A second example of the protective role of heterotypic dengue neutralizing antibodies was observed in 1995, when dengue 2 (American genotype) was introduced into Iquitos, Peru, a city of 300,000 on the Amazon River. Previously, dengue 1 had been endemic. Serial infections with dengue 1 then 2 in Cuba in 1981 had resulted in a large outbreak of DHF/DSS. In Iquitos, 60.5% of the population were infected in the sequence dengue 1 then dengue 2.