Punjab, Sept. 30 -- A national surveillance study has found all four dengue serotypes circulating simultaneously across eight states and union territories. That finding arrives just as India prepares a vaccine rollout, and it changes what the rollout has to do.
Why four serotypes is the whole problem
Dengue has four distinct types - DENV-1 to DENV-4. Infection with one gives lasting immunity to that type and only brief protection against the others.
Worse, a second infection with a different serotype carries a substantially higher risk of severe dengue, through a mechanism called antibody-dependent enhancement. The antibodies from the first infection help the second virus enter cells rather than blocking it.
This is why dengue is the ra...