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 At least 24 H7N9 flu infections and three deaths
have been confirmed in the past week by the World Health
Organisation (WHO), a dramatic increase on the two cases and one
death reported for the four-month summer period of June to
September.
"There's now a clear second wave of this virus," said Jake Dunning,
a researcher at Imperial College London who has been monitoring the
outbreak.
While the winter flu season means an increase in infections is not
unexpected, it also raises the risk of the virus mutating and
perhaps getting a chance to acquire genetic changes that may allow
it to spread easily from one person to another.
The H7N9 bird flu virus first emerged in March last year and has so
far infected at least 170 people in China, Taiwan and Hong Kong,
killing around 50 of them.
Many but not all of the people infected have had previous contact
with poultry or other birds, so for now, the fact that this virus
has apparently not adapted to easy human-to-human transmission is
one of the main features keeping a pandemic emergency response on
hold.
Yet the strain already has several worrisome features, including a
limited capability to spread from one person to another.
CLUSTERS
Several clusters of cases in people who had close contact with an
initially infected person have been reported in China. A scientific
analysis of probable H7N9 transmission from person to person,
published last August, gave the best proof yet that it can
sporadically jump between people.
A separate team of researchers in the United States said in December
that while it is not impossible that H7N9 could become easily
transmissible from person to person, it would need to undergo
multiple mutations to do that.
Another alarm was sounded, also last month, when scientists said
they had found that a mutation in the virus can render it resistant
to a key first-line treatment drug without limiting its ability to
spread in mammals.
WHO chief spokesman Gregory Hartl told Reuters the United Nations
health agency had noted the rapid increase in infections in the past
few weeks and is keeping a watchful eye.
"So far we haven't seen anything that cause us to change our risk
assessment," he said from WHO's Geneva headquarters
The WHO's current stance, based on its December 20 assessment, is
that five small family clusters have been reported but "evidence
does not currently support sustained human-to-human transmission of
this virus."
"The current likelihood of community-level spread... is considered
to be low," it says.
Flu viruses, however, often put on their biggest show of strength in
the cold winter months of January and February.
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And with more of the virus circulating in wild birds, poultry and
in the larger numbers of people infected in China and elsewhere, the
new strain now has more opportunity to adapt and mix with other
strains that may give it pandemic potential.
MIX AND MINGLE
Peter Openshaw, director of the Centre for Respiratory Infection at
Imperial College London, said the rising toll of infections and
deaths is "a signal for concern" because "historically what has
happened in major outbreaks is there are occasional, sporadic cases
and then it starts to build".
"But whether it means that there is any change in the virus'
behavior is another important question. If it were changing the way
it is behaving, that would be more alarming," he told Reuters.
Early gene analysis work on the emerging H7N9 virus in April last
year found it had already been circulating widely but went
undetected. During that activity, it had also acquired significant
genetic diversity, making it more of a threat.
Scientists warned then that its genetic diversity showed the H7N9
virus has an ability to mutate repeatedly and was likely to continue
doing so.
Dunning noted also that H7N9 is now more likely to meet and
potentially mix with other seasonal flu virus strains such as H1N1
and H3N2, which are circulating widely among people in China at the
moment.
"When you get hybrid viruses forming, that tends to occur in other
species, but there is always the potential for it to happen in
humans," he said. "So that is a theoretical concern."
Hartl agreed that the opportunity for the virus to take on more
features and capabilities is now greater, but stressed that such
changes may not necessarily present fresh dangers.
"Mutations happen all the time," he said. "And while yes, the more
virus there is, the more mutations could happen, it's also true that
almost all of these mutations are benign."
(Reporting by Kate Kelland; editing by
Tom Heneghan)
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