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Half-dose flu vaccines as effective as full strength jab

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Half-dose flu vaccines are as effective as full-dose vaccines for those under 50, according to a study.

The report found that those younger than 50, who had previously had a flu jab, did not have a substantially different immune response to a half-dose than a full-dose vaccination. This means that a half-dose vaccine could be used in times of vaccine shortage.

US researchers carried out a randomized clinical trial of healthy adults aged 18-64. Between November and December 2004, 554 adults were given a full-dose of flu vaccine, and 556 were given a half-dose.

Blood samples were taken 21 days after vaccination. They showed that antibody responses in the half-dose patients were not substantially inferior to the full-dose, particularly in those aged 18-49. Women of all ages had a greater response to both doses than men.

Report authors said: ‘As recommendations for influenza immunization expand and evidence that elderly persons (men older than 60 years) may require higher doses of vaccine for optimal responses, reduced doses in healthy, younger populations may become a valuable national strategy.”

Archives of Internal Medicine (2008) 168: 2405-2414

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