The "leaky" vaccines protect the vaccinated individuals but don't prevent the transmission of infection to others as well as pave way for evolution of much virulent strains of pathogens, reports a study published in online journal Public Library of Science Biology.

The researchers studied the concept with the help of a herpes virus strain that infects chicken. The "leaky" vaccine against Marek's disease was observed to have prevented the vaccinated birds from death, but they remained a reservoir of infected pathogens and transmitted the infection to other unvaccinated birds, which reportedly died, according to Belfast Telegraph.

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British investigator Professor Venugopal Nair, from The Pirbright Institute near Woking, Surrey, said: "Our research demonstrates that the use of leaky vaccines can promote the evolution of nastier 'hot' viral strains that put unvaccinated individuals at greater risk."

Vaccines like that of polio, mumps, smallpox, rubella and measles are termed as "perfect" because they protect the vaccinated individuals as well as prevent the transmission of infection from the vaccinated one to unvaccinated one, reported The Australian. The "leaky" vaccines on the other hand protect the vaccinated person from the disease with some mild symptoms but remain contagious. Such a "leaky" vaccine used in the bird flu though protected birds threw human population at risk, reported the researchers.

Professor Andrew Read, the co-author of the study from Pennsylvania State University in the US, said: "We humans never have experienced any contagious disease that kills as many unvaccinated hosts as these poultry viruses can, but we now are entering an era when we are starting to develop next-generation vaccines that are leaky because they are for diseases that do not do a good job of producing strong natural immunity - diseases like HIV and malaria," according to Mirror.

Read noted that it is very important to be cautious that Ebola vaccine under development should not be "leaky" because such a vaccine might turn out to be a bigger threat than the disease itself.

Professor Adrian Hill, director of the Jenner Institute at Oxford University, said that there is no evidence indicating the evolution of virulent strains of pathogens on vaccination in humans by far. He also noted "leaky" vaccine in bird flu shouldn't be taken as an example for other human vaccines.

Tagsvaccines, "leaky" vaccines, HIV