As per Islam we are ordered to seek out cures and treatments...
I find that hard to believe a scientist said that vaccinations are harmful.
While it is true some types 0f vaccinations are harmful,,, there are two types of vaccinations if I recall. One type of vaccination takes the proteins and DNA of bacteria and viruses and they inject these into the bloodstream of an unvaccinated patient. In this case, there is no danger because the bacteria and virus are not live, but dead (although there may be some cases where there is a mistake, very rarely, where a live microbial may be injected, and even then it is still not that dangerous because of your immune system).
There are vaccines that inject live bacteria/viruses into the blood stream (or even toxins for example) because this will produce a longer and more effective immune response and there is risk in that although it would be in a control environment.
The purpose of the injection is to get your beta memory (B cells) to analyze and memorize these bacteria/viruses and thus instruct the immune system to create cytotoxic T-Cells to combat these bacteria/viruses. In cases where live mirocibials are not injected, and just the proteins or dna is injected, the T-cells will take action against a lifeless microbial. The B-cell will keep the injected microbial memorized and if you should ever get attacked by this type of microbial again in an uncontrolled setting and in a case where the microbials are alive, then your B-cells have already seen this type of intruder and they will instruct the t-cells to quickly take action.
and when the immune system responds to a vaccine as mentioned above, you may feel symptoms of illness such as fever for example, but that is a sign of your immune system responding to the vaccine which will help later on if you should ever come into contact with the microbial, it doesn't mean you are dying.
The reason why unvaccinated people are safe sometimes,,,, is because vaccinated people around them act as a shield to ward off microbial, so if unvaccinated individuals did not hang around vaccinated individuals then their chance of illness would increase (i.e. like the flu for example, the flu has many different strands and there is always a new type of flu every year hence why we get new flue shots).