Vaccination was first used as a control measure for highly pathogenic avian influenza in Mexico in 1995. Use of vaccination with an inactivated oil-emulsion vaccine derived from H7N3 virus isolated from a duck was approved in 2012 as a control measure for the current H7N3 outbreak in response to the severe bird losses the industry was experiencing. This vaccine is still in widespread use and flocks are still becoming infected. There are veterinarians and poultry producers in Mexico who are asking the government to approve the use of an updated viral seed stock for making a new vaccine, which would have greater homology to the current field strain of the outbreak virus.
The basic idea behind updating the viral antigen used to make the virus is sound. Dr. Eduardo Lucio, director of IASA, a producer of avian influenza vaccine, explained, "It should be very similar to that used in the case of human influenza vaccines, where the laboratories that produce these vaccines must update their vaccine seeds every year.”
The problem is that even with better homology between the vaccine seed stock and the field strain of the virus, birds will still become infected when exposed to the field strain of the virus and will shed virus. Vaccination alone won’t eradicate the virus. Destruction of infected flocks and proper handling of manure from these flocks still need to be employed if the virus is to be eradicated. Relying on vaccination as the primary tool of control for avian influenza is a strategy for coping with the continued presence of the virus in the environment, not eradication.
Defining a successful avian flu vaccination program
Many in Mexico consider the avian influenza vaccination program to be a success, because it has reduced the losses and prevented the Mexican poultry industry from being wiped out. Just as the avian influenza virus rapidly spreading across the state of Jalisco caused Mexican poultry producers to ask for approval to vaccinate, the quick movement of the H5N2 virus through turkey and egg laying operations in the Upper Midwestern U.S. have brought similar calls for approved use of vaccination.
In the U.S., there is hope, that if vaccination is approved for use to control the current H5N2 outbreak, that success will be defined differently. When asked to comment on the experience with avian influenza vaccination in Mexico, Dr. John Glisson, vice president of research programs, U.S. Poultry & Egg Association, said that in spite of vaccination programs, avian influenza virus has been endemic in Mexico for 20 years. “We consider eradication as the measure of success,” he said.
The avian influenza outbreaks in the U.S. and Mexico have shown that the poultry industry’s biosecurity programs in both countries have failed to halt the spread of highly contagious viruses. Practices in both countries will need to change, in some cases very fundamentally, if the negative impact of future outbreaks is to be minimized. Vaccination is only a long-term option if you have given up on eradication.