Population Immunity to H7N9 Could Be Low

H7N9 bird flu immunity study shows low immunity to the virus in Vietnam

(RxWiki News) Cases of H7N9 avian influenza in China have had experts worldwide on edge since the end of March. There is still much to be learned about the new bird flu strain, inspiring researchers in Vietnam to probe deeper.

A new study aimed to investigate human immunity to H7N9 in the general population and found that immunity seems to be low and comparable to human immunity to other avian flu strains.

"Cover your mouth when coughing."

Led by Maciej F. Boni, PhD, of the University of Oxford in the United Kingdom and the Wellcome Trust Major Overseas Programme in Vietnam, researchers gathered 1,723 blood serum samples in southern Vietnam.

Samples were obtained at hospitals in Ho Chi Min City and Nha Trang between 2010 and 2012.

The samples were tested for antibodies for five different bird flu antigens, including those of subtype H5. A virus of this subtype, the H5N1 avian flu, caused hundreds of deaths during an Asian outbreak in the early 2000s.

The researchers found that titers (concentrations) of antibodies that fight viruses in the subtype H7 were higher than levels of antibodies to fight subtype H5, but lower than antibody levels to fight subtype H9.

The authors reported that geometric mean titers (average concentration scores) were 23.1 for H9, 19.0 for H7, 13.5 for subtypes H5/10 and H5/07 and 11.1 for H5/04.

“This indicates that immunity to subtype H7 viruses should be low and comparable to that of other avian influenza viruses,” explained the authors.

The researchers also found that antibody titers to all bird flu antigens increased with age, which was not a surprise.

“Diversity of influenza antibodies increases with age, as individuals accumulate an antibody repertoire to their different influenza infections, and it becomes more likely that these antibody populations are able to bind antigens from certain avian influenza viruses,” wrote the authors.

The authors did not find differences in antibody titers among samples from the two different hospitals (one of which served more rural patients) or among those who owned domestic poultry and those who did not.

The authors did note that it cannot yet be confirmed that differences in these antibody titers equal differences in clinical protection against the viruses. More research is needed to explore the topic.

There have been 131 cases of H7N9 discovered in China, 36 of which have caused fatalities. No new cases have been reported since May 8.

The study was published online on May 17 by the Journal of Infectious Diseases. No conflicts of interest were reported. 

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Review Date: 
May 21, 2013