Which of the following dengue sequential serotypes infection are associated with maximum risk of dengue hemmorhagic fever?

Studies in Thailand have revealed that the DENV-1/ DENV-2 sequence of infection was associated with a 500 fold risk of DHF compared with primary infection. For the DENV-3/DENV-2 sequence the risk was 150-fold, and a DENV-4/DENV-2 sequence had a 50-fold risk of DHF. There is no time-limit to sensitization after a primary infection. The 1997 Santiago de Cuba epidemic clearly demonstrated that with the introduction of DENV-2, DHF had occurred 16-20 years after the primary infection with DENV-1.