VN's Bird Flu Control Measures Largely Successful

VIET NAM - There were marked differences in the within-flock transmissibility of highly pathogenic avian influenza (HPAI) H5N1 before and after the introduction of a control policy that included vaccination, say researchers who have evaluated the control of the infection in Viet Nam.

9 June 2010

3 minute read

Dr R. Soares Magalhaes of the UK's Royal Veterinary College and colleagues there and at FAO in Rome have studied the control of highly pathogenic avian influenza (HPAI) H5N1 in Vietnam in terms of virus transmission within infected flocks reported before and after vaccination. Their paper is published in BMC Veterinary Research.

In the introduction to their paper, the researchers explain that currently, the HPAI virus of the sub-type H5N1 is believed to have reached an endemic cycle in Viet Nam. They used routine surveillance data on H5N1 poultry outbreaks in that country to estimate and compare the within-flock reproductive number of infection (R0) for periods before (second epidemic wave, 2004-5; depopulation-based disease control) and during (fourth epidemic wave, beginning 2007; vaccination-based disease control) vaccination.

Results

The researchers say that their results show that infected premises (IPs) in the initial (exponential) phases of outbreak periods have the highest R0 estimates. The IPs reported during the outbreak period when depopulation-based disease control was implemented had higher R0 estimates than IPs reported during the outbreak period when vaccination-based disease control was used.

In the latter period, in some flocks of a defined size and species composition, within-flock transmission estimates were not significantly below the threshold for transmission (R0<1).

Conclusions

Magalhaes and co-authors conclude that the current control policy based on depopulation plus vaccination has protected the majority of poultry flocks against infection. However, in some flocks the determinants associated with suboptimal protection need to be further investigated as these may explain the current pattern of infection in animal and human populations.

Reference

Magalhaes R.J.S., D.U. Pfeiffer and J.Otte. 2010. Evaluating the control of HPAIV H5N1 in Vietnam: virus transmission within infected flocks reported before and after vaccination. BMC Veterinary Research 6:31. doi:10.1186/1746-6148-6-31.