BALTIMORE, Oct. 2 (UPI) -- Vaccine refusal contributed to the 2010 whooping cough spread of more than 9,000 cases in California, U.S. researchers said.
Jessica E. Atwell of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Josh Van Otterloo of Emory University School of Public Health in Atlanta and Jennifer Zipprich of the California Department of Public Health said the 2010 outbreak of pertussis, or whooping cough, of 9,120 cases was the largest whooping cough outbreak since 1947.