June 28, 2021 More than 2,700 dengue cases have been reported since the start of the year. The Straits Times SINGAPORE - New strains of less common dengue serotypes, which are usually imported, could raise the risk of a larger outbreak, say experts. Of the four distinct dengue virus variations, the DenV-1 and DenV-2 serotypes are most commonly seen here. The majority of infections since 2016 have been caused by DenV-2 - meaning that most recovered dengue patients would have immunity against this serotype. However, DenV-3 and DenV-4 accounted for more than half of the dengue cases sampled here since February. Last year saw the first DenV-3 outbreak here in three decades and a fourfold spike in DenV-4 cases, from 4.8 per cent of infections in January to 23.1 per cent by December.