Researchers develop universal influenza vaccine for animals

Dec 14 2008

A University of Maryland-led science team has developed a universal influenza vaccine for animals that may help prevent or delay another human flu pandemic.

Led by Daniel Perez, a University of Maryland associate professor and virologist, the team has developed a vaccine component that can be used to immunize both birds and mammals from dangerous forms of the flu, including the highly lethal H5N1 avian influenza strain.

This new universal influenza component promises to make it much easier to create a human vaccine capable of protecting humans against lethal avian bird flu strains. In addition, it can be used to vaccinate wild and domestic birds or other species, thus reducing the spread of flu viruses among these populations and decreasing the chance that deadly new human flu strains will spring from these animal reservoirs.

"We now have a vaccine that works in many animal species and can protect against any type of influenza that we want," Perez said, who does his research at the College Park campus of the Virginia Maryland Regional College of Veterinary Medicine (Avian Flu Virus Program).

From Vaccine to Virus

The vaccine for a virus is derived from the virus. The vaccine mimics the presence of the virus without causing disease, priming the body's immune system to recognize and fight against the virus. The immune system produces antibodies against the vaccine that remain in the system until they are needed. If that virus, or in some case a closely similar one is later introduced into the system, those antibodies attach to viral particles and remove them before they have time to replicate, preventing or lessening symptoms of the virus.

Perez and his team used genes from the avian flu virus H9N2 to create a live, weakened flu vaccine. This type of vaccine consists of a living but weakened form of a virus that is generally harmless.

"H9N2 is another avian influenza virus with a broad host range. It can infect both birds and mammals," Perez said. "We wanted to try to use the backbone of that virus to create a live but weakened form of the virus and make a one-size-fits-all universal vaccine."

They isolated genes from the H9N2 virus to make up a "backbone" that consists of internal genes common to other flu strains. The backbone can be used as a starting point from which to quickly create other live, weakened flu vaccines because it can be genetically modified at the surface to resemble particular flu viruses for the purposes of vaccination.

"We can attach any surface proteins to this backbone to make a vaccine specific for almost any another influenza virus," Perez said.

Most currently used vaccines offer protection for a specific animal species against a small range of virus strains. These vaccines take a long time to make (about six months for a vaccine tailored for humans) and they generally cannot be shared between species.

An Impending Human Influenza Pandemic

Avian flu viruses are so lethal to humans because they are structurally different from human strains. The human immune system does not recognize these viruses and therefore cannot defend the body against them. Because there is little natural immunity to these strains of viruses in humans, a pandemic would likely result if one of these avian flu viruses mutated to spread easily among humans. Because of increased international travel, such a virus would likely spread more easily and quickly than in past influenza pandemics.

Some avian influenza strains, including the H5N1 and H9N2 strains have shown a limited ability to infect humans who have direct contact with birds, but these virus strains cannot be easily transmitted from human to human. However, 50 percent of humans recently infected with the H5N1 strain have died, sparking growing concern among world health officials about the potential for this strain to cause a human pandemic.

The Centers for Disease Control (CDC) says another strain of bird flu virus could mutate and become easily transmissible between humans, causing another pandemic. However, no one knows which influenza strain will undergo such a mutation. The H5N1 avian flu virus has recently caused an influenza pandemic in wild and domestic birds in Eurasian and African countries, and may be a likely candidate.

"In case of pandemic influenza, we will need a vaccine, but we cannot tell ahead of time what the virus is going to look like," Perez said. "We may prepare a vaccine before the pandemic occurs, but we don't know if that vaccine is going to be good enough."

A universal backbone that could immunize many different animal species, like the one that Dr. Perez has proposed, could be modified quickly to create a vaccine for a specific virus.

"A vaccine from this backbone could be deployed much faster than one specifically tailored to humans, because the vaccine would be already available for other animals. All we would have to do is modify it, grow it, and use it in humans. We would not have to remake it from scratch," he said.

Next Steps

Perez and his team have already shown that a vaccine consisting of a weakened form of the H9N2 virus is capable of protecting chickens, their eggs and mice against two other lethal forms of the flu virus, including the highly lethal H5N1 avian flu. This vaccine could be administered to immunize wild and domestic birds against avian flu to minimize spread to humans.

Next they will test the vaccine in other mammals like pigs and ferrets, good models for the human immune system.

While it may be several years before scientists like Perez create an effective vaccine to protect humans against lethal H5N1 or other lethal avian bird flu strains, the universal influenza backbone will make the eventual creation of that vaccine much easier.