When flu viruses 'shift and drift', how many vaccines?

Aug 29, 2009 by Marlowe Hood

The World Health Organisation's announcement Friday that the 2009 H1N1 virus has become the dominant strain of flu worldwide fits a historical pattern, but the impact on vaccine policy remains unclear, a top expert said.

"This was one of the big questions, whether we would finish up with three types of strains, or whether one would replace the others," said Nigel Dimmock, a virologist and emeritus professor at the University of Warwick.

Dimmock said it was surprising that the WHO had decided so rapidly that the pandemic strain -- which surfaced in Mexico four months ago -- had elbowed out other flu strains.

The northern hemisphere has not yet begun, so the determination must have been based mainly on what has happened in southern hemisphere countries such as Australia, New Zealand, Argentina and Brazil, he said.

The WHO said in a communique: "Evidence from multiple outbreak sites demonstrates that the H1N1 pandemic virus has rapidly established itself and is now the dominant in most parts of the world."

Human flu viruses are identified by a surface-lying protein called hemagglutinin -- the "H" of A(H1N1).

There are 16 subtypes of the "H" protein that circulate in birds and swine, but so far only three have become easily transmissible among humans.

"Flu viruses go through 'shift and drift', explained Mark Miller, an epidemiologist at the US National Institutes of Health's Fogarty International Center.

"In previous we had a shift in the type of virus that is dominant," and then a process of 'drift' and it changed slightly from year-to-year.

The deadly 1918 "Spanish flu" -- which left some 40 million dead -- was an H1 virus, and dominated unchallenged until 1956 when a new "H2" variant swept across the globe.

"It pretty much at a stroke replaced the H1N1. It is still amazing how that happened -- nobody really knows why," Dimmock said.

The same thing happened a dozen years later, when the "H3" knocked its predecessor off the world stage. This led scientists to conclude that any new pandemic strain replaces the seasonal one descendent from the previous pandemic.

"But then the H1N1 reappeared in 1977, very similar to the strains circulating in the mid-1950s, and it has been co-circulating with the H3N2 up until the start of this year," Dimmock said.

It was unclear based on the WHO's statement, he added, whether people would need to vaccinate against only the new virus, or against the two strains that have been around for decades as well.

"If the pandemic has replaced the other strains, as happened in 1957 and 1968, then you don't need the old ," Dimmock said by phone.

"But if they continue to co-circulate, even if it is dominant, then you are going to need a vaccine with three type-A components -- and a seasonal B."

The vaccines can be combined into a single shot, or given separately he said.

(c) 2009 AFP

Explore further: Mali announces new Ebola case

add to favorites email to friend print save as pdf

Related Stories

Study uncovers cause of flu epidemics

Mar 04, 2008

The exchange of genetic material between two closely related strains of the influenza A virus may have caused the 1947 and 1951 human flu epidemics, according to biologists. The findings could help explain why some strains ...

Officials say swine flu vaccine may not be ready by fall

Jun 12, 2009

As the World Health Organization declared a global flu pandemic Thursday, raising the alert to its highest level, federal health officials said it was unclear whether an effective vaccine would be available by fall.

Researchers describe the 90-year evolution of swine flu

Jun 30, 2009

The current H1N1 swine flu strain has genetic roots in an illness that sickened pigs at the 1918 Cedar Rapids Swine Show in Iowa, report infectious disease experts at the University of Pittsburgh Graduate School of Public ...

Recommended for you

Can robots help stop the Ebola outbreak?

45 minutes ago

The US military has enlisted a new germ-killing weapon in the fight against Ebola—a four-wheeled robot that can disinfect a room in minutes with pulses of ultraviolet light.

New bird flu case in Germany

46 minutes ago

A worrying new strain of bird flu has been observed for the first time in a wild bird in northern Germany, the agriculture ministry said Saturday.

Mali announces new Ebola case

Nov 22, 2014

Mali announced Saturday a new case of Ebola in a man who is fighting for his life in an intensive care unit in the capital Bamako.

Plague outbreak kills 40 in Madagascar: WHO

Nov 22, 2014

An outbreak of plague has killed 40 people in Madagascar, the World Health Organization said, warning that the disease could spread rapidly in the country's densely populated capital Antananarivo.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.