Childhood vaccines prevent disease but risks remain
More than 103 million cases of serious childhood illnesses nationwide likely have been prevented by vaccines during the past century, researchers at the University of Pittsburgh Graduate School of Public Health announced on Wednesday after analyzing a first-of-its-kind database they developed.
The low incidence of diseases such as measles and pertussis, however, does not mean the risk of getting them is low, the researchers warned in a paper published in this week's New England Journal of Medicine.
“It's a dangerous proposition when people don't use a vaccine for a disease that can cause significant illness and death in children,” Dr. Donald S. Burke, the graduate school's dean and the paper's senior author, told the Tribune-Review. “That is going on all around the country right now — the perception that these diseases aren't coming any more. You do end up with pockets of parents who have decided not to immunize.”
The Pitt researchers orchestrated the first digitization of all national weekly U.S. surveillance reports of 56 reportable diseases between 1888 and 2011 as part of Project Tycho, which is named for a 16th-century Danish astronomer. Although the federal Centers for Disease Control and Prevention tracks cases of contagious diseases and issues a paper format, the data never had been assembled and made publicly available in an easy-to-use, digital format. The resulting database, consisting of more than 87 million reported individual cases, is now available for free at www.tycho.pitt.edu.
As part of Project Tycho, Pitt researchers used the assembled data to conduct a detailed analysis of eight diseases that can be prevented by vaccines: polio, measles, rubella, mumps, hepatitis A, diphtheria, smallpox and pertussis (also known as whooping cough).
The researchers estimated that 26 million cases of those diseases have been prevented in the past decade alone. Topping the list was diphtheria, a bacterial infection that is now extremely rare in the United States. Rates began to drop after a diphtheria vaccine was introduced in 1924.
Researchers were surprised that rates of diseases tied to modern vaccines such as polio and measles fell much faster than rates of older diseases such as diphtheria and pertussis.
Dr. Willem van Panhuis, the project's lead investigator, said vaccines were not consistently introduced across the country in the past, and vaccination programs lacked structure and clear-cut national guidelines.
“The stronger the program, it seems, the more rapidly a disease can be eliminated,” said van Panhuis, an assistant professor of epidemiology. “It's been demonstrated that if you have pockets of vaccine refusal, or pockets of lack of immunity, that can continue smoldering the transmission” of the disease.
The researchers singled out the intentional practice of “undervaccination,” which researchers said has contributed to recent outbreaks. For instance, a 2012 pertussis outbreak led to more than 38,000 cases of the illness nationwide, the worst epidemic since 1959.
Pitt began the project about four years ago as part of an effort to study why some diseases emerge in some places and not in others, the researchers said. Their computer-simulated projects were funded with grants from the Bill & Melinda Gates Foundation and the National Institutes of Health.
To base their studies on historical reality, Burke said, they began the labor-intensive task of pulling data sets from all over the country.
“We can do modeling, but we always want to verify it against historical examples.” Burke said. “Rather than choose an arbitrary time, we just said, ‘Let's go back to the beginning.' ”
The process of digitizing the data began in Cambodia, where students and workers manually entered the information as part of a contract with a nonprofit called Digital Divide Data. The organization trains them in developing countries and prepares them for jobs in the technology industry.
Pitt researchers plan to expand the database to include information such as vaccination rates, Burke said.
“We want to get better at predicting epidemics,” he said.
Luis Fábregas is a staff writer for Trib Total Media