Previous research conducted by the University of
Cambridge showed that H3N2 viruses circulate continuously in East and
Southeast Asia throughout the year, spreading to the rest of the world
to cause seasonal flu epidemics. Given the fundamental similarities
between H3N2, H1N1 and B viruses it was thought that H1N1 and B viruses
would also emerge from East and Southeast Asia to cause yearly epidemics
worldwide.
However, the work published today in Nature
shows that while H3N2 viruses die out between epidemics and new viruses
emerge from East and Southeast Asia every year, H1N1 and B viruses
frequently circulate continuously between epidemics worldwide, which
gives rise to a huge diversity in these viruses.
Doctor Ian Barr, Acting Director WHO Collaborating
Centre for Reference and Research on Influenza (WHO CC) and co-author
said, “This work represents another piece in the complex puzzle of
influenza virus circulation and human infections and provides insights
that will help develop better influenza vaccines that match strains
circulating in the community.
“In summary, while the spread of influenza in Asia is a
good indication of which H3N2 virus might spread worldwide, it’s only
part of the solution.”
The key element to global movement is who is getting
infected: faster evolving viruses, like H3N2, can infect adults who tend
to travel more frequently than children, providing more opportunities
for the virus to spread. Conversely, more slowly evolving viruses, such
as H1N1 and B viruses, primarily infect children. Children get sick with
all four seasonal flu viruses, but H3N2 evolves faster so it infects
adults more often. This leads to a greater proportion of adult
infections with H3N2 relative to H1N1 and B viruses, and faster spread
of H3N2 viruses.
The Nature study also sheds important light on
the role of India in the global spread of seasonal influenza viruses.
Scientists and public health officials had long known that China and
Southeast Asia were important for the evolution and spread of seasonal
influenza viruses. However, based on the analysis of an extensive
collection of viruses from India, it is now clear that India may be as
central as China to the ongoing evolution of seasonal influenza viruses.
Director of the Doherty Institute, Professor Sharon
Lewin, congratulated Dr Barr, Associate Professor Aeron Hunt, Acting
Deputy Director WHO CC, and Professor Anne Kelso, Honorary, DMI, on
their involvement in this exciting research and said the work was a
great credit to the Doherty Institute’s multi-disciplinary program to
develop effective new ways to prevent and treat influenza.
“The ultimate goal is to create a one-shot flu vaccine
that will provide immunity against all strains, replacing the need for a
yearly vaccination. The research outlined in Nature provides us with more evidence and information to help us achieve this goal.
“The WHO CC at the Doherty Institute is one of only five
such Centres in the world and plays a vital role in analysing influenza
viruses in circulation across the globe, which is then used by the WHO
to determine the strains to be included in the annual seasonal
vaccination.”
The research was primarily funded by the Royal Society
and US National Institutes of Health with extensive involvement of the
WHO’s Global Influenza Surveillance and Response System.