Vanderbilt Study Shows Childhood Immunization with Pneumococcal Conjugate Vaccine Cuts Pneumonia Hospital Admissions in the US

Routine infant immunization with pneumococcal conjugate vaccine (PCV7) has caused a 39 percent fall in all-cause pneumonia hospital admission rates for American children under 2, according to an article published in this week’s edition of The Lancet. Carlos G. Grijalva, M.D., M.P.H., research assistant professor in Vanderbilt’s Department of Preventive Medicine, along with colleagues in the Vanderbilt University School of Medicine and the Centers for Disease Control and Prevention (CDC) in Atlanta, used data from the Nationwide Inpatient Sample – the largest inpatient database available – to carry out their study. Pneumonia and influenza combined are the greatest infectious cause of death in the U.S., and pneumonia accounts for between 3 and 18 percent of all childhood hospital admissions. The research team looked at all-cause pneumonia hospital admissions for two periods — between 1997 and 1999, and between 2001 and 2004. The year 2000 was omitted from the study, as this was the year the vaccine was introduced – and due to variable rates of uptake across the USA it was decided this year should not be included. They found that rates of all-cause pneumonia hospital admissions for the post vaccination years fell by 506 cases per 100,000 children under 2 – a drop of 39 percent, and representing an actual reduction of some 41,000 admissions in 2004. The study also provided evidence of the so-called “herd immunity effect” – in which unvaccinated older people benefit from the vaccination of children and infants.
In this case, the 41,000 reduction in hospital admissions for all-cause pneumonia in children under 2 was accompanied by an annual decline of nearly 25,000 hospital admissions in adults, 18-39. The study notes that one explanation of this could be that this age group includes parents of young children, who may have benefited from reduced exposure since their children had been vaccinated.
“Our results contribute to the growing body of evidence supporting the beneficial effects of the pneumococcal conjugate vaccines in children,” Grijalva said. “The introduction of the vaccine could have a large effect in less developed countries, where pneumococcal diseases cause not only substantial morbidity and health care costs but also high childhood mortality.”
In an accompanying comment Orin Levine of the Johns Hopkins Bloomberg School of Public Health, Baltimore, and Felicity Cutts of the London School of Hygiene and Tropical Medicine, London, said: “These findings are important because, in cost-effectiveness studies done before the launch of the vaccine – and based on clinical trial data – the estimated economic benefits of vaccination were limited to health impacts in vaccinated children. The reduction in all-cause pneumonia in vaccinated and unvaccinated populations illustrates how the value of the vaccine has far exceeded expectations.”