Most people probably have little innate immunity against the new bird flu virus in China, according to alarming new findings.
British researchers conducted a study in the nearby country of Vietnam and found the level of immunity was "very low."
So far 36 deaths from the H7N9 virus have been reported in south-east China from an outbreak thought to centre on pigeon and poultry markets in Shanghai. Another 95 cases of infection have been identified.
The researchers from the Wellcome Trust Oxford University Clinical Research Unit, based in Vietnam, tested people in rural and urban Vietnam.
They say that Vietnam would be especially vulnerable if the flu outbreak were to jump the Chinese borders.
The findings, which used new techniques developed in the Netherlands, show that the new virus is not widely found in south-east Asia. they have been reported in the Journal of Infectious Diseases.
Researcher Dr Maciej Boni said: "H7N9 is a virus that until now has only infected birds so it’s not surprising that we don’t find much evidence of humans having been exposed to it.
"It is reassuring that in Vietnam we don’t see any evidence that the current outbreaks represent a tip-of-the iceberg observation of widespread H7N9 infection in people.
"On the other hand, the low antibody levels indicate that there is likely to be very little immunity to this virus."
Dr Boni added: "It has been suggested that people who live in closer proximity to chickens and other birds will have higher levels of immunity to bird flu viruses simply because their exposure is likely to be greater. However we find no evidence for this."
Centre director Professor Jeremy Farrar said the findings should be treated with caution – as it was not clear how much immunity the new technique measured. The technique measures levels of antibodies.
He said: "These new techniques do allow for much higher throughput of samples, ease of use and once validated may allow much more rapid assessment of the spread of infection and levels of population immunity than do traditional assays."
M. Boni et al. Population level antibody estimates to novel influenza A/H7N9. Journal of Infectious Diseases 17 May 2013 [abstract]
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