The recombinant vaccine for H5N1 and H7N9 were made by inserting a bit of the virus into the Newcastle virus vaccine. Reuters

Kansas State University researchers have developed vaccines for two strains of avian influenza that can be transmitted from poultry to humans.

The vaccines for H5N1 and the deadlier H7N9 were made by combining two viruses to create a recombinant vaccine.

Both the strains have seen the culling of millions of chickens and turkeys besides causing the deaths of hundreds of people.

A vaccine strain of the Newcastle disease virus that naturally affects poultry was cloned and a small section of the H5N1 virus placed into it, creating a recombinant virus. The new recombinant virus vaccinated chickens were protected against both Newcastle disease virus and H5N1.

Researchers similarly inserted a small section of H7N9 into the Newcastle vaccine to produce an effective vaccine against the strain.

"In contrast to the H5N1 virus that kills the majority of chickens in three to five days, chickens infected with the H7N9 virus do not show clinical signs of sickness," noted Jürgen Richt, Regents distinguished professor of veterinary medicine and director of the US Department of Homeland Security's Center of Excellence for Emerging and Zoonotic Animal Diseases.

Various emerging strains
The H5N1 strain has been most active in Indonesia, Egypt and other Southeast Asian and North African countries. More recently, it has been among the many strains spreading across the US.

Since December almost 34 million birds across 15 states in the US have died or been killed because of one of three avian flu strains: H5N2, H5N8 or H5N1.

It is only the H5N1, H7N3, H7N7, H7N9 and H9N2 that infect humans.

There have been nearly 650 cases of H5N1 human infections, reported from 15 different countries since 2003.

The subtype H7N9 is a deadlier strain circulating in China since 2013. It swaps genes with other types of flu viruses, giving rise to new strains. Any of the new strains could start a pandemic.

The World Health Organisation had voiced concern about avian influenza noting that the diversity and geographical distribution of influenza viruses currently circulating in wild and domestic birds is unprecedented. "The world needs to be concerned," it said.

The latest work on vaccines has been published in the Journal of Virology study, "Newcastle disease virus-vectored H7 and H5 live vaccines protect chickens from challenge with H7N9 or H5N1 avian influenza viruses."

Puzzling spread in US
Meanwhile, researchers in the US continue to be perplexed on how the bird flu virus is spreading across the country.

Labs in Minnesota recently detected H5N2, a mixed-origin avian flu that had never been seen in the US before. But with tests on wild ducks and geese thought to harbour the virus turning negative, the search continues, reports Scientific American.

Surprisingly, an air-sampling study of four poultry barns in the region detected bits of genetic material from H5N2 in air particles showing the virus could be transmitted through the air, at least over short distances.

There have been confirmed cases of ducks and geese infected with the H5N2 virus through Washington, Oregon, Idaho, Missouri, Kentucky, Wyoming and Kansas. In some states there have been reports of H5N8 and H5N1 strains in waterfowl.

The H5N8 picked from Asian birds during migration probably mixed with North American avian influenza viruses to create new viruses with "H5" part of the virus from Asia and the "N" part from North America.

H5N2 and H5N1 are two of the new mixed-origin viruses.