Bird flu epidemic spurs vaccine search
twelfth victim - and unconfirmed suggestions that it may be spread
from human to human - has lent additional urgency to efforts to
develop a vaccine against the virus.
Avian flu has swept through Asia over the last few weeks and millions of birds have been culled in an attempt to stop the virus - known as H5N1 - in its tracks. Until recently, it was assumed that there were major obstacles to the disease crossing the species barrier and infecting humans. But now, the World Health Organisation is investigating a case in which two Vietnamese sisters may have caught the disease from their brother.
At the time the virus first emerged in Hong Kong in 1997, extensive studies, using both molecular and epidemiological data, eventually linked all 18 cases of human H5N1 infection to contact with live infected poultry.
The UK's National Institute of Biological Standards and Control is one of just three centres in the world working on a vaccine for the disease.
The UK researchers are constructing a vaccine by making a hybrid avian/human flu vaccine based on genetic components from both strains. A similar approach is being used by a team at St Jude Children's Research Hospital in the US and the WHO.
Using this type of 'reverse genetics,' the researchers take samples of H5N1 and mix genes from it with genetic material from a human virus, such as H1N1. H1N1 is a rapidly growing "master" strain of virus commonly used to make vaccines.
The genes from flu viruses produce antigens called HA (haemagglutinin) and NA (neuraminidase), and mutations in these antigens form the basis of the classification system. The HA gene is modified to abolish its ability to cause disease and therefore made it safer to use in the vaccine.
Once the genes are mixed together, the resulting vaccine virus produced in the cell carries both HA and NA from H5N1. But because of the alterations to HA, and the rest of the genes being derived from H1N1, the new virus vaccine cannot cause disease. Rather, it can only stimulate the immune system to respond to H5N1.
Drug therapy
Meanwhile, Roche has said that its Tamiflu (oseltamivir) drug, an inhibitor of NA, has shown activity against avian flu in preclinical studies.
Despite the lack of clinical data, the findings provide reassurance that Tamiflu can be expected to be active against any influenza virus NA enzyme subtype, including the H5N1 strain, said the company.
GlaxoSmithKline also markets an inhaled NA inhibitor called Relenza (zanamivir) for the treatment of influenza.
