A new research by the University of Leicester warns of a six-month time lag before effective vaccines can be manufactured in the event of a pandemic flu outbreak, a British vaccine expert said on Tuesday.

"If an influenza pandemic occurs, vaccination will have to be the main way to protect the population," said Iain Stephenson, consultant in infectious diseases at the Leicester Royal Infirmary and a clinical senior lecturer at the University of Leicester.

"Unfortunately, if a pandemic occurs, it will take up to six months to manufacture effective vaccine, so the first waves of the pandemic may be over before people are vaccinated," he said.

"To reduce any delay, we could consider stockpiling vaccine or immunizing people with vaccine prepared in advance, in a so-called pre-pandemic vaccine against a future pandemic," the expert said.

Stephenson and his team conducted a study comparing the effect of a single H5 bird flu vaccine dose to people who had been vaccinated with an H5 vaccine previously with people who had not previously received vaccine.

"This study means that we could vaccinate people potentially many years before a pandemic, to generate memory cells that are long lasting and can be rapidly boosted by a single dose of vaccine when needed," he said.

However, people still don't know which strain of influenza will cause the pandemic, as there are several strains of H5N1 virus, Stephenson said, adding that a pre-pandemic vaccine needs to give cross protection to as many H5 strains as possible.

A vaccine on swine flu needs more study, he said.

(Xinhua News Agency April 28, 2009)