Thijs,

From what I understand from cold-chain practice and lyophilization. The lyophilized vaccine, though certainly more stable following lyophilization than if in liquid suspension, is thermally unstable over long periods of time. Keeping the lyophilized prep at 4C slows the rate of degradation. This is the same reason for why they also suggest keeping the vaccine in dark conditions as UV light can also disrupt the compounds. You can keep the prep at room temperature, however, as you have read previously, the viability of the preparation will decline more rapidly. 

Hope this helps.

Chris

Chris,

Thank you for your reply. Why would it degrade do you think? Is freeze drying not sufficient to stop enzyme activity? Thus it would require constant cooling to stop biological activity.

I'm not aware of what happens with a micro-organisme if you freeze dry it.

Thijs

My best guess is that It's probably due to antigenic proteins unfolding. Though there may still be reactive species which have been dried with the preparation and in the presence of light may react with the BCG vaccine strain. I haven't seen too much in the literature about this, however, the data certainly suggests that a lyophilized prep at room temp is far less viable than a prep kept in cold chain.

The freeze-dried BCG vaccine is much more heat sensitive that can lead to loss of potency of the vaccine if proper cold chain is not maintained.