* Are we suppose to assume the aliens have no doctors or any kind of treatment? I know its in the original novel that germs kill them, but H.G. Wells wrote it at a time when antibiotics let alone effective treatments and isolation were not known. Medical science was not really advanced at the time so Wells could not assume a future were invading armies were free of this risk. An invading army from space would have access to stuff we cannot yet conceive yet they fail to take basic precautions in an alien environment for them.
** Multiple sources from the musical adaptation of the original novel state that the aliens had wiped out any form of disease on their planet, and thus eliminated the need for medical science (at least the kind that treated infections or diseases). So they just didn't think to prepare, or their immunity was ''that'' low after centuries of not facing infections at all that they were all terminal before they could get anyone to research a cure.
** The book also mentions that the aliens wiped out all disease and germs on Mars, leaving them vulnerable to earth's microbes. Further, they feed by injecting human blood directly into their veins, which would be a major infection source if anything (blood transfusion was not well understood back then).