Simultaneous vaccination against seasonal and pandemic flu provides protection against the virus without provoking significant side effects, according to a clinical study released on Monday by GlaxoSmithKline.

The research – requested by regulators and keenly awaited by governments tackling the current H1N1 “swine flu” pandemic – should ease international concern about the provision of both vaccines and help accelerate vaccination programmes.

It comes at a time when vaccine manufacturers including GSK have struggled to meet demand, with production of the pandemic vaccine proving slower than anticipated, while a second wave of virus is already well under way in countries including the US. Initial doses on any scale have only become available in the past few weeks.

In an analysis using its Pandemrix and Fluarix vaccines conducted on 168 adults aged over 60, GSK, the UK-based group, showed both good tolerability and immunogenicity (protection against the virus) when injected into separate arms at the same time.

The study did not analyse the effects of the vaccine in younger children, who have been disproportionately affected by the pandemic virus, nor did it compare directly whether the two vaccines jointly provided a any more protection against different types of flu than a single vaccine.

However, it served to cast further scepticism on initial reports this autumn from Canada – which have yet to be published in any medical journal after scrutiny by peers – suggesting one vaccine could negate the effects of the other.

It also helped confirm existing official advice from SAGE, the World Health Organisation’s expert committee, arguing in favour of providing both vaccinations simultaneously.

Some countries, such as France, currently recommend giving seasonal and pandemic vaccines, but staggering them by three weeks. That risks creating additional burdens on already stretched healthcare staff.

Other public health specialists have cast doubt on the Canadian reports, with the US Centres for Disease Control and Prevention saying it found no such evidence and advising in favour of both seasonal and pandemic vaccinations.

Last month, the University of British Columbia also registered its intention to conduct a detailed study analysing the relative effects of seasonal and pandemic vaccines, but it does not expect to have findings for at least another year.

GSK said there had been some reports of pain, swelling, redness, fatigue, muscle ache and low level fever in those vaccinated in its trial, but within the limits judged acceptable by regulators for each of the products approved and given separately.