In the 2008/9 winter season, at the beginning of the 2009 pandemic (H1N1) flu season, Canadian researchers started noticing that people who received a flu shot seemed more likely to catch the flu than those who had not taken a flu shot. Five studies across the country that year showed the same results, indicates CBC
. As a result of the study findings, Quebec opted not the offer the flu vaccine. But research outside Canada at the time did not show any similar problems, so the Canadian findings were easily dismissed and rejected. It was thought to be just a 'Canadian problem.'
But now a new study, presented Sunday at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), suggests the Canadian findings may have been real, says The Globe and Mail
. Researchers from the B.C. Centre for Disease Control in Vancouver recreated the event in ferrets because it would have been unethical to conduct this study on humans. Ferrets are the best animal models for studying the flu and predicting how it will act in humans.
The researchers gave 16 ferrets the 2008 flu shot and another 16 ferrets a placebo shot, says The Vancouver Sun
. The study was blinded, meaning researchers didn't know which ferrets were given which shot. Then all the ferrets were exposed to the H1N1 virus. The vaccinated ferrets became significantly more ill than the other animals. Eventually, all ferrets recovered.
The researchers also mentioned that in the time since 2009, other countries have noticed similar interactions. They said it is important to figure out what happened, before the next pandemic occurs. While seasonal flu occurs every year and is substantially protected against with the seasonal flu vaccine, pandemic flu is rare. Researchers need to determine whether the B.C. findings were unique to the pandemic.
There are a few theories explaining why the pandemic flu vaccine might not have protected properly against H1N1. The one favoured by the B.C. researchers is that the 2008/9 vaccine protected against a virus that was related to H1N1 but was not similar enough to it. Thus, it could not generate the antibodies needed to neutralize it. This theory suggests the vaccine may have actually facilitated infection with the pandemic virus.