Table 2. Serum neutralization of ancestral sylvatic dengue virus isolate D1/Malaysia/36046/05, Malaysia*.

Serum group*	Neutralizing antibody titer†
Mock	0
Virus	0
Medium	0
SI	320
SII	80

*Mock, controls treated with serum from healthy (no dengue infection) donors; virus, virus plus diluent; medium, serum and diluent without virus; SI, subgenotype I; SII, subgenotype II.
†Reciprocal of the highest serum dilution that reduced viral foci by 50% (50% focus-reduction neutralization test). Serum from patients infected with sylvatic virus was not available. Virus was treated with serum from patients infected with primary dengue virus type 1 SI or SII.