On Aug. 17, 2003, Oregon Health & Science University (OHSU) announced the final results of a smallpox vaccine study that showed America’s preparedness for a smallpox outbreak may be greater than initially thought. The Research showed 90 percent of those vaccinated 25 to 75 years ago maintained a substantial level of immunity.

In addition, researchers concluded that in the long run, repeated vaccinations do not result in a higher level of disease protection. The research project was the largest of it’s kind ever conducted. The study was published in Nature Medicine.