WEDNESDAY, Nov. 7, 2007 (HealthDay News) -- Americans may be over-vaccinated against some diseases, according to a study that found the duration of protective immunity for many vaccines is greatly underestimated.
That means many people may be getting booster shots even though their immunity levels are adequate, the researchers say.
Based on the findings, it may be necessary to reevaluate timelines for vaccinating and revaccinating Americans against disease, said the Oregon Health & Science University researchers.
For this study, they analyzed 630 blood samples from 45 volunteers to determine each person's level of immunity against measles, mumps, rubella, chickenpox, mononucleosis, tetanus and diphtheria over an extended period of time.
"The goal of this study was to determine how long immunity could be maintained after infection or vaccination. We expected to see long-lived immunity following a viral infection and relatively short-lived immunity after vaccination, especially since this is the reasoning for requiring booster vaccinations," Mark Slifka, an associate scientist at the Vaccine and Gene Therapy Institute, said in a prepared statement.
"Surprisingly, we found that immunity following vaccination with tetanus and diphtheria was much more long-lived than anyone realized, and that antibody responses following viral infections were essentially maintained for life," he said.
The study is published in the Nov. 8 issue of the New England Journal of Medicine.
"We want to emphasize that proper vaccination is vital for protecting people against infectious disease. We also need to mention that over-vaccinating the population poses no health or safety concerns -- it may just be unnecessary under certain circumstances," said Slifka, who has joint appointments at the Oregon National Primate Research Center and the department of molecular microbiology and immunology in the OHSU School of Medicine.
"What our study found was that the life span of protective immunity for certain vaccines is much longer than previously thought. So, what does that mean? Based on this data and other studies, we may want to consider adjusting some of our recommended vaccination schedules," Slifka said. "Doing so may reduce the number of required shots that are administered each year in this country while at the same time help extend limited health care resources."
The U.S. Centers for Disease Control and Prevention has more about vaccines.