Kaiser Permanente tested diluted smallpox vaccine on 90 volunteers in a trial performed in California to determine if the vaccine could be spread among more patients. The researchers found that a one-fifth dilution was just as effective as the full-strength inoculation, suggesting that current smallpox vaccine stocks will inoculate significantly more patients than previously imagined. The findings suggest that every American could be vaccinated with existing supplies. None of the test subjects suffered serious side effects.