One in five infected by pandemic flu
2013-01-26 10:04
Paris - More than a fifth of the world's population was
infected by the H1N1 virus in the 2009-2010 flu pandemic, according to new
estimates released on Friday.
The study confirms warnings that so-called swine flu was
highly contagious.
It also estimates that the flu's lethality - as
previously reported - was low.
Between 20 and 27% of people were infected by the virus,
the investigators reported in a specialist journal, Influenza and Other
Respiratory Viruses.
Children aged 5 to 19 had the highest rates of infection,
accounting for 47% of the total. Older people aged 65 and above accounted for
11%.
The probe aims to give the most complete picture of the
pandemic to help future preparations for flu outbreaks.
The 16-month episode sparked a surge in demand for
vaccines, prompting critics to accuse health watchdogs of scare-mongering.
By the time the pandemic was officially over in August
2010, countries had notified the UN's World Health Organisation (WHO) of less
than a million infections and around 18 500 deaths, but this has always been
known to be a small fraction of the toll.
The new study is based on data from 27 pieces of research
that looked for traces of antibodies to H1N1 in more than 90 000 blood samples
collected in 19 countries.
Presence of the antibodies is a telltale of infection,
but does not in itself mean the individual fell ill.
The investigation was not designed to look at mortality
rates, but the authors say the data it provided, when compiled with other
estimates, suggest 0.02% of cases - one in 5 000 - ended in death.
That figure is in the low range of death tolls from
annual "seasonal" flu.
By comparison, the 1918-1919 pandemic of
"Spanish" flu, which killed tens of millions of people, is estimated
by some to have had a case fatality ratio of 2.5 to 3%.
The study was led by the WHO and Imperial College London.
Data came from, among others, Britain, China, France,
Germany, Hong Kong, India, Iran, the US and Vietnam.
The results from these countries were then extrapolated
for a planetary-wide figure.
