POST 00419E : PROTECTION OF MORE COLD-SENSITIVE VACCINES

POST 00419E : PROTECTION OF MORE COLD-SENSITIVE VACCINES Follow-up on Post 00391E, 00400E and 00412E 30 January 2002 __________________________________________________________ Watching the debate on the protection of more cold sensitive vaccines unfold, Ian Wyllie of the University of Southampton thought that referring to the findings of the work he is currently engaged in would be potentially of interest. here is his contribution : "I note that this subject is surrounded by complex practical, political and occasionally interesting thermodynamic arguments. Disregarding all these, the problem on the ground remains: At clinic level vaccines are frequently exposed to temperatures below 0°C. The critical question is: is this undesirable? The balance of opinion appears to be that it probably is, and there has been much written (rightly) about the high ethical principles which should be pursued in the delivery of the EPI. EXAMINATION OF THE ORIGINAL PAPERS SHOWS THAT THE SCIENCE IS EQUIVOCAL: Therefore, because lives and millions of dollars turn on this opinion, would it not be wise to fund some significant study, at some significant university with an interest in vaccine development? I understand that it is probable that a well-designed animal study could give an answer beyond reasonable doubt. Accepting that as of today it is considered undesirable then what can be done? If damage to antigens is proportional to time at below the limiting temperature, or indeed if it is proportional to the number of "instantaneous" exposures to temperature below the limiting temperature, then: CONDITIONING WILL HELP TO REDUCE VACCINE DAMAGE This being so, how can conditioning be implemented rapidly in the field? By mandating the production of shell texts for translation: * addressing the prevalent thermodynamic ignorance - i.e. an ice pack at -10°C is NOT 10 times more effective than one at 0° C. * providing a protocol for arranging for adequate conditioning. * providing an explanation of the implications for those using stored cold refrigeration in remote areas: that conditioning will reduce the cold life to some degree, and that an approach to combat this is: 1) to store vaccine and conditioned icepacks in one cool box and 2) ice (alone) at -10°C to -20°C in another conditioning and using the deep frozen ice as required. This could be done, and undergo initial trials in 60-90 days from the start date. It would be an economically appropriate and, fashionably, a S.M.A.R.T intervention. REFERENCES TO COLD WATER PACKS The references to cold water packs are indefensible. They will not work. The reason that icepacks work in cooling is because the ice requires an enormous amount of energy to change from ice to water. This energy has to be supplied from the environment. It is known as latent (hidden) heat, because no change in temperature is observed while the ice is changing from ice to water. If the environment is the interior of the cool box, then this latent heat is supplied to the ice from the interior of the cool box. This (with the numbers of icepacks specified by EPI) reduces the temperature of the interior of the cool box until it is equal to that of the melting icepack. (0°C). Cold water however heats up linearly, and therefore has a minimal cold life. If it is necessary / helpful then we could produce a very basic guide to the engineering physics of what is going on here for TECHNET members. Just ask, - it would take about 30 days. A BROADER SOLUTION More broadly, the effective solution to this problem is to encourage the introduction of effective independent refrigeration. Politically, I observe, this is a difficult area. From an engineering perspective the most logical answer is: * A vapour compression system * Providing capacity for the extremely limited storage needs at clinic level (observed to be in most cases = 30°C ambient temperatures. The extremely significant science being done with respect to malaria and HIV vaccines particularly at Oxford UK, is not concerned with preservation technologies - and rightly so. Their concern is to do good science quickly. Therefore there is no guarantee that the vaccines that we all hope they produce will not require cold chain. Surely ethically the public health community could not exclude effective solutions, simply because they did not conform to the available delivery mechanism. Finally, if the supply of independent refrigeration benefits local economies over the next 10 years until thermostable vaccines are in global use, then the disturbance to those markets caused by international donation of equipment may be dissipated, and local capacity for medical refrigeration will have been built into the economy. Ian Wyllie works on Design Study on Medical Products Refrigeration for Use in Relief and Development Settings at the Faculty of Engineering and Applied Science, University of Southampton, UK. Hans Everts < mailto:[email protected] > contributes the following comments : “ The way out for the freezing problem lies not solely in technological, managerial or operational solutions, but in a combination of them. Technological solutions should be based on the long term necessity to simplify the cold chain. However, I insist that solutions should be based on good knowledge of the impact of marginal freezing on the immune response. Marginal does not mean irrelevant, but refers to freezing in equipment that is not meant to freeze: refrigerators and cold boxes. The problem of freezing cold-sensitive vaccines in a freezer is a totally different issue. At this point we do not have that knowledge. Proposed solutions can be looked at in 2 ways: 1) solutions that are useful anyway, irrespective of the freezing problem, i.e. taking vaccines out of the cold chain, solar refrogerators or electronic thermostats. 2) solutions that lead to a change of practices specifically to cope with the freezing problem, i.e eutectics, cold packs. I am quite concerned about the second type. Introducing all kinds of new practices to deal with a freezing risk will for a considerable period lead to a lot of confusion. We simply do not know if the impact of freezing on the immune response justifies this confusion. As mentioned in previous messages, manufacturers have been asked to ensure that no negative temperatures occur anywhere during the tests of new equipment. All manufacturers have complied. Some have installed racks to prevent storage against the evaporator. Surely this is not enough, since it then all depends if people really use the baskets supplied some chest model appliances, or if people set the thermostat at a maximum. However, it would be worthwhile to see if these changes have any impact at all. Feedback from countries that have recently received equipment would be much appreciated.â€