# 3779
A hat tip to Crof over at Crofsblog who has word of a press release from the British Columbia Centre For Disease Control, which outlines their strategy for seasonal and pandemic vaccinations this fall in light of what has become known as the `The Canadian Problem’.
The `Canadian Problem’ is the as-yet unpublished study that is widely reported to suggest that people who received a seasonal flu shot last year were twice as likely to contract the pandemic flu strain this past spring.
The CDC here in the US says they have seen no evidence in their data to support this assertion, but `would obviously like to see the data’.
Since we’ve not seen the Canadian study, I’ve no idea what the authors are suggesting as the cause of this phenomenon.
That said, there is an immunological concept (and I’m admittedly wandering into pretty speculative territory here) known as `Original Antigenic Sin’ (a term coined in 1960 by Thomas Francis, Jr. in the article On the Doctrine of Original Antigenic Sin) that might - at least theoretically – serve as a plausible way this could come about.
In Original Antigenic Sin, when the body’s immune system is exposed to and develops an immunological memory to one virus, it may be less able to mount a defense against a subsequent exposure to a second slightly different version of the virus.
Original Antigenic sin has been described in relation to influenza viruses, Dengue Fever, and HIV. Whether it plays any part in `The Canadian Problem’, or whether that `problem’ even exists at all, is something we will have to wait to see.
Obviously this is fascinating stuff for us disease geeks (and we eagerly await more information), but for the average citizen, it comes down to a more basic question.
Does getting the seasonal vaccine increase your chances of getting the swine flu? And if so, how much?
Unfortunately, we don’t have the answer to that question yet.
Here in the US, the CDC has so far downplayed these reports. The WHO, and other health agencies around the world, are looking to see if they can find anything in their data to corroborate these (as yet, unpublished) findings.
So far, they say they can’t.
In Canada, over the past few days, several provinces – including Quebec, Alberta, Ontario, and Nova Scotia – announced they were making adjustments to their seasonal flu vaccination campaign.
British Columbia today has followed suit. Partially, they say, to enable Health Care Providers more time to concentrate on delivering the H1N1 pandemic vaccine when it becomes available in November, but also clearly in response to this study.
Whether this ends up being a prudent move, or an over-reaction, is something we may not be able to figure out for weeks or months.
Here is the B.C. Centre for Disease Control Press release.
NEWS RELEASE
For Immediate Release
2009HLS0023-000414September 28, 2009
Ministry of Healthy Living and Sport
BC Centre for Disease Control
TARGETED VACCINE CAMPAIGN WILL PROTECT THOSE AT RISK
VICTORIA – B.C.’s seasonal flu vaccine campaign will focus first on those at highest risk for seasonal flu and be followed closely by the H1N1 flu vaccine that will be available to everyone who needs and wants it, announced Minister of Healthy Living and Sport Ida Chong with provincial health officer Dr. Perry Kendall.
“Delivering the vaccine campaign in this fashion allows us to best protect British Columbians most at risk from seasonal flu, while still ensuring that everyone who needs and wants the H1N1 flu vaccine will be able to receive it as soon as it’s available,” said Kendall. “By initially targeting the seasonal flu campaign to those at highest risk, it not only removes a number of logistical challenges that come with trying to run two full immunization programs at once, but it is also in the best public health interest of British Columbians.”
On October 13, the seasonal flu vaccine will be offered to people 65 and older, and residents in long-term care homes. A pneumococcal vaccine will also be available at the same time for high-risk individuals (seniors and those with chronic medical conditions) to prevent influenza-related pneumonia.
“This is a decision that has not been taken lightly,” said Chong. “It has been assisted by independent ethical review and has undergone thoughtful review and deliberation by public health officials, scientists and policy makers in B.C. and across Canada over the past several weeks.”
Starting in November, the H1N1 flu vaccine will be rolled out and will be available to everyone who needs and wants it. Then, in early 2010, the seasonal flu vaccine will once again be offered to everyone else under the age of 65 according to the usual guidelines.
“This year, the predominant strain of seasonal influenza is, in fact, the pandemic H1N1 virus,” said Dr. David Patrick, epidemiology services director at the BC Centre for Disease Control. “While those people who are 65 and older and who live in long-term care homes should still receive the seasonal flu shot, for the majority of the population, the flu virus they need to protect themselves against is this strain of H1N1.”
The decision to focus the flu vaccine campaign in this way was based on a number of reasons, including:
· The possibility of an early fall second wave of H1N1 flu.
· The timing of H1N1 vaccine availability.
· The strains of influenza that are currently circulating.
· Canadian research that has suggested a potential association between prior seasonal influenza vaccination and the risk of acquiring pandemic H1N1 disease.
For more information on the seasonal flu vaccine, including a flu clinic locator that can direct the public to get information on clinics in their area once information becomes available, visit www.immunizebc.ca.
For more information on the H1N1 flu virus, visit www.gov.bc.ca/h1n1.
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Robert Roos of CIDRAP took a long and fascinating look at the concept of Original Antigenic Sin a little over a month ago, albeit in a different context, in an article called 'Original antigenic sin': A threat to H1N1 vaccine effectiveness?.
He explains the concept far better than I could, and so I would refer you to his excellent article for more background.
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