Pilishvili T et al. Pediatrics 2010; 126: 9-17

With this case-control study the authors evaluated risk factors for invasive pneumococcal disease (IPD) among children who were aged 3 to 59 months in the era of pneumococcal conjugate vaccine (PCV7). IPD cases were identified through routine surveillance during 2001-2004. They matched a median of 3 control subjects to each case patient by age and zip code. 782 case patients (45% vaccine-type IPD) and 2512 matched control subjects were enrolled. They calculated odds ratios for potential risk factors for vaccine-type and non-vaccine-type IPD by using multivariable conditional logistic regression. Among children who received any PCV7, there was an increased risk for vaccine-type IPD when they had underlying illnesses, were male, or had no health care coverage. Vaccination with PCV7 did not influence the risk for non-vaccine-type IPD. Presence of underlying illnesses increased the risk for non-vaccine-type IPD, particularly among children who were not exposed to household smoking. Non-vaccine-type case patients were more likely than control subjects to attend group child care, be male, live in low-income households, or have asthma; case patients were less likely than control subjects to live in households with other children.

Funding was provided by CDC’s Antimicrobial Resistance Working Group, the CDC’s Emerging Infections Program and the National Vaccine Program Office. Two of the authors have received honoraria from various vaccine manufacturers, but none related to this work. All other authors declared no conflict of interest.

ECDC comment:

In recent years a large number of European countries have implemented routine PCV7 childhood immunization. After PCV7 introduction, a large impact on the epidemiology of IPD and a natural variation in pneumococcal serotype distribution has been observed. As demonstrated by the same authors in another observational study the reductions in overall IPD resulted from a 99% decrease in disease caused by the seven vaccine serotypes. Therefore, vaccination with PCV7 is an effective tool for reducing the risk for vaccine-type IPD even more among children with traditional risk factors. Since these factors are still associated with non-vaccine-type IPD risk, it is important to continue following the serotype distribution to assess the possible replacement with the new licensed conjugate vaccines.