Every year the immunization services in developing countries around the world prevent more than three million deaths from measles, neonatal tetanus, and pertussis, as well as some 490 000 cases of childhood paralysis from poliomyelitis. That achievement is due in part to the progress that numerous countries have made in properly transporting and storing vaccines and in better maintaining the cold chain that helps preserve vaccines potency.
Nevertheless, those improvements have been far from uniform, and much still needs to be done to make the best use of the available vaccine resources. With that goal in mind, the Global Programme for Vaccines and Immunization of the World Health Organization (WHO) in December 1998 issued a new publication, Thermostability of Vaccines. It is an updated version of a 1989 WHO guide entitled Stability of Vaccines.
Doubts often arise as to whether or not to use stocks of vaccines that have been exposed to elevated temperatures for some period of time. Further, there is no easy, inexpensive method that can be used in the field to answer that question. Nevertheless, a knowledge of the stability of particular vaccines can help determine storage requirements and whether or not particular stocks should be used.
And that knowledge base has expanded greatly in recent years, particularly in comparison to periods in the past when all that was available was one fairly rigid set of guidelines for vaccine-handling worldwide. While that approach offered the benefit of simplicity, it led to a dogmatic view of the cold chain and prevented local health workers from making the best use of the actual heat stabilities of different vaccines. In addition, improvements in vaccines in recent years have made them more stable.
The stability of vaccines varies widely. Diphtheria and tetanus toxoids and hepatitis B vaccine have the best resistance to elevated temperatures; freeze-dried measles, yellow fever, and the BCG tuberculosis vaccines are in the middle; and oral poliomyelitis vaccine is the most fragile. Reconstituted vaccines against measles, yellow fever, and tuberculosis (BCG) are unstable and should be used as soon as possible after being reconstituted.Even with the most-stable vaccines, exposure to elevated temperatures results in some degradation. Table 1 provide guidelines for the vaccines that are most commonly used in national immunization programs, and Table 2 gives recommendations for other bacterial and viral vaccines. Of course, all vaccines should also be handled and used in line with their manufacturers storage recommendations and expiry dates.
La termoestabilidad de las vacunas
|En años recientes, muchos países han avanzado en el transporte y almacenamiento adecuado de las vacunas y han mejorado la cadena fría que ayuda a conservar su potencia. No obstante, estas mejoras se han producido de manera muy poco uniforme y aún falta mucho para que se aprovechen al máximo las vacunas disponibles. El conocer la estabilidad de ciertas vacunas puede ayudar a establecer las condiciones en que deben almacenarse y a saber si determinados lotes deben usarse o no. En este trabajo se presentan dos cuadros donde se resumen muchos datos actualizados sobre la termoestabi li dad de las vacunas, según informa una nueva publicación de la Organización Mundial de la Salud.|
1 Based on: World Health Organization, Global Programme for Vaccines and Immunization. Thermostability of vaccines. Geneva: WHO; 1998. (Publication WHO/GPV/98.07). Available from: http://www.who.int/gpv-documents/. Accessed 14 May 1999.