Donald Trump may be the most dangerous President in US history, but not for the reason people fear most. Putting to one side questions about his dealings with Russia, support for Nuclear proliferation, illegal Muslim travel ban, and desire to wall-off Mexico – not to mention his views about women – Trump is an avowed ‘anti-vaxxer’, taking to Twitter in 2014 to support the discredited claim that the MMR vaccine causes autism, and then repeating his error in a September 2015 Republican primary debate stating:

“You take this little beautiful baby, and you pump – I mean, it just looks like it is meant for a horse, not for a child, and we had so many instances, people that work for me, just the other day, 2 years old, beautiful child went to have the vaccine and a week later got a tremendous fever, got very, very sick, now is autistic.”

And it seems that it’s not only the MMR vaccine that he has in his sights. In January Trump invited well-known vaccine-sceptic Robert F Kennedy Jr to Trump Tower to discuss, according to Kennedy, “vaccine safety and scientific integrity.” Kennedy got one thing right, however, when he added in defence of his meeting, “we ought to be debating the science.”

We certainly should be debating the science, because the science is unequivocal: the widespread introduction of vaccines for a host of diseases was the greatest lifesaver of the Twentieth Century, not only sparing millions of families the pain of death and disability, but also transforming parts of the world through trade and economic development. In 1979 the world celebrated the success of the global campaign to eradicate smallpox, an achievement only made possible by the development of the smallpox vaccine by Gloucestershire doctor Edward Jenner nearly two hundred years earlier.

To this day smallpox remains the only disease to be eradicated but, as my book The Health of Nations explores, the eradication of a second disease, polio, is now tantalisingly close – an epic achievement brought about by the announcement fifty-two years ago that Dr Jonas Salk had developed the Inactivated Polio Vaccine (IPV) which, followed by the introduction of Albert Sabin’s Oral Polio Vaccine (OPV), led polio cases to plummet around the world. In the US, polio cases fell by 80-90% in the two years following the introduction of the polio vaccine, while no naturally occurring cases of polio have been reported in the UK since 1982.

Eradicating a disease is no easy task and almost all efforts to do so have ended in failure. Global health workers have many things standing in their way; vast inhospitable terrain, outbreaks of war, religious objectors, funding gaps, and changes in government priorities. Yet the strongest weapon in their arsenal remains the vaccines themselves.

To take one example, the development and introduction of MenAfriVac, a vaccine for meningococcal A meningitis, the strain most destructive to communities in Africa’s meningitis belt, has been a stunning success, protecting more than 235 million people in more than 26 countries. Thanks to this one vaccine alone, meningitis A is almost a thing of the past in sub-Saharan Africa.

If worldwide contributions to vaccine efforts stay on course, it is estimated that 23.3 million lives will be saved due to immunization between 2011 and 2020. Privately, of course, health workers fear that under the Trump administration such efforts will not stay on course, and that the rise of ‘alternative facts’ puts global health programs including those for polio, malaria and measles, in peril.

Research shows that one third of Trump’s supporters agree with his anti-vaccination rhetoric. But vaccine scepticism is a much wider phenomena, with fears of the “poisoned lancet” stretching back for centuries only to be made popular again in middle-class Britain and America by growing support for ‘alternative medicine’ and organic living. If vaccine-refusal rates continue to grow, inaccurate vaccine scepticism will be responsible for turning the clock back to an era when families were blighted by illnesses like polio, measles and whooping cough. (The year that the polio vaccine was announced was also the year of the Montgomery bus boycott, the opening of Disneyland and the hanging of Ruth Ellis). In the intervening decades we have been more than happy to see the back of these childhood killers, but we should be in no doubt that by giving casual credence to the claims of vaccine sceptics, we are putting millions of lives at risk.