Health

Seasonal Flu Shot Increases Risk of H1N1 Swine Flu?

by Scott Wu | September 24, 2009 at 10:51 am

3794 views | 43 Recommendations | 8 comments

Four Canadian studies found people who had received seasonal flu shots in the past were more likely to get H1N1 swine flu. The results are still preliminary, and has not been validated or peer reviewed.

"This is some evidence that has been floated. It hasn't been validated yet, it's very preliminary," said Dr. Don Low, microbiologist-in-chief at Mount Sinai Hospital in Toronto.

Theoretically, bacteria or virus can stimulate one's immune system to create antibodies, but at the same time facilitate the entry of another strain of virus.

This finding raises the debate between seasonal flu and swine flu, about whether or not they should delay, shorten, or cancel seasonal flu vaccination.

Across Canada, public health authorities are debating the idea of shortening, delaying or scrapping their seasonal flu vaccination campaign in favour of mass inoculation against H1N1.

The main reason is that H1N1 may be the dominant strain of influenza circulating when the fall flu season hits, meaning it could be a waste of time and resources to mount a seasonal flu vaccine campaign.

WHO said they are looking into the unpublished study. Marie-Paule Kieny said no researchers had presented similar findings, and it could be a "study bias".

"The reason why this may be different in Canada and in this particular study than in other places of the world is not yet identified. It may be a study bias, it may be that something is real," Kieny told a teleconference from the WHO headquarters.

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A. Tran

at 11:07 on September 24th, 2009

It would be a good idea for those scientists to follow up on this study and publish their reports for the public.

Thanks for post, SWU.

Scott Wu

at 11:11 on September 24th, 2009

I hope they will release more information soon. Everyone is so confused!

Yuliya Talmazan

at 12:09 on September 24th, 2009

Biologically speaking, this makes little sense. In principle, the common fall flu strain and the swine flu strain still have a lot of genetic similarity. Hence, the vaccine against the regular flu strain should stimulate the immune system to produce antibodies with protein locks that would disable the swine flu virus as well. Antibodies are proteins that bind the virus and do not let it replicate. If anything, the vaccine against the regular flu strain should render more protection against swine flu.

The only potential explanation I can find is that the swine flu, like the Spanish flu back in the day, tends to over-stimulate the immune system, resulting in the so-called "immune system storm" that causes the body to over-react to the virus, killing off body's own cells. So, instigating the production of yet more antibodies with regular flu vaccine can add to immune system over-stimulation and increase the risk of dying from swine flu. But, it will be very interesting to see what comes out of this.

Mary Richard

at 14:35 on September 24th, 2009

It looks like they're delaying the seasonal flu shot in Ontario, in all but the over 65 age group. I would tend to trust Mount Sinai, they've a good reputation. This has just come out:

Faced with puzzling but unconfirmed evidence that suggests a seasonal flu shot may raise the risk of catching swine flu, Ontario announced Thursday it is rescheduling its seasonal flu vaccine program to delay most of it until after pandemic vaccine has been administered.

At a news conference in Toronto, Dr. Arlene King, the province's chief medical officer of health, said the seasonal and pandemic vaccines will be delivered in three waves, starting in October.

People 65 and older, who have been largely spared by swine flu but who are at greater risk from seasonal flu, will be offered seasonal shots then. When the pandemic vaccine becomes available in November, all in Ontario who want to be vaccinated will be given access to those shots.

Once the pandemic vaccination effort is completed, Ontario plans to resume the seasonal flu shot program, which offers free vaccination to anyone who wants it. By then, said Dr. Vivek Goel, president of the Ontario Agency for Health Protection and Promotion, the questions about a possible link between seasonal shots and swine flu infection may have been answered.

Mary Richard

at 17:30 on September 24th, 2009

"Personally after this I am going to refuse my regular flu shot, as it seems it had no efficacy and was not important anyway, and pass on the H1N1 shot as it has been rushed into production by huge drug companies that have terrible reputations, with either zero or far too little testing, is being sold to me with a zeal that is just plain hysterical, and contains all kinds of nasty poisons."

I agree, Lorac. I've never gotten the flu shot for myself or my kids, I didn't feel it was necessary. Handwashing is, and it's always worked for us (knocking wood).

kath (not verified)

at 20:14 on September 24th, 2009

lorac, excellent suggestion - increasing vitamin D makes good sense!

Dr B (not verified)

at 09:56 on September 26th, 2009

The most likely explanation is that those who refused the seasonal vaccine last year are more at risk for complications of seasonal flu, and therefore equally at risk for H1N1. I think it was painfully irresponsible to release results of an unpublished, UNREVIEWED study during a period where everyone is so anxious about getting a vaccine.

Dr. B (not verified)

at 10:25 on September 26th, 2009

Forgive me, I had to respond to a code blue right as I was proofreading my message, and hit send too quickly- I meant that those who took (not refused) the seasonal vaccine last year are more at risk for complications of seasonal flu, and therefore H1N1. Interestingly, the "report" was that the younger subset showed this relationship, and not the older folks, which is because younger people who get seasonal flu shots generally have coexisting medical problems, hence increased risk of complicated H1N1.