Pneumococcal infection and its vaccine control

Pneumococcal infection is caused by more than 100 serotypes of S. pneumoniae (Spn), as well as non-encapsulated pneumococci. The greatest danger is posed by invasive pneumococcal infections (IPI), when the pathogen is found in locations that should be sterile. IPI most often includes meningitis and septic conditions. Spn caused between 929,000 and 1.4 million deaths worldwide only in 2019. The widespread use of pneumococcal conjugate vaccines (PCVs) for children in vaccination programs has significantly influenced the epidemiological process of this infection, gradually leading to a decrease in the effectiveness of PCVs and accompanied by an increase in the number of Spn serotypes in PCVs due to previously non-vaccinal serotypes (NVST), which became invasive and relevant in the process of expanding the scope of vaccination. The aim of the study was to analyze changes in the invasiveness of Spn from different serotypes against the background of vaccination, the evolution of PCVs, and the prospects for vaccine control of pneumococcal infection. The paper provides an analysis of literature data on the high efficacy of PCVs against IPI caused by vaccine serotypes (VST) Spn, the gradual serotype change of invasive Spn and their acquisition of epidemic relevance, multidrug resistance; risks associated with nonencapsulated Spn; dynamics of increasing valency of PCV serotypes (from PCV7 to PCV21, development of PCV24, PCV25, and PCV31) and their further impact on the epidemic process in different countries and regions of the world. The impact of vaccination on the composition of the upper respiratory tract microbiome was discussed, as well as differences in IPI levels in different territories and their causes. It was demonstrated that vaccination against pneumococcal infection does not provide a warranty of protection even against fatal cases due to the acquisition of highly invasive properties by NVST. The use of PCVs does not adequately affect the intensity of circulation of some VSTs (types 3 and 19A). The dynamics of IPI levels (2010–2022) and changes in the dominant Spn serotypes were analyzed using the example of EU/EEA countries. In 17 (63%) of 27 countries, there was a tendency for IPI to increase against the backdrop of long-term vaccination; in 3 (11%), there was a stable trend; in 7 (26%), there was a decline in morbidity. However, even with a downward trend, the IPI levels in some countries exceeded those in some countries where an upward trend was observed. The total IPI cases for these countries did not actually decrease and ranged from 5.7 to 6.4 per 100,000 population, with a moderate upward trend. The results of our analysis show that the widespread use of PCVs, even with an increase in their valence, will require constant replacement of current serotypes, without actually significantly affecting IPI levels. This does not allow us to talk about vaccine control of IPI either now or in the future. We see the only optimal solution for curbing the accelerated artificial evolution of Spn, stabilizing the epidemic process, and optimizing the use of PCVs as directing the vaccination strategy toward medical and epidemic risk groups.