Background:
Dengvaxia was used in the Philippines to vaccinate 9-10-year-old school children, living in areas highly endemic for
dengue. After about 830,000 had received at least 1 of 3 recommended doses, risks of enhanced disease in
dengue-naïve vaccinees were reported. Methods: We used Phase 3 trial data to derive the proportions of cases of hospitalised and
severe dengue that might have been prevented by the Philippines vaccination programme and, among those cases that may occur in vaccinees, what proportions are likely to arise in those who were seropositive or seronegative for
dengue at the time of first vaccination and what proportion in the latter group may be enhanced disease attributable to the
vaccine. Results: Assuming about 15% of vaccinees were
dengue naïve at vaccination and the effects of the
vaccine are independent of the number of doses received, we estimate that, in the 5 years following vaccination, the number of cases of severe disease in the vaccinated population will be reduced by about 70%. Among vaccinees who do develop severe disease, about half the cases will be due to
vaccine breakthrough in seropositive vaccinees, and about a quarter will be excess cases in seronegative vaccinees that will have occurred as a consequence of vaccination. Conclusions: Overall, the Philippine
dengue vaccination programme will likely prevent a substantial number of
severe dengue cases and, among those that do occur, the majority are likely to be breakthrough disease in seropositive vaccinees and a minority attributable to the excess risk of enhanced disease in seronegative vaccinees.