Avian influenza strain H7N9 was reported in humans in China in March 2013. Patients rapidly develop severe pneumonia that sometimes requires intensive care and mechanical ventilation. The mortality rate for the virus is over 30 percent, meaning that the need for a vaccine is urgent.
The University of Georgia’s vaccine has so far protected mice and guinea pigs against a lethal challenge of H7N9 and it is now viewed as a very strong candidate for human vaccine tests.
The researchers used parinfluenza virus 5, or PIV5, which is harmless in humans, but thought to contribute to upper respiratory infections in dogs, as a delivery vehicle for the H7N9 virus.
Small segments of H7N9 genes were placed inside PIV5, which was then used to immunize animals. While destroying the harmless PIV5 carrier, the immune system learnt to recognize and destroy H7N8 before it could cause severe illness.
“All of the vaccinated mice were protected against the N7N9 virus,” explained researcher Biao He. “But our experiments also revealed an unexpected result: The vaccinated animals did not produce a detectable level of antibodies. The antibody titer is the gold standard in vaccine development for influenza viruses, but our research brings that standard into question for H7N9 bird flu.”
The immune system has another way of fighting foreign invaders that does not involve antibodies - cell-mediated immunity. This process activates phagocytes, T-cells and other cells, all of which are able to destroy harmful viruses and bacteria.
“This suggests that our test subjects were protected through cell mediated immunity and the antibody titer may not be as reliable an indicator of immunity as we originally thought,” he said.
Investigations into the H7N9 vaccine will continue in additional animal models, and there is the hope that the discovery may lead to other researchers re-examining vaccines that did not produce a high antibody titer.