# 7302
An open access study recently published in the Journal of Infectious Disease analyzes serum samples gathered from 1723 individuals from Southern Vietnam between 2010-2012.
Researchers checked them for IgG antibodies to the HA1 region of 5 avian flu viruses and 11 human flu viruses.
While not testing directly against the H7N9 virus - (they used the 2003 H7N7 virus from the Netherlands which has an HA that is a 96% match for the HA of the emerging H7N9) - this antigen would reasonably be expected to produce a significant serological cross reaction to H7N9 antibodies.
It’s a fascinating study and you’ll probably want to read it in its entirety. I’ve a link to the study, excerpts from abstract, then close with some excepts from the press release.
Population-level antibody estimates to novel influenza A/H7N9
Maciej F Boni, Nguyen Van Vinh Chau, Nguyen Dong, Stacy Todd, Nguyen Thi Duy Nhat, Erwin de Bruin, Janko van Beek, Nguyen Tran Hien, Cameron P Simmons, Jeremy Farrar, Marion Koopmans
Abstract
There are no contemporary data available describing human immunity to novel influenza A/H7N9. Using 1723 prospectively collected serum samples in southern Vietnam, we tested for antibodies to five avian influenza antigens using a protein microarray.
General-population antibody titers against subtype H7 virus are higher than antibody titers against subtype H5, and lower than titers against H9. The highest titers were observed for human influenza subtypes. Titers to avian influenza antigens increased with age and with geometric mean antibody titer to human influenza antigens. There were no titer differences between the urban and the rural location in our study.
This study checked for antibodies to 3 different H5 viruses, the H7 virus noted above, and the H9N2 virus – which is not only ubiquitous in poultry across much of Asia, but has also contributed the internal genes to both H5N1 and the H7N9 virus.
The entire study is available, and it includes a good deal of discussion of the methods, limitations to this type of antibody analysis, and results obtained.
The authors found that antibody titers increased with age for all avian flu antigens, as they did with human flu strains.
Their assumption is that exposure to avian strains is likely low, and these results are more likely due to the cross-reactivity of antibodies from past infections with human flu strains.
Jumping to the end, the authors write.
Population-level immunity appears to be low to influenza A/H7N9 and comparable to what we observe for other avian influenza viruses. In southern Vietnam, we do not see evidence that the current H7N9 outbreaks represent a tip-of-the-iceberg observation of widespread H7N9 infection.
We observed no differences between two areas with low and high levels of domestic poultry ownership, indicating that poultry ownership does not have an effect on avian influenza exposure or avian influenza antibody levels. If the H7N9 outbreaks develop into a human transmissible epidemic, the current results will serve as a baseline for interpreting population level serology after the first wave of infections.
For more on this Welcome Trust has a press release which provides more background and context for this study.
Estimates reveal low population immunity to new bird flu virus H7N9 in humans
The level of immunity to the recently circulating H7N9 influenza virus in an urban and rural population in Vietnam is very low, according to the first population level study to examine human immunity to the virus, which was previously only found in birds. The findings have implications for planning the public health response to this pandemic threat.
The study used a new, high throughput method that allows blood samples to be analysed for antibodies to multiple human and animal influenza viruses at the same time and is easier to standardise than previous techniques. However, the assay is yet to be validated clinically for the H7N9 virus, and the researchers caution that the results must be interpreted with care.
<SNIP>
The results reveal that although the level of antibodies to the H7 sub-type of flu virus are higher than any of the H5 sub-types tested, levels of antibodies to all five bird flu viruses are much lower than to human flu viruses. This suggests that people living in this particular area of Vietnam have had very little or no exposure to the H7 sub-type of virus, similar to other bird flu viruses. As this population of people would be expected to be among the first to be affected in the event of a pandemic, these findings have important implications for pandemic preparedness plans in this area.
<SNIP>
Professor Marion Koopmans, who is Head of Virology at the RIVM and senior author of the study, said: "We developed this technique exactly to be used in the current situation: we wanted a standardised test that allowed us to rapidly compare antibodies to the new virus with those to influenza viruses that we already know are common in people. The level of immunity to a new virus is one of the important questions during any emerging disease outbreak. We need only one drop of blood, so that tests can also be run when only small sample volumes are available, for instance when testing children. For outbreak investigations, testing of animals may be needed, and we are currently working on that. To do the clinical validation studies, we need blood samples from patients (and animals) with confirmed H7N9, and we hope to be able to do that soon through collaborations with other groups working on H7N9."
