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Double dose needed to protect against flu pandemic

09/10/2008

People will need to be vaccinated against the next influenza pandemic twice, a UK-led report said on Thursday.

A research team from the University of Leicester, supported by scientists from the US and Germany, said patients vaccinated for the first time needed two doses to achieve the required protective level of antibodies after six weeks.

An influenza pandemic occurs when a new influenza strain emerges - one to which humans have no immunity - mutates and spreads globally as a virus.

Although it is not possible to predict the actual pandemic influenza strain, global health authorities have identified H5N1 avian influenza as a strain with the greatest pandemic potential in humans.

H5N1 is currently circulating in birds and has caused serious illness in more than 380 people worldwide with a mortality rate, among people known to have been infected, of greater than 60 per cent.

Writing in the New England Journal of Medicine, study author Dr Iain Stephenson of the University of Leicester said: "It generally takes two doses of vaccine to give a good response, so if a pandemic occurred it would take some time to produce vaccine and then administer two doses to protect people.

"Therefore stockpiling of vaccines has been suggested to overcome some of these difficulties. However, subjects will still require two doses to generate protection and if the pandemic spreads rapidly this could be challenging to deliver."

The Leicester study looked at boosting those people who were vaccinated up to seven years ago in the first H5 vaccine trials with a new updated H5 vaccine, in comparison to vaccinating subjects for the first time.

It found that of those given a single low dose booster vaccine, 80 per cent of people had an excellent response to H5.

The results indicate that regardless of which avian strain individuals are originally primed with, they are quickly protected against a broad range of avian strains following their booster vaccine, even strains they were not initially inoculated against.

These results potentially provide a rationale to prevent pandemic influenza by proactively immunising the public with stockpiled pre-pandemic vaccines.