In September 2009, news stories reported that researchers in Canada had found an increased risk of pandemic H1N1 (pH1N1) influenza in people who had previously been vaccinated against seasonal influenza. Their research, consisting of four different studies, has now undergone further scientific peer review and is published in the open access journal PLoS Medicine.
In a school outbreak of pH1N1 in spring 2009, people with cough and fever were found to have received prior seasonal flu vaccination more often than those without.
Several public health agencies in Canada therefore undertook four additional studies during the summer of 2009 to investigate further. Taken together, the four studies included approximately 2,700 people with and without pH1N1.
The first of the studies found the seasonal vaccine to be associated with an increased risk of approximately 68 percent for pH1N1 disease. The further 3 studies similarly found between 1.4 and 1.5 times increased likelihood of pH1N1 illness in people who had received the seasonal vaccine compared to those who had not.
The World Health Organization conceded shortcomings in its handling of the H1N1 swine flu pandemic, including a failure to communicate uncertainties about the new virus as it swept around the globe, Reuters reported.
WHO’s six-phase system for declaring a pandemic had sown confusion about the flu bug which was ultimately not as deadly as the widely-feared avian influenza.
[Source]
Chapter: Vaccines :: 11 August 2010
