So far doctors have found twelve cases of whooping cough caused by pertussis bacteria that do not respond to pertussis vaccine.
All of the cases were discovered after analyzing the samples from children who had been hospitalized in Philadelphia in 2011 and 2012. The report added that the first ever cases of vaccine resistant whooping cough had been documented in Japan, France and Finland.
Experts are worried about the spread of the particular strain of the bacteria with over 18 fatalities due to whooping cough recorded in the United States since 1995. They also fear a return to the pre-vaccination era with more than 250,000 cases recorded during the 1930s compared to just over 42,000 cases recorded since 1995.