WHO: H1N1 could still mutate
2009-05-13 10:13
Geneva - The new H1N1 flu virus could
still mutate into a more virulent form and spark an influenza
pandemic that could be expected to circle the globe up to three
times, the World Health Organisation said on Tuesday.
The impact of any pandemic would vary, as a virus that
causes only mild illness in countries with strong health systems
can become "devastating" in those with weak health systems,
shortages of drugs and poorly equipped hospitals, it said.
The new virus, commonly referred to as swine flu, "appears
to be more contagious than seasonal influenza" and practically
the whole world lacks immunity to it, the WHO said in a document
entitled "Assessing the severity of an influenza pandemic."
Nikki Shindo of the WHO's global influenza programme said
that 10% of those infected with the strain in Mexico and
the United States needed to be admitted to hospital - far more
than the rate for seasonal flu, which kills up to 500 000 people
a year.
"This is clearly different than what we see from seasonal
influenza," Shindo told a news conference.
Despite this, she said most patients could recover from H1N1
with simple steps like hydration, and without any drug
treatment, raising questions about the rush to stockpile and
prescribe antivirals to treat the disease.
'Only for vulnerable patients'
The WHO will soon issue new guidance recommending that
Tamiflu and other antiviral drugs be used only for vulnerable
patients such as pregnant women and people with other health
problems such as diabetes and cardiovascular disease, she said.
"We will recommend to consider the use of antivirals for
high-risk groups or the group of people at increased risk,
depending on the availability," said Shindo, a medical officer
who heads WHO's clinical team.
Aspirin should not be used because of a risk of liver
damage, she added.
The Swiss drugmaker Roche said earlier on Tuesday it would
donate 5.65 million packs of its Tamiflu to the WHO to replenish
stockpiles deployed against the H1N1 outbreak and said it was
ramping up production of the drug.
European countries on alert for the flu, whose emergence
caused the WHO to declare a global pandemic is "imminent," have
been prescribing antivirals to treat those infected and reduce
the risk they will spread it to others around them.
'Less severe cases in Europe'
Shindo allowed that such aggressive therapy may have helped
reduce the severity of the disease outside its epicentre Mexico,
where 56 people have died from infection.
"It could be the
reason why we are seeing less severe cases in Europe," she said.
H1N1 flu has also killed three people in the United States
and one each in Canada and Costa Rica, according to WHO figures.
Few of the victims appear to have been completely healthy
before catching and succumbing to the flu, according to Shindo,
who said the new WHO guidance would reflect findings that the
strain was most dangerous to those with chronic health problems.
Governments will likely adopt a variety of strategies about
who should get antivirals, with the WHO guidance as a reference
point. "The countries have to make their prioritisation," Shindo
said. "There will be discussions about how to use it."
According to the United Nations agency's latest tally, some
5 251 people have been infected with H1N1 flu in 30 countries.
Severity of subsequent waves
The virus has caused mild flu-like symptoms such as nausea,
fever, and diarrhoea in most patients, and some people infected
with it have even been asymptomatic.
But flu strains mutate frequently and unpredictably and "the
emergence of an inherently more virulent virus during the course
of a pandemic can never be ruled out," the WHO said.
"The overall severity of a pandemic is further influenced by
the tendency of pandemics to encircle the globe in at least two,
sometimes three, waves," it said.
"For many reasons, the
severity of subsequent waves can differ dramatically in some or
even most countries."
The 1918 influenza pandemic - which killed tens of millions
of people - began mild and returned within six months in a much
more lethal form.
The 1968 pandemic began relatively mild, with
sporadic cases prior to the first wave, and remained mild in its
second wave in most, but not all countries.