The amount of protection that many vaccines offer is greatly underestimated and current vaccine schedules may need to be reevaluated, suggests new research in the New England Journal of Medicine.
The study, by Oregon Health & Science University researchers, finds that many people may be getting booster shots when their immunity levels may not require it.
The study's lead author, Dr. Mark Slifka, an associate scientist at the Vaccine and Gene Therapy Institute, notes that over-vaccinating the population poses no health or safety concerns; "it may just be unnecessary under certain circumstances."
The researchers evaluated blood samples from 45 study participants to determine the level of immunity in each individual for the flowing viruses:
- Measles
- Mumps
- Rubella
- Chickenpox (Varicella-zoster virus)
- Mononucleosis (Epstein-Barr virus)
- Tetanus
- Diphtheria
They expected to find that an infection with one of the viruses would provide long-lived immunity against it, while a vaccination against one of the viruses would provide relatively short-lived immunity, said Slifka.
"Surprisingly, we found that immunity following vaccination with tetanus and diphtheria was much more long-lived than anyone realized," said Slifka.
What's more, immunity following infections with measles, mumps, and rubella was maintained several decades and in most cases, for life.
The research also reconfirmed a previous finding by Slifka and his colleagues that the duration of immunity after smallpox vaccination is much longer than previously thought. They demonstrated in this study that antiviral antibody response is maintained with a calculated half-life of 92 years.
That's substantially longer than the current estimate proposed by experts at the U.S. Centers for Disease Control and Prevention of three to five years of immunity.
In the case of tetanus, doctors are told that vaccination is effective for 10 years, after which a booster shot is currently recommended. But the Slifka team found that once a person has received their primary series of vaccinations, they are likely to be protected for at least three decades.
Based on this data, Slifka's team suggests health authorities may want to consider adjusting some recommended vaccination schedules, to help extend limited health care resources.
He also notes his study does not diminish the need for vaccinations.
"We want to emphasize that proper vaccination is vital for protecting people against infectious disease," he said in a statement.
