Yale: Using a statistical method initially developed by Google, a Yale School of Public Health-led research team has devised a novel way to better analyze the impact of vaccines. The research was published in the Proceedings of the National Academy of Sciences. Pneumococcus, a bacterial pathogen, is one of the most significant causes of pneumonia around the world. According to the Centers for Disease Control and Prevention (CDC), pneumonia is the leading cause of death globally in children under the age of 5. Vaccines that prevent pneumococcal infection can decrease pneumonia rates, but quantifying the impact of the vaccine remains challenging.
A team led by Daniel Weinberger,
assistant professor in the Department of Epidemiology of Microbial
Diseases, used a method called “synthetic controls,” which was not
previously applied in an epidemiology context, to analyze the impact of
the pneumococcal vaccine. Created by Google to analyze web traffic, the
method allowed the team to separate changes in pneumonia rates caused by
the vaccine from other unrelated factors, providing a clearer picture
of the vaccine’s impact.
The idea to use a method from outside the
field of public health to analyze vaccine impact arose from a meeting
Weinberger attended at the World Health Organization (WHO). At the
meeting, “there was a discussion of how to adjust for changes in data
that are unrelated to the vaccine,” he said. To accomplish that, “we
felt we had to look outside the typical toolbox we were using.”
team began to explore approaches used to analyze data in other fields,
including economics and web analytics, and discovered a paper on
Google’s method of synthetic controls. They determined the method could
be applicable to vaccine evaluation.
The team examined pneumonia
hospitalization data from five countries: the United States, Brazil,
Chile, Ecuador, and Mexico. They found that the pneumococcal vaccine
significantly reduced pneumonia hospitalizations in young children,
and reduced hospitalizations for invasive pneumococcal disease and
pneumococcal pneumonia in children and adults. The team also found that,
in contrast to previous studies, the vaccine did not reduce pneumonia
hospitalizations for all causes in older adults in any of the five
countries following the introduction of the vaccine in children.
suggests that our understanding of which pathogens are causing
pneumonia in adults might not be exactly right,” said Weinberger.
“Pneumococcal strains targeted by the vaccine might be causing a smaller
fraction of pneumonia in that age group.”
Weinberger said that
the synthetic controls method could be useful in analyzing other public
health problems. Groups from the CDC and the Pan American Health
Organization have come to Yale to learn about the method and how to
apply it to other data sets. Weinberger is also working with the
Connecticut Emerging Infections Program, based at Yale, to apply this
method to their data on other diseases, such as influenza.
researchers on the project came from the Yale School of Public Health,
Yale School of Medicine, George Washington University, and Sage
Analytica. Yale collaborators include Christian Bruhn (lead author),
Esra Kurum, Joshua Warren, and Eugene Shapiro.