Unpublished Canadian data are raising concerns about whether it's a good idea to
get a seasonal flu shot this fall and fuelling a drive by some public health
officials in Canada to delay, reduce or scrap altogether campaigns to vaccinate
against seasonal flu this year.
Drawn from a series of studies from
British Columbia, Quebec and Ontario, the data appear to suggest that people who
got a seasonal flu shot last year are about twice as likely to catch swine flu
as people who didn't.
A scientific paper has been submitted
to a journal and the lead authors - Dr. Danuta Skowronski of the British
Columbia Centre for Disease Control and Dr. Gaston De Serres of Laval University
- are consequently constrained about what they can say about the work. Journals
bar would-be authors from discussing their results before they are published.
Skowronski, who initially declined to
speak after news of the findings leaked to the media, said it's important that
the work gets the expert scrutiny the journal peer-review system provides.
"Good scientists know that methods
can influence results," she said Wednesday night from Vancouver.
"For me, it's very important that we
respect the peer-review process as good scientists. Because the implications ...
are important. And if there are methodologic flaws, we need to be assured that
every stone was turned over to make sure what we're reporting is valid."
"Epidemiologists are taught there a
limited number of explanations for results," she continued. "Either they're
real, they're due to chance or they're due to bias or to confounding. And so
it's going to have to be in one of those categories and that's true of any study
conducted anywhere."
While few people appear to have
actually seen or read the study, the puzzling findings have been a poorly kept
secret and many in the public health community in Canada have heard about them.
The findings are causing
consternation abroad as well, with officials at public health agencies and even
at the World Health Organization worried the alleged link will deter people from
getting vaccinated in a fall when many are being urged to get both seasonal and
pandemic flu shots.
The Public Health Agency of Canada
was informed of the findings some time ago and has been seeking help here and
internationally to try to figure out if the effect is real or if the studies are
flawed.
"An arms-length review of the various
methods is currently underway to assess the validity of the studies relative to
that observation," Dr. David Butler-Jones, Canada's chief public health officer,
said via email.
"We are also examining other data
that will help to understand what if any association there is. We look forward
to the results of the review and other data to inform our recommendations as we
go forward."
The U.S. Centers for Disease Control
also knows of the work. It said it has looked for similar evidence in the United
States but sees none.
"It is difficult to speak about a
study that has yet to be published, however, as this is an important issue
involving the subject of seasonal influenza and the fast moving global pandemic
of 2009 H1N1 influenza it is important to note the scientists at the Centers for
Disease Control and Prevention have not seen this effect in systems we have
reviewed in the United States," spokesperson Joe Quimby said by email.
A number of influenza and infectious
diseases experts know of but are unwilling to speak publicly about the paper.
But several were quick to note that British and Australian researchers haven't
seen the phenomenon either. The lack of corroboration in other jurisdictions is
"a red flag," said one expert, who believes the findings will be shown to be due
to a study flaws.
Another flu expert who was willing to
speak on the record said they do not make sense to him either.
"I cannot think of a good reason why
this is biologically likely, especially since we have sufficient evidence now
that ... there is priming in the population by the way the vaccine is working,"
said Dr. Arnold Monto, of the University of Michigan.
He was referring to the fact that
studies of swine flu vaccine show a single dose induces a strong and likely
protective response in teens and adults. That suggests humankind's long exposure
to seasonal H1N1 viruses has "primed" or awakened our immune systems to
recognize the new virus and fight it off.
Dr. Donald Low, chief microbiologist
at Toronto's Mount Sinai Hospital, was reserving judgment on the findings. But
he said this kind of effect of previous exposure raising the risk of future
illness is seen in some diseases, like dengue fever.
"We don't see that in flu," Monto
countered.
Low said it is important to get to
the bottom of the issue, but in the meantime, delaying the use of seasonal flu
vaccine makes sense for logistical reasons. Swine flu activity is on the upswing
in the U.S. and in parts of British Columbia, and focusing on speeding delivery
of that vaccine makes more sense now, he said.
"If we're going to try to protect
people, this is the virus we should be trying to protect them against," Low
said, suggesting decisions on whether to try to vaccinate against seasonal flu
can be done later in the season.
He admitted the controversy could
undermine the public's willingness to be vaccinated against influenza.
"This is obviously difficult for
public to be able to digest this," he said. "There's a crying need here for a
prospective randomized controlled study."
That type of study - which is not the
kind on which the findings are based - is considered the gold standard of
medical evidence. They are also costly and Skowronski said it wouldn't be
feasible to mount one in time to help public health officials faced with the
current dilemma of whether to push seasonal flu vaccine this year or not.
"If it was possible, we would have
attempted it," she said.