We report an apparent association between the parental decision to decline pneumococcal immunization and the risk of hospitalization due to invasive pneumococcal disease or lobar pneumonia in children. Children of parents who declined pneumococcal vaccination were 6.5 times more likely to be hospitalized for clinically-defined pneumococcal disease than vaccinated children; the association was 10-fold in children without asthma.
PCV7 vaccination of young children is highly efficacious against invasive pneumococcal disease[31
], and moderately efficacious against radiograph-confirmed pneumonia and otitis media[21
]. PCV7 also decreases nasopharyngeal colonization of vaccine serotype pneumococci in both adults and unvaccinated children living with vaccinated household members[33
]. Routine PCV7 vaccination of infants in the US, as a consequence, has had a direct benefit for immunized children and indirect effect on reducing the overall incidence of pneumococcal-related disease in the general population[17
]. It is therefore likely that parents who decline PCV7 vaccination not only place their children at increased risk for pneumococcal disease, but may also increase the risk to the community.
Many parents report concerns about vaccine safety and some choose not to vaccinate their children[7
]. When compared to parents who accept vaccinations, parents who decline immunizations are more likely to believe their children are not at risk for vaccine-preventable diseases and that vaccine-preventable diseases are not dangerous[8
]. Results of this case-control study demonstrate that choosing to decline PCV7 immunization apparently places children at an increased risk for serious illness requiring hospitalization. We believe providers can use this information to help parents weigh the benefits and risks of immunizing their children.
Children diagnosed with asthma were 4 times more likely to be hospitalized for pneumococcal disease or lobar pneumonia than children without an asthma diagnosis. This finding is consistent with a study that showed a greater than 2-fold risk for invasive pneumococcal disease among persons ages 2 to 49 years with asthma[26
]. Although our study was not designed to examine the association between asthma and pneumococcal disease, this ancillary result further stresses the importance of maintaining high immunization rates to protect populations susceptible to severe illness.
This study has several limitations. It was conducted in a single managed health care plan in Colorado. While this may limit the generalizability of the findings, KPCO is an integrated health delivery system that represents the larger Colorado population. Colorado is an appropriate setting to study vaccine hesitancy because it is one of 21 states that allow personal belief exemptions to school immunization requirements, and has among the most lenient policies for obtaining personal exemptions[9
PCV7 serotypes have become increasingly rare over time, and a majority of invasive pneumococcal disease is now caused by non-PCV7 serotypes[15
]. This suggests that there may be alternative explanations for the high rate of probable pneumococcal disease in the cases whose parents declined vaccination. If the cases came from isolated communities, they would not benefit from the indirect effects of vaccination. However, all of these cases were KPCO members from across the greater Denver area. If the parents objected to traditional medicines, they may have delayed care until the illness became more serious. All of the cases, however, received regular outpatient care while enrolled at KPCO. In addition to these explanations, it is important to note that PCV7 serotypes are still present in the environment[34
], and most cases of lobar pneumonia are not confirmed microbiologically.
We used methods similar to other studies of pneumococcal morbidity and mortality to ascertain probable and proven cases of pneumococcal disease[21
]. In our study, 90% of the cases were identified as radiologically-confirmed lobar pneumonia. It is therefore likely that a proportion of these cases were caused by pathogens other than S. pneumoniae
or by non-PCV7 serotypes[21
]. Such misclassification of disease status likely occurred at a greater rate in the vaccinated case population for the following reasons: non-S. pneumoniae
-associated pneumonia would not be preventable by PCV7 vaccination, and rates of non-PCV7 serotype carriage are greater in vaccinated than unvaccinated populations[34
]. As shown in our sensitivity analyses, this differential misclassification of disease status would have biased the results to the null hypothesis. Despite this potential for negative bias, we found a statistically significant association between declining PCV7 vaccinations and the risk of hospitalization in children.
The decision to immunize can be difficult for some parents. It is important for physicians to clearly convey the benefits and risks of vaccination to help parents make informed decisions about protecting their children from infection. Physicians should also inform parents of the consequences associated with choosing not to vaccinate. As vaccine hesitancy continues to grow, future research should focus on developing effective risk communication messages that resonate with parents. Maintaining public trust in the US national immunization program is essential to the health of children and the community.