| Popis: |
Due to the intensive use of Sabin attenuated oral poliomyelitis vaccine, the incidence of poliomyelitis is continuing to decline, particularly in the Americas and Western Europe. In some developing countries, the use of trivalent attenuated vaccine may, however, sometimes produce sub-optimal antibody responses. Moreover, rare cases of vaccine-associated paralytical poliomyelitis could become increasingly prevalent, especially in countries that achieve control of the wild-type polioviruses. Recent progress in understanding the molecular biology and mechanisms of attenuation of polioviruses has suggested several possible approaches to solving some of these problems with improved attenuated poliovirus strains. During WHO meetings discussions took place on the broad scientific and ethical criteria that would justify submitting new attenuated oral poliomyelitis vaccine candidates to different levels of testing in laboratories and in humans. |
