Does Serotype Replacement Erode the Benefits of Pneumococcal Vaccination?

Published - Written by John Staples

Picture this: You’re in your primary care office trying to convince a young mother to bring in her newborn for vaccinations in his second month. Sleep deprived and stressed, she says: “I know I should do it, doctor, but if it’s not one thing, it’s another. My eldest got the pneumonia vaccine a few years ago and still came down with pneumonia the following winter. Even if he’s vaccinated, won’t my youngest just catch something else?”

It turns out that this question isn’t just asked by exasperated mothers and vaccination skeptics. Many lines of evidence confirm that cases of pneumonia are reduced substantially soon after the initiation of pneumococcal vaccination programs, yet concerns remain that infections by nonvaccine serotypes might increase enough over time to obliterate these population-level benefits. Over the long term, are pneumococcal vaccination programs simply an exercise in futility?

In this week’s NEJM, Dr. Marie R Griffin (Vanderbilt University, Nashville) and colleagues address this question using the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) into the U.S. childhood immunization schedule in June 2000 as a natural experiment. Examining data on almost 18 million pneumonia-related hospitalizations from AHRQ’s Nationwide Inpatient Sample, the authors compared hospitalization rates in three epochs: Prior to the introduction of PCV7 (1997 – 1999), the early PCV7 years (2001 – 2006), and the late PCV7 years (2007 – 2009).

In what might come as cold comfort to an infant being jabbed with a needle, the authors found that pneumonia-related hospitalization rates in patients at the extremes of age (<4 and ≥65 years) were substantially reduced following the introduction of the PCV7 vaccine. Moreover, pneumonia-related hospitalization rates in these groups also fell between the early PCV7 years and the late PCV7 years, suggesting that the population-level benefits of vaccination weren’t simply countered by pneumococcal serotype replacement. Overall, the authors estimate that the introduction of the PCV7 vaccine resulted in 168,182 fewer U.S. hospitalizations in 2009 than would have been expected from the rate in the baseline years.

“No medical intervention is perfect, including the pneumococcal vaccination,” says NEJM Deputy Editor and Infectious Diseases specialist Dr Lindsey Baden, “However, this study offers evidence to physicians, policymakers, and parents that the introduction of the pneumococcal conjugate vaccination has produced substantial and sustained reductions in pneumonia-related hospitalizations at the population level.”

On a more personal level, you can reassure the young mother in your office of this: Pneumococcal vaccination will increase the likelihood that her son will remain healthy … hopefully making it more likely that she can catch some well-deserved rest.

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