The risks of potentiation of disease with vaccinating children and adolescents against COVID is fundamentally different than the risks with Dengue. The reason is that they are infections acquired in very different manners.
Dengue is contracted by transmission from mosquitos. Even if you were to vaccinate an entire population, unless you kill all the mosquitos or prevent the mosquitos from carrying the disease, people will continue to be exposed. Therefore, breakthrough cases will continue to occur, and the frequency of which will be unchanged regardless of how many folks are vaccinated.
COVID is an infection transmitted primarily from person to person (unless you are an Ozzy Osbourne impersonator and chomping on a bat’s head). As the vaccine is clearly lowering the ability to contract the virus, the more people that are vaccinated, the less vectors for transmission. Even in the case where everyone is vaccinated, there still may be low level transmission of the virus in society. Severe disease in adults would rarely occur in such a situation. In the case of adolescents, if transmission in society was lowered markedly by a vaccination campaign such as is ongoing, even if potentiation were an issue, it may be irrelevant. Reason being that the reduction in numbers of adolescents ever being exposed would minimize the number who could suffer a breakthrough infection and experience a worse outcome due to being vaccinated. Keep in mind adolescents can have bad outcomes from COVID. While death is rare, they get “long-haul” infections much as the adult population. The theoretical risk therefore is expected to be offset by the benefit they are known to receive.
This is where I get a bit philosophical on you. We all have a mutual responsibility to one another. That means taking on some risk now and again on behalf of others. We are not talking about running across the train tracks to save someone from the oncoming train. Imagine how our society would function if we didn’t. I am sure you like your electricity. For you to have it, there are folks willing to risk their lives. Most of us never give it consideration, but I know someone who was shocked off one of the lines suffering severe burns doing just that. Works out great when you accidentally set your house on fire and folks come to put it out rather than letting it burn to the ground? How about the lifeguard who heads out to try to pull the drowning, thrashing kid out of the ocean at the peril of get pulled under by them? How about taking a shot that was already given to several hundred million adults without significant concerns and a ton of benefit?
Regarding the question of adolescents and potentially younger children in the future, the answer lies in strategy. The goal is to eliminate severe disease, including long-haulers. We started with the elderly and high risk and progressed to vaccinate all willing adults. It is not sufficient. We will need to work backwards down the number line. Next up are our adolescents. Will we be able to stop there? Maybe. Might we be revisiting this with more data on adolescents and initial data on children in a few months. Quite probably. This needs to be taken care of before the fall when coronavirus season warms up again. The more the adults comply, the less we will rely on progressively younger ages in an attempt to reach herd immunity. Might we never achieve herd immunity? Sure. Hopefully if not, we still render the severity of what circulates to something far less significant than the current situation.