Routine infant immunisation with pneumococcal conjugate vaccine (PCV7) has caused a 39% fall in all-cause pneumonia hospital admission rates for American children aged under two years, according to an article published in this week's edition of The Lancet.
Dr Carlos G. Grijalva and colleagues at the Vanderbilt University School of Medicine, Nashville, Tennessee, USA, and the Centres for Disease Control and Prevention (CDC), Atlanta, Georgia, USA, used data from the Nationwide Inpatient Sample – the largest inpatient database available in America – to carry out their study.
In the USA, pneumonia and influenza combined are the greatest infectious cause of death, accounting for between three and 18% 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 culminating in variable rates of uptake across the USA.
They found that rates of all-cause pneumonia hospital admissions for the post vaccination years fell by 506 cases per 100,000 children under two years – 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 people outside the target range of the study 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 two was accompanied by an annual decline of nearly 25,000 pneumonia hospitalisations in adults aged 18-39. The study notes that one cause 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.
The authors conclude: "Our results contribute to the growing body of evidence supporting the beneficial effects of the pneumococcal conjugate vaccines in children.
"The introduction of the vaccine could have a large effect in less developed countries, where pneumococcal diseases cause not only substantial morbidity and healthcare 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, 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."
Journal
The Lancet