A vaccine that could help to control a flu pandemic has shown encouraging results in its first human trials.

The vaccine, made by Acambis, based in Cambridge, should protect against all strains of influenza A, the type responsible for pandemics. Unlike existing vaccines it does not have to be reformulated each year to match the prevalent strains of flu, so it could be stockpiled and used as soon as a pandemic strain emerges. Nor does it need to be grown on fertilised chicken eggs, as the existing vaccines do, but can be produced by cell culture.

The results, announced yesterday by Acambis, show that in human volunteers the Acam-Flu-A vaccine was safe and produced an immune response against its target, a small protein (peptide) called M2e that is found on the surface of all A-strains of the flu virus. The vaccine was also tested on ferrets, which are commonly used in flu research because they are susceptible to human and bird flu.

The ferrets were divided into two groups and either vaccinated with the new vaccine or left unvaccinated. They were then exposed to a large dose of the H5N1 bird flu that has killed millions of chickens and more than 200 people across Asia since 2003. All the unvaccinated ferrets died, but 70 per cent of the vaccinated ones survived.

A significant problem with conventional vaccines is that they attack parts of the flu virus that can change rapidly. Each season the World Health Organisation identifies the three strains that are circulating, normally two A-strains and one B, and the vaccine is made to order to provide protection against them. It is always a race against time, because millions of eggs have to be produced to grow the vaccine and if it is not used it is out of date by the following season.

Acambis’s approach was to identify some aspect of the virus that is unchanging. Pandemics are invariably caused by A-strains of flu; B-strains, which are found only in humans, may cause epidemics but have never caused pandemics.

The company identified a peptide, M2e, on the surface of all A-strains and developed a vaccine that targeted it. When an individual is vaccinated the vaccine teaches the immune system to recognise and be alert to the peptide so that as soon as flu arrives the body’s protective systems swing into action against it. To improve the vaccine’s effectiveness, it was combined in the trial with adjuvants, chemicals that ginger up the immune system and improve its ability to learn. The adjuvant called QS-21, made by Antigenics, proved to be the best. When this was added, 90 per cent of those vaccinated had antibodies against the M2e peptide.

Michael Watson, the executive vice-president for research and development at Acambis, said: “If there was an immediate threat of pandemic flu, it would be possible to complete the trials and market the vaccine within three years. Without such a threat, it will likely take longer, perhaps five years.

“The beauty of the vaccine is its simplicity. It could be used in several different ways. First, we could produce a pre-pandemic vaccine that we know would be effective against A-strains. If a bird flu strain such as H5N1 turned into a pandemic strain we could get the vaccine out of storage and use it. Alternatively we could use it as soon as we got the slightest inkling of a pandemic strain emerging. Or it could be used instead of the normal vaccine for protecting against seasonal flu, with a vaccine against B-strains added. That would depend on how effective it was, which we will only know after further trials.”

The fate of millions

— Flu viruses can drift and shift. Drift refers to the continual small changes that dictate the annual reformulation of the flu vaccine to ensure that it works. Shift happens rarely and unpredictably, and produces pandemics

— There were three shifts in the 20th century, causing pandemics in 1918, 1957 and 1968. Some virologists fear that another is overdue

— Pandemic strains strike human beings unprepared, and spread fast. The 1918 pandemic killed 20 million, some say 40 million

— Shifts occur when avian strains infect human beings, or avian and human strains share genes, as may be happening in Asia

— Since the H5N1 avian strain first appeared in 2003, a few hundred cases have been transmitted to humans. About half of those have died, but this is not yet a pandemic strain, and may never become one

Source: Times database

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