Surveillance of suspected poliomyelitis in Albania, 1980-1995: suggestion of increased risk of vaccine associated poliomyelitis

Abstract

Surveillance of suspected poliomyelitis cases was conducted in Albania from 1980 through 1995. A total of 93 cases were reported, 11 of which were clinically defined as poliomyelitis cases according to WHO criteria. Poliovirus was isolated from six subjects who were defined as contact vaccine-associated cases. Characterization of isolates by both antigenic and molecular methods showed that, in all cases, the disease was associated with type 2 or 3 polioviruses of vaccine origin with retromutations known to be associated with loss of Sabin attenuated phenotype. Infection occurred despite the fact that all patients had records of previous immunization with oral polio vaccine (OPV), suggesting a failure of vaccination. Four of the five patients from which poliovirus could not be isolated were classified as possible recipient vaccine-associated poliomyelitis on the basis of serology data (presence of antibodies against all three polioviruses) and the temporal association between the latest dose of vaccine received and onset of paralysis. Virological investigation on healthy contacts of the poliomyelitic patients yielded the isolation of a further 12 Sabin-like polio revertant viruses, mostly type 2 and 3. A detailed study of the non-polio acute flaccid paralysis (AFP) cases and their healthy contacts revealed the presence of several enteroviruses, namely Echo, coxsackie and, in three cases type 2 or 3 Sabin-like polioviruses. Overall, these data suggest the absence of circulation of wild-type poliovirus in Albania from 1980 to 1995, before the recent outbreak of poliomyelitis in 1996, and emphasize the need for active surveillance of AFP and laboratory characterization of virus isolates to monitor vaccination efficacy.