Swine flu vaccines given to children during last year's pandemic have mostly minor side-effects and should provide "good protection" against infection, researchers revealed today.

The vast majority showed a "good response" in producing antibodies vital to fighting the infection in a trial of more than 900 children conducted during the 2009-10 H1N1 pandemic.

Some 98 per cent of children under three responded well to two doses of an "adjuvanted" vaccine - which contains an emulsion to boost immunity.

This vaccine - also known as a "split-virus" vaccine as the virus it is based on is broken down - was the most commonly given to youngsters last year.

Two doses of a second "whole-virus" version of the vaccine, without the booster, produced a less strong result, with 80 per cent of under-threes responding.

In children over three the difference between the two types of vaccines was less pronounced, with 99 per cent responding to the adjuvanted vaccine and 95 per cent to the vaccine without booster.

While the adjuvanted vaccine was also the most likely to produce side effects such as fever, most children affected experienced only minor reactions.

The study was a collaboration between the Health Protection Agency and the Universities of Bristol, Oxford, Southampton, Exeter, and St George's in London, assessing both vaccines for safety, tendency to cause reactions and ability to induce an antibody response.

During last year's pandemic, children were infected at four times the rate of adults and more commonly admitted to hospital with swine flu, making them a priority group for vaccination.

Matthew Snape of the Oxford Vaccine Group at the University of Oxford said today: "Children were a high priority for immunisation in the swine flu pandemic, and therefore last autumn we set out to study how well children responded to the two H1N1 influenza vaccines available in the UK."