Pneumococcal serotype distribution in adults with invasive disease and in carrier children in Italy: Should we expect herd protection of adults through infants' vaccination?

Abstract

The 7-valent pneumococcal conjugate vaccine (PCV7) produced a significant herd protection in unvaccinated adult population mostly because of pneumococcus carriage decrease in vaccinated children. It is not known if the 13-valent pneumococcal vaccine can give similar effect on adults. Aims of the work were to evaluate whether the 6 additional serotypes are present in nasopharynx of children and serotype distribution in invasive pneumococcal infections (IPD) in adults. Realtime-PCR was used to evaluate pneumococcal serotypes in adults with confirmed IPD and in nasopharyngeal swabs (NP) from 629 children not vaccinated or vaccinated with PCV7 and resident in the same geographical areas. Two hundred twenty-one patients (116 males, median 67.9 years) with IPD were studied (pneumonia n = 103, meningitis n = 61 sepsis n = 50, other n = 7). Two hundred twelve were serotyped. The most frequent serotypes were 3, (31/212; 14.6%), 19A, (19/212; 9.0%), 12 (17/212; 8.0%), 7F, (14/212; 6.6%). In NP of children, the frequency of those serotypes causing over 50% of IPD in adults was very low, ranging from 0.48% for serotype 7F to 7.9% for serotype 19A. On the other side serotype 5, very frequent in NP (18.7%) caused <1% IPD. In conclusion serotypes causing IPD in adults are very rarely found in children NP. We suggest that herd protection obtainable with the additional 6 serotypes included in PCV13 may be more limited than that demonstrated with PCV7 in the past. In order to reduce the burden of disease in adults, adults should be offered a specific vaccination program with highly immunogenic PCV.

Other age groups than children need to be considered as carriers of Streptococcal pneumoniae serotypes

“…12,17 All these studies support the possible presence of a S. pneumoniae reservoir outside vaccinated children, an observation also made by other authors. 12,17,31 Non-PCV serotypes…”

“…However, this is not the case for some of the PCV serotypes when looking at the elderly in particular. 12,17 Studies have shown that there does not seem to be a hidden circulation of PCV serotypes carried in vaccinated infants, while PCV serotypes still contribute to IPD in unvaccinated individuals. 31 It has also been shown that some of the additional PCV-13 serotypes are still a major cause of IPD in the group of elderly persons, and that vaccination of children with PCV-13 has not shown a reduction in IPD with these serotypes in this age group.…”

Hospitalizations for pneumonia, invasive diseases and otitis in Tuscany (Italy), 2002-2014: Which was the impact of universal pneumococcal pediatric vaccination?

“…Similarly to our findings, other studies, performed in Wales and England, demonstrated that few years after PCV13 implementation a reduction of 32% of VT IPD was observed, but this decrease did not generate a high impact on the general pneumococcal disease incidence (VT and NVT) due to an increase of NVT diseases. 20,21 The increased incidence of pneumococcal disease could be related to the rise of the hospitalization rate observed in the older age groups (adult and the elderly), also demonstrated by Amodio at al., 17 for specified pneumococcal pneumonia and by Azzari e al., 23 revealing a progressive increase in the incidence of IPD in adults, particularly in the elderly, aged 61–75 y. Probably, the highest incidence of the disease in the elderly population must be related to a higher prevalence of co-morbidity in this subjects rather than in younger age groups and to the influence of other factors, such as lifestyle or confounding factors (eg, smoking prevalence in the general population, influenza vaccination coverage).…”

Pneumococcal Colonization in the Familial Context and Implications for Anti-Pneumococcal Immunization in Adults: Results from the BINOCOLO Project in Sicily

“…Studies on pneumococcal colonization in children have been widely undertaken [ 21 , 27 , 28 , 29 ]. However, the contribution of PCV immunized children to bacterial spread among their unvaccinated co-habiting relatives has not been investigated so far.…”

“…Several authors have reported that high rates of vaccination coverage in childhood may result in the herd immunity among unvaccinated subjects, protecting against disease caused by serotypes included in vaccine formulations [ 21 ], but also preventing nasopharyngeal colonization [ 22 ].…”