Why do you need two doses of the GSK vaccine

[dikkertjedap]

I read that you might only need one dose of the Novartis vaccine but understand that the NHS is still planning that people need two doses of the GSK vaccine. Any idea why this is and would it not be better than to try to get the Novartis vaccine (assuming that it is possible to obtain it). Any thoughts?

Not a simple answer, I'm afraid... but the GSK vaccine is likely to work at one-dose schedules. I've not seen the Novartis data.

Based on the H5N1 (avian) vaccine trials, one 'standard' dose of the 3.75ug GSK swine flu vaccine (Pandemrix) is likely to seroconvert (i.e. generate significant antibody response) in ~45% of people aged 18-60. There has been one investigational study using 5.25ug (roughly double antigenic dose) of H1N1v where >98% 18-60y seroconverted, but obviously that vaccine dose is not available.

As far as I can see there are no one-dose results for children aged 3-9y or the elderly 60-80+.

Results for two doses, given at 0 and 21 days are:
~100% of children 3-9y
~95% of people aged 18-60y
~85% of people aged 60-80+

You can see how much better the two-dose schedule works. Remember a single dose may provide some immunity to start with but there's little evidence that it will last as long as that given by a two-dose approach.

Thanks, but where did you find this data? Also, I have just done some more searching and found this on the GSK's website:

GSK press release of 14 September 2009

"This trial provides encouraging data on the potential use of a single dose of our pandemic vaccine." said Jean Stephenne, President GlaxoSmithKline Biologicals."

So why two doses on the NHS?

My main concern would be that a too high dose could cause a cytokine storm especially in vulnerable groups.

Yes that's the data on the higher 5.25ug dose, which is not the formulation (3.75ug) that had to be ordered by the DoH in time to get the deliveries for the winter.

Getting enough vaccine to immunise the population has a long lead time, but trials are still going ahead and the information coming from them will guide how vaccines are used in the future. It may be that a single dose of higher antigen concentration becomes recommended, but higher antigen dose can sometimes mean more adverse reactions.

The GSK data information used by the EMEA is here:

www.emea.europa.eu/humandocs/PDFs/EPAR/pandemrix/Pandemrix-PU-17-en.pdf