjugate pneumococcal vaccine with an enlarged antigenic spectrum (i.e. PCV13) offers promising perspectives, to improve the control of influenza through the protection offered against its major complications, particularly CAP, not only in children, but also among adults.