Calculating vaccines’ impact
“Vaccine vindication” (SN: 1/25/14, p. 5) stated that vaccines have prevented 103 million cases of childhood diseases such as polio and rubella in the United States since 1924.
“How can the study assume there were so many cases of illness that were prevented?” asked Carolyn Bredenberg in an e-mail. “Were the data extrapolated from old data, or inferred from models based on old data, or what?”
Researchers looked at disease rates during prevaccine times and the increase in the U.S. population since then to estimate the number of illnesses that vaccines have prevented, explains departments editor Erika Engelhaupt. “The number of prevented cases is the difference between expected cases and actual cases,” she says. “Vaccines may actually have prevented even