A Shot for All

A vaccine in the making — equally effective for birds, men and other mammals — offers a shield against another outbreak of bird flu.

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Of all the viruses that can cause a devastating pandemic (worldwide outbreak), the influenza virus is the most likely to cause one. Influenza is a tricky disease to control. The world has already seen several outbreaks, of which the influenza pandemic in 1918 was the most serious: at least 20 million people died all over the world then. There were pandemics in 1957, 1968 and 1977, but of much less severity.

Recently, avian influenza (or bird flu) has emerged as a candidate that can cause a serious pandemic. Experts warn that another outbreak is imminent and we have only limited ability to control it if one breaks out. However, several vaccines — now in the laboratory stage — offer hope.

One of the problems of bird flu is that it affects birds as well as humans and other mammals. The virus may be slightly different in each of the animals, and it is difficult to give different vaccines for different animals during a pandemic. At the Department of Veterinary Medicine in the University of Maryland in the US, Daniel Perez and his colleagues have developed a vaccine that can control the disease in birds, humans and rodents. It is based on a region of the virus gene that is common to all the strains. “We have shown that the vaccine works in rodents and does not cause the disease,” says Perez.

This vaccine has been tested in rats but not yet in humans. Meanwhile, at the University of Pittsburgh medical college, scientists are testing a vaccine against the deadliest of all avian flu viruses, the H5N1. This is a genetically engineered vaccine that takes only 10 weeks to manufacture. The other vaccines now in the market are made using chicken eggs, and take several months to manufacture, apart from not being able to provide enough immunity. Two months ago, the institution received a $3.6 million grant to test the vaccine in non-human primates.

Currently, three companies manufacture vaccines against the avian flu virus H5N1, all of them approved in different countries in the last year and a half. Sanofi Pasteur’s vaccine was approved in the US in 2007, GlaxoSmithkline’s vaccine was approved in Europe in May this year. Australia approved a vaccine from CSL Limited. All of them are live attenuated virus — which have been so altered that they can’t cause disease — raised on chicken eggs. While all of them provide some protection, none of them can prevent a pandemic. This is because the virus mutates fast, and we do not know what strain of the virus would be involved in a pandemic.

One of the known — and fortunate — facts about the bird flu virus is its specificity. The virus that infects birds does not easily infect humans. This is why many outbreaks in birds have not resulted in human infections. Which is probably also why human to human transmission has not happened in large numbers so far.

However, such a transmission is not scientifically impossible. Since the virus mutates fast, strains of broader range can emerge. They can infect humans, pigs, rats, birds and other animals. It would be difficult, if not impossible, for us to make different vaccines for different animals. The Maryland University team has shown that it is possible to make a single vaccine effective in many animal species.

This vaccine is based on a DNA backbone that is common to all the strains. This backbone lies inside the virus and not outside. The scientists have a strain of the virus called WF10 with this backbone. They have isolated other influenza viruses that are related to this strain, including the human influenza virus. They had earlier shown that by tweaking the gene of this strain they could make a vaccine effective in birds. Now they have shown that, by further modification, this strain can protect many species against the influenza infection. In particular, they have shown that it provides protection in rats against H5N1, the most lethal strain against which human vaccines are made. Says Perez: “We have done animal trials, but we are yet to do human trials.”

There are other developments that could help in preventing a major pandemic. A series of DNA vaccines against H5N1 are also under development in several institutions. They are the Virology Research Institute in Maryland, which began clinical trials last year, the University of Pennsylvania School of Medicine, and the Rockefeller University. A DNA vaccine is a piece of DNA that can directly make the protein that produces an immune response. It is safe, because it cannot by itself cause the disease. The vaccines can be made rapidly, which is invaluable in case of an epidemic.

However, there are technical issues, which all these teams claim to have solved. If they work, we could soon have a vaccine that can be rapidly made when there is an epidemic. Let us wait and watch their progress.

Sources: The Telegraph (Kolkata, India)


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