Vaccines have prevented more than 103 million cases of communicable childhood diseases in the United States since 1924, including at least 26 million in the last decade alone, according to a study published last week in the New England Journal of Medicine.
The epidemiologists from the University of Pittsburgh who conducted the study say that they hope these statistics will help inform the public about the value of childhood vaccination programs — and the need to continue them.
“Low perceived risk at the individual level can lead to lower participation in control programs, with negative consequences for the entire community — a well-known game-theory principle that applies to vaccination programs as well,” they write.
In recent years, complacency and misinformed fears about vaccines has caused many parents to delay or refuse the vaccination of their children, a factor that is at least partly responsible for the rising and troubling incidence of measles and pertussis (whooping cough) outbreaks, the researchers point out.
“Organizing antivaccination movements amplify these problems,” they add.
A huge data set
For the study, the researchers took the unprecedented step of collecting and digitalizing all the weekly surveillance reports of nationally notifiable diseases for U.S. cities and states published between 1888 and 2011.
The reports include almost 88 million individual cases of 56 different diseases. For the NEJM study, however, the researchers focused on eight vaccine-preventable diseases: smallpox, polio, measles, rubella, mumps, hepatitis A, diphtheria and whooping cough.
The data gave the researchers a “quantitative history of each disease,” which they then used to estimate how many cases of the disease have been prevented since the introduction of its vaccine. (An estimate could not be made for smallpox, because of the lack of pre-vaccine data. The smallpox vaccine was introduced in the United States around 1800. The disease was essentially eradicated in the country by 1927, although outbreaks of a less severe variant of the virus continued until the late 1940s.)
The number of cases that were prevented by vaccines for each of the remaining seven diseases depended on two factors: how many people developed the disease before a vaccine became available, and 2) how long the vaccine has been in use.
Diptheria, for example, had the most cases prevented (about 40 million), but it had the second-highest pre-vaccination incidence rate (237 cases per 100,000 people per year) and its vaccine, which was developed in 1924, has been in use the longest.
The disease with the highest pre-vaccine incidence rate was measles (318 cases per 100,000 people per year). Its vaccine became available relatively recently — in 1963 — yet it’s prevented about 35 million cases of the disease, according to the study’s data. In fact, the effectiveness of the measles vaccine was remarkably swift. Five years after the vaccine was licensed, 95 percent of measles cases had been prevented.
That was a stunning achievement in public health — one that many people today fail to appreciate. As I’ve pointed out here before, in the pre-vaccine days, measles caused some 450 Americans (mostly children) to die and another 1,000 to suffer permanent brain damage or deafness each year.
Available to the public
With grant support from the Bill and Melinda Gates Foundation and the National Institutes of Health, the authors of the NEJM study have put all the data they gathered onto a website, where they hope it will provide “strong evidence of the value of vaccination programs.”
They’ve named their effort Project Tycho, after the 16th-century Danish astronomer Tycho Brahe, whose precise measurements of the movement of the planets was used by the German astronomer Johannes Kepler a century later to devise his laws of planetary motion.
The data on the website are broken down by region and state. Included is a 66-page preliminary report on Minnesota’s data.
Whether this remarkable collection of data will be enough to persuade all parents about the life-saving benefits of vaccines remains to be seen. The study’s authors, however, are hopeful.
“Lack of access to historical epidemiological data constrains scientific understanding of the dynamics of disease transmission, hampers disease-control programs, and limits public health education programs,” they write. “We believe that open access to large disease surveillance data sets in computable form should become a worldwide norm.”