Not comparing like with like

From the BBC:

Every year they stop an estimated two to three million deaths, preventing more than 20 life-threatening diseases, according to the World Health Organization (WHO).

Childhood illnesses that were common less than a generation ago are increasingly rare. And smallpox - which killed hundreds of millions of people - has been completely eradicated.

But these successes have taken decades to achieve - and many of us are now expecting effective coronavirus vaccines to have similar results in a radically shorter time frame.

Of course it took decades, because vaccinations against diptheria, whooping cough and measles were just given to young children on reaching a certain age, and it took a few decades before mass immunity against each of these was achieved.

If the UK government and/or NHS get things sorted out and manages to vaccinate [nearly] the whole population within a year, then surely we'll achieve in a year what used to take decades?