TABLE 2.

Proportion of strains with recombinant genomes among VAPP case isolates in Romania, 1980 to 1990

Polio-vaccine serotypea	RFLP assayb		Category of recombinant (genotype)c	No. of strains (% of recombinants)	Total no. of strains	% Recombinants in each serotype
	1 + P2	3D1 + 3D-3′
S1	S1	S1	∼∼S1∼∼	5 (0)	5	0
	S2	S2	∼∼S2∼∼	9 (0)	9
	S2	S3	S2/S3	9 (23)
S2	S2	S1	S2/S1	24 (62)
	S2/S3	S1	S2/S3/S1	1 (2)	39	81
	S2	W	S2/W	5 (13)
	S3	S3	∼∼S3∼∼	7 (0)	7
S3	S3	S1	S3/S1	9 (32)	28	80
	S3	S2	S3/S2	19 (68)
Total			Sn/Sn + S2/W	67 (76)	88d	76

^aS1, S2, S3, Sabin PV vaccine-derived type 1, 2, and 3, respectively. 

^bCharacteristics of the genomes according to RFLP assays 1 and 3D1. In some cases, RFLP P2 and 3D-3′ assays were also used (see Materials and Methods). S2/S3, intertypic recombinant genome in which the 5′ part is derived from S2 and the 3′ part is derived from S3; W, wild (non-vaccine). 

^cSn, Sabin strain of any serotype; ∼∼S(n)∼∼, nonrecombinant Sabin strain; S2/W, V/W recombinants. 

^dThe analysis is based only on the 88 strains isolated in Romania during an 11-year period (1980 to 1990).