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We see from the passage that although the H5N1 strain of the avian flu virus is not easily transmitted from person to person at present, ----.
Virologist Robert Webster thinks that the H5N1 strain
of the avian influenza virus poses the most serious
public health threat since the Spanish flu pandemic
of 1918, which killed an estimated 40 million to 100
million people worldwide. Although the H5N1 strain
has so far shown no signs that it has acquired the
ability to transmit easily from person to person,
Webster says that it is only a matter of time before it
does. For that to happen, Webster and others believe
that a version of the human flu virus, which is easily
transmittable between people, and the H5N1 avian
virus would have to infect the same mammalian cell
at the same time and re-combine their DNA. If H5N1
picks up those genes from the human flu virus that
enable it to spread from person to person, Webster
says that virtually nobody will have immunity to it,
and many deaths may ensue.