Since 1924, vaccines have prevented more than 103 million cases of eight contagious diseases in the U.S., researchers reported.
And in the past decade alone, immunization has prevented 26 million cases of disease -- 99% of those that would have otherwise occurred, according to Willem van Panhuis, MD, PhD, of the University of Pittsburgh Graduate School of Public Health, and colleagues.
The findings come from analysis of a new database that includes all weekly surveillance reports of nationally notifiable diseases for U.S. cities and states published between 1888 and 2011, Van Panhuis and colleagues reported in the Nov. 28 issue of the New England Journal of Medicine.
The data set includes 87,950,807 individual cases, each of them pinned down to a time and place, the researchers said, and will be publicly available for study.
It took some 200 million keystrokes to put the data in digital form, the researchers reported. All told, 56 diseases were reported for some of the time between 1888 and 2011, but no single illness was reported continuously, they wrote.
The database was dubbed Project Tycho, after the astronomer Tycho Brahe, whose painstaking observations of the skies supplied the raw data that led to the development of the laws of planetary motion.
Similarly, Van Panhuis and colleagues argued, the new data set will allow better "interpretation of long-term disease patterns."
As an illustration, they tracked the effect of vaccines on eight major communicable diseases, all now preventable by vaccination.
"Using this database, we estimate that more than 100 million cases of serious childhood contagious diseases have been prevented, thanks to the introduction of vaccines," Van Panhuis said in a statement.
"But we also are able to see a resurgence of some of these diseases in the past several decades as people forget how devastating they can be and start refusing vaccines," he added.
"Analyzing historical epidemiological data can reveal patterns that help us understand how infectious diseases spread and what interventions have been most effective," commented Irene Eckstrand, PhD, of the National Institute of General Medical Sciences.
The analysis of the vaccine effects "shows the value of using computational methods to study historical data," Eckstrand said in a statement.
The General Medical Sciences institute was one of the sponsors of the project, along with the Bill & Melinda Gates Foundation.
Raw material for the data set came from the CDC's Morbidity and Mortality Weekly Report, as well as its precursors, the researchers reported.
The eight diseases analyzed in the journal are smallpox, measles, polio, rubella, mumps, hepatitis A, diphtheria, and pertussis.
For the last seven, the researchers compared incidence rates before and after licensure of the vaccine to estimate how many cases have been prevented.
For smallpox, though, there was no data from the era before the 1800 introduction of the vaccine, so it was not possible to pin down the number of prevented cases.
Nonetheless, the data show a consistent decline in smallpox over time, with severe disease caused by variola major eliminated by 1927, but epidemics of variola minor continued until the late 1940s, the researchers reported.
For the other seven, the licensing of the appropriate vaccine marked declines in incidence that were more or less rapid. For instance, in the case of diphtheria toxin, antitoxin was available starting around 1914, but there were yearly epidemics until 1924, when heat-inactivated diphtheria toxoid was introduced.
Diphtheria topped the list of cases prevented by vaccination -- some 40 million -- because the pre-vaccine incidence was high, at 237 cases per 100,000 population per year, and the vaccine was one of the first introduced.
Measles had the highest pre-vaccine incidence rate, at 318 cases per 100,000 population per year, and an estimated 35 million cases have been prevented, although the vaccine was only introduced in 1963.
The measles vaccine had the most rapid effect, with 22.5% increases in the number of prevented cases in each of the first 5 years after it was licensed.
By year five, Van Panhuis and colleagues reported, 95% of expected measles cases had been prevented. In contrast, reaching that level took 19 years for diphtheria and 17 for pertussis, they wrote, "presumably owing to much slower vaccine rollouts in a different era."
Despite the success of vaccines, they noted, the U.S. has seen "multiple resurgences" of measles, rubella, mumps, and pertussis since the 1980s, probably because of gaps in vaccine coverage that disrupt herd immunity.
The database project had support from the Bill & Melinda Gates Foundation and the NIH. Aside from grants from those organizations, the authors made no disclosures.
New England Journal of MedicineSource Reference:
Van Panhuis WG, et al "Contagious diseases in the United States from 1888 to the present" N Engl J Med 369; 22: 2152-2158.