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H1N1 Vaccine Safety/ Seasonal Vaccine and H1N1

Friday, October 29, 2010 // Uncategorized

10/7/2009 6:03:36 PM

I’ve been at the annual meeting of the Texas Club of Internists in Toronto.  This has involved three days of meetings and has left little time for blogging.

Here are a couple of interesting news items on H1N1.

H1N1 Update: CDC Offers Reassurance on Vaccine Safety and Availability
The CDC addressed fears over 2009 H1N1 vaccine safety and availability at a press briefing Tuesday.
CDC Director Thomas Frieden addressed “three major concerns that people have” — that 2009 H1N1 is “just a mild illness”; that the vaccine may not be safe; and that it’s already too late to be vaccinated.
Dr. Frieden countered with a reminder that 2009 H1N1 has killed many people and will likely kill more. Regarding safety, he said that the vaccine is made in the same way and in the same facilities as seasonal vaccines, which have an excellent safety record. And as to the futility of vaccination, he said, we “don’t know what the rest of this long flu season is going to hold. We haven’t had a flu season like this in at least 50 years.”
He added: “We’re very confident that there will be plenty of vaccine for everyone who wants to be vaccinated. It won’t be available when everyone wants to be vaccinated.”

This is also encouraging:

H1N1 Update: Seasonal Flu Vaccine Seems to Offer Some Protection Against 2009 H1N1

Vaccination against seasonal strains of flu seems to offer some protection against 2009 H1N1 virus, particularly severe infections, according to a retrospective study published online in BMJ.
Researchers examined vaccination status in 60 laboratory-confirmed cases of 2009 H1N1 compared with that in 180 matched controls. All subjects were patients in a respiratory disease hospital in Mexico City during the early months of the pandemic. Cases had been admitted for influenza, and controls were treated for diseases other than influenza or pneumonia.
Cases were less likely than controls to have received the seasonal vaccine (13% vs. 29%). Among the cases, those who’d been vaccinated were less likely to die.
The authors urge caution in interpreting the results, which they say “in no way indicate that seasonal vaccine should replace vaccination against pandemic influenza.”

This report is at odds against a report from Canada that suggested that previous seasonal flu vaccine increased the risk of catching H1N1.  If you want to read more about the dicussion on that read further from Promed Digest:

No need to change vaccine policy based on Canadian flu data: WHO
– —————————————————————-
International influenza vaccine experts are apparently not convinced
that Canadian researchers have found a true link between getting a
seasonal flu shot and catching swine flu [see: ProMED-mail posting
“Influenza pandemic (H1N1) 2009 (59): Canada, vaccination
20090929.3400”]. The consensus that emerged from a World Health
Organization (WHO) teleconference Friday [2 Oct 2009] on the
controversial data seemed to be that the Canadian findings are likely
due to some confounding factor or factors in the data themselves and
may not reflect a real increased risk, according to a WHO official who
helped pull together the meeting.

“From a WHO point of view, the fact that the findings are not
replicated in other countries I think is reassuring for us that this
is an outlier, if you like, the unexpected findings that are coming
out of Canada,” said David Wood, coordinator of the quality, safety,
and standards team of WHO’s department of immunization, vaccines, and
biologicals. “Most people are still looking at this as some sort of
undetected confounding in the data, that for some reason is giving the
results that are there.”

In an interview from Geneva, Wood was diplomatic. But when pressed, he
did admit most experts on the call didn’t seem to believe that the
unpublished study, based on data from British Columbia, Quebec, and
Ontario, had found a true link between getting a seasonal flu vaccine
and having an increased risk of coming down with a mild case of H1N1
flu. “Well, yeah,” he said. “It’s a totally unexpected finding.” “So I
think people do then try to think: ‘Well, why is this happening? Are
there some effects that are just not being detected that are really
behind this?’ Because it is an unexpected finding. That’s the way
people tend to think.”

The work, which is [reportedly] being considered for publication by a
medical journal, contributed to decisions by most provinces and
territories to stagger or delay their seasonal flu shot efforts this
fall [2009]. Instead of launching full-fledged seasonal flu vaccine
programs in October [2009], most have announced they will offer
seasonal shots in October only to seniors — who aren’t currently at
high risk from the pandemic H1N1 virus — and residents of long-term
care facilities. After pandemic vaccination efforts are completed,
most of those provinces plan to offer seasonal vaccine more broadly.

A couple of jurisdictions — Quebec and Nunavut — will wait until
after they’ve completed their pandemic vaccination efforts before
offering seasonal flu shots. At the other end of the spectrum, New
Brunswick is going ahead with its regular seasonal flu shot campaign
before offering pandemic flu shots.

The Canadian findings, which are reportedly mirrored in data from
Manitoba as well, suggest that people who got a flu shot last fall
[2008] were twice as likely as people who didn’t to contract swine
flu. But the association, if it is real, is to mild disease. There is
no evidence that people who got seasonal flu shots are more prone to
develop severe illness if they catch the new H1N1 virus.

Scientists from the United States, Britain, and Australia have looked
at their data but didn’t see the same effect. A number of scientists
have speculated that the Canadian data may have some built-in
confounders — factors that can produce false results. For instance,
if people who get flu shots are also more likely to seek a diagnosis
of swine flu if they get sick, that could make it seem like more of
them got the illness when in fact what happened is that more of their
illnesses were recorded.

But if the Canadian results are due to some statistical flaws or
selection biases, no one on the 4 1/2-hour teleconference was able to
put a finger on what exactly the problem is, Wood acknowledged. And he
admitted there may not be a satisfactory answer to that puzzle in the
foreseeable future. “It didn’t seem very likely that we’re going to be
able to ….. suddenly come up with the magic explanation as to why
the Canadian data are different to others,” Wood said. “In the short
term, this is really probably as far as we’re going to get.”

New studies will likely be needed to get a definitive answer, he said.
Experts say there will need to be prospective studies — following
people who get a flu shot forward — rather than the retrospective
studies that produced the unusual findings. The evidence from
retrospective studies isn’t considered as high quality as that
garnered from prospective studies.

In the meantime, a summary of the situation will be presented to the
WHO’s Strategic Advisory Group of Experts on immunization, also known
as SAGE. The group, which meets later this month [October 2009], makes
recommendations for the WHO on vaccination policy. Wood said he
couldn’t prejudge what the committee will decide, but said for the
moment it doesn’t seem like the WHO needs to ask countries to change
their vaccination programs for this fall [2009]. “The fact that it’s
just been seen in Canada at the moment, I don’t think that that’s
going to force global policy changes,” he said.

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