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Speculations on the Origin and Future of H1N1

Friday, October 29, 2010 // Uncategorized

5/4/2009 10:24:08 PM

Flu viruses change slightly from year to year.  This is called antigenic drift. This is what the committee that determines what the components of next year’s vaccine deal with.  They try to predict the most prevalent strains next year.  Occasionally, viruses change a lot from the previous year.  This is called antigenic shift.  The following is an article from ProMed Digest that speculates on the origin of the H1N1 flu and what the future holds.

Biologists say there’s a good chance that the emerging flu strain
could establish itself as the dominant strain of influenza in future
flu seasons. Three times in the last century, a substantially new flu
virus has emerged and displaced the existing strains. That’s quite
different from the usual pattern in which the circulating virus
mutates just enough to keep vaccine makers tweaking their annual product.

“You can think of those strains, that vary from year to year, as
though they were cousins in the same family. They are variations on a
theme,” says William Schaffner at Vanderbilt’s medical school. But he
says the emergence of this new virus is different. This virus, which
originated partly in pigs, could be a game-changer. “This one is
completely new,” Schaffner says. “This one is a stranger in town.
We’ve never seen one like this before.”

The new swine flu virus has continued to spread, with more than 1000
confirmed cases and 20 deaths worldwide. All but one of the
fatalities occurred in Mexico, where officials decided Monday [4 May
2009] to allow most businesses to reopen on Wednesday. In the U.S.,
the number of confirmed cases stood at 253 in 36 states early Monday.

The new swine flu virus is not merely a case of the usual gradual
evolution. The big change scientists have seen with this strain is
called a “shift” [The term shift has usually been applied to a change
in antigenic type, e.g. from H1N1 to H2N2, etc., whereas the 2009
H1N1 is still H1N1-type. – Mod.CP]. The most infamous shift was the
virus that appeared in 1917 and caused the deadly flu pandemic of
1918. That virus then became the dominant variety of flu for several
decades. Then in 1957, it was displaced by another shift virus. There
was yet another shift in 1968, says Stephen Morse at Columbia
University’s Mailman School of Public Health. “There does seem to be
a rule of thumb about this, which is that every pandemic in the 20th
century essentially established the variants that would become the
circulating seasonal influenzas until the next pandemic came along to
displace them,” Morse says.

Each shift led to a stronger-than-usual flu season, but each one also
calmed down after a year or 2, once the population became exposed to
the new viruses or were vaccinated. Morse says the question now is
whether the new H1N1 swine virus will keep moving from
person-to-person efficiently. “If it continues like that, we’ll
expect to see this virus chugging along, and probably the next
seasonal influenza will be a descendent of this one,” Morse says.

The question, then, is how nasty the virus will end up being.
Professor John Oxford at St. Bart’s and the Royal London Hospital
says there’s some reason for cautious optimism. “In one sense, it’s
one of the mildest shifts, because most people on the planet have got
some memory, have come across H1N1 viruses since 1978,” Oxford says.

Even though health officials are calling this new virus H1N1, that’s
also the type of virus that’s in wide circulation today. And it has
an interesting history. It was the dominant flu virus through the
1920s, ’30s and ’40s. Oxford says it disappeared in 1957, when it was
displaced by another flu virus. But then a strain of H1N1 suddenly
reappeared in 1977. “Now where could it have come from?” he asks. “We
reckon now, in retrospect, it was probably released accidentally from
a laboratory, probably in northern China or just across the border in
Russia, because everyone was experimenting with those viruses at the
time in the lab.” It was nothing malicious, Oxford believes, just
some flu vaccine research that broke out of containment. The
descendents of this virus are still circulating. He notes that most
people who have encountered the newly emerged H1N1 virus seem to have
developed only mild disease, and he speculates that’s because we have
all been exposed to a distant cousin, the H1N1 virus that emerged in
the 1970s. “That escaped virus perhaps will provide some benefit now
in the face of this pig thing,” Oxford says.

This is well-informed speculation, not iron-clad assurance. And there
is another less reassuring lesson from the previous big shifts in flu
viruses. They caused mild disease when they 1st appeared in the
spring, but they all caused big flu seasons when they returned in the
fall as the new dominant virus. That’s one reason that health
officials are taking the new virus very seriously.

[Byline: Richard Harris]

[It is unwise to put much weight on speculation of this sort. There
have been few consistencies in the behavior of pandemic and
non-pandemic viruses. The descendants of 2 pandemic viruses, the H1N1
and H3N2 serotypes, were not displaced and continue to circulate
currently as seasonal influenza viruses. – Mod.CP]

– —
The challenge for vaccine makers and public health policy experts is what to do about the flu vaccine.  It is too late to add this virus to this year’s vaccine.  It would be necessary to come up with a completely new vaccine by this fall.  It’s unclear whether the resources exist to accomplish this.  The virus will probably circulate in the southern hemisphere, but may re-emerge in the fall.  Here’s another article which addresses this issue.

WHO will take vaccine gamble with swine flu
– ——————————————-
When World Health Organization [WHO] officials ask vaccine
manufacturers to start producing vaccine to fight swine flu in a few
weeks, they will be taking a calculated risk. Flu vaccine companies
can only make one vaccine at a time: either seasonal flu vaccine or
pandemic vaccine. Production takes months and it is impossible to
switch halfway through if health officials make a mistake. While some
countries like the United States may be better prepared than others
American officials say production for next year’s vaccine batch is so
advanced they’re nearly finished, whereas the situation for many
other countries is unknown.

About 70 percent of the world’s flu vaccines are made in Europe, and
the WHO is trying to figure out how many doses of seasonal flu
vaccine remain worldwide before asking vaccine manufacturers to start
pumping out pandemic vaccine instead. “It’s a big decision…We’ve
never done this before,” said Marie-Paule Kieny, director of the
WHO’s Initiative for Vaccine Research. Kieny said the decision would
be like guessing which vaccine the world will need most, but that the
WHO would try to hedge its bets by tallying existing seasonal flu
vaccine stocks. “We are gambling whether or not we will have enough
seasonal vaccine, but it will not be an ‘either-or’ situation,” she
said.

Vaccine makers can make limited amounts of both seasonal flu vaccine
and pandemic vaccine though not at the same time but they cannot make
massive quantities of both because that exceeds capacity. The
impending decision to make pandemic vaccine will also complicate
matters for countries in the southern hemisphere, where the flu
season is just starting. The WHO usually makes recommendations about
which seasonal flu strains should go into next year’s southern
hemisphere flu vaccine in September. But if vaccine manufacturers are
already making pandemic vaccine in the fall, that will mean fewer
doses of flu vaccine for people in the southern hemisphere.

Regular flu kills between 250 000 to 500 000 people worldwide every
year. So far, swine flu appears relatively mild, except in Mexico.
Until experts know how contagious and deadly the virus is, they won’t
know how many people actually need to be vaccinated. If it remains
mild, it is possible many people won’t need a shot. But if swine flu
evolves into a more deadly strain, more shots may be needed to
protect wider swathes of the population. Another possible
complication is that the pandemic vaccine will be made using the
strain available now; whether that will work if the virus mutates
isn’t certain. At the moment, the WHO has a bit of breathing space.
The key component for the pandemic vaccine, the “seed stock” from the
swine flu virus, will not be available for a few weeks. The WHO has
already put major vaccine makers on alert they may be asked to switch
to making pandemic vaccine soon. According to Chris Viehbacher, chief
executive of Sanofi-Aventis, Europe’s biggest vaccine maker, his
scientists are “working around the clock” on preparations for making
a swine flu vaccine for when the WHO comes calling.

But they too are waiting for more information. “It is premature to
forecast how many doses of swine flu vaccine we could produce,”
Viehbacher said, noting the company needs to see how much antigen,
the active ingredient in a vaccine, is required for each shot. If all
goes well, the 1st doses should be available several months after
production begins.

In the U.S., the government hasn’t yet decided what to order. “It
would all depend on how the outbreaks and the emergency unfolds,”
said Dr. Ruben Donis of the Centers for Disease Control and
Prevention, who is heading the U.S. vaccine work. Vaccine makers have
a few options when it comes to making pandemic vaccine. They could
add the pandemic strain to the regular vaccine, but adding that extra
strain reduces the number of shots you can make. Manufacturers might
also use adjuvants, components used to stretch a vaccine’s active
ingredient.

Recent work on H5N1 vaccines, the bird flu strain many thought would
ignite the next pandemic, may also help. John Treanor, a vaccines
expert at the University of Rochester said that adjuvants developed
during H5N1 research may come in handy now. He said public health
officials were indeed facing a vaccine dilemma. “There is only a
certain amount of capacity for vaccine manufacturing,” he said. “One
has to make some well-reasoned choices, sometimes based on incomplete
information.”

[Byline: Maria Cheng]

– —
Communicated by:
ProMED-mail Rapporteur Mary Marshall

[A question which has still to be addressed in this debate is the
extent to which vaccination with seasonal influenza virus vaccine
will provide some degree of immunity or amelioration of symptoms in
vaccinees. The symptoms of the illness in those experiencing
infection with the novel H5N1 strain with few infections have been
mild (the Mexican population apart). It would be interesting to know
to what extent this relates to the seasonal influenza virus history
of patients. – Mod.CP]

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