Fuelled by the anti-vaxxer movement, it's estimated that more than 20 million children a year worldwide over the past eight years have gone without vaccines.
The disease is said to be most risky for children under 5 years of age, adults over 20 years of age, pregnant women, and people with weakened immune systems.
Next came France and Britain, with more than 600,000 and 500,000 unvaccinated children, respectively, during the same period. Of the top 20 countries with the largest number of unvaccinated children in 2017, 9 have not introduced the second dose.
He reiterated: "Vaccination is safe, it's very, very important for the public health - for everybody's health - and we're going to tackle it".
Simon Stevens, chief executive of NHS England, said: "Getting yourself and your children vaccinated against killer diseases is essential to staying healthy, and vaccine rejection is a serious and growing public health timebomb".
The number of cases of measles in England has nearly quadrupled in the past year, leading the head of the health service to issue a warning about the growing number of parents refusing to vaccinate their children.
Faced with new legislation to compel it and other social media firms to fight fake news, Facebook last month vowed to block anti-vax adverts to stop the spread of medical misinformation. Two doses of measles vaccine are over 97 percent protective against the disease.
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Yet due to poor infrastructure, conflict and "mistrust and complacency", global measles vaccine coverage has plummeted, UNICEF says, driving up the number of cases.
Children need two doses of the vaccine for protection, with the World Health Organisation (WHO) recommending 95% coverage to achieve herd immunity, which offers protection against the disease spreading in the community.
The situation is much worse in poor countries like Nigeria, which has the lowest vaccination.
The U.S., which is contending with its biggest measles outbreak in 25 years, had the highest number of children who missed out on the initial dose of the vaccine among high-income countries, a shortfall of more than 2.5 million. It was followed by India (2.9m), Pakistan and Indonesia (1.2m each), and Ethiopia (1.1m).
In 2017, some 110,000 people, a lot of them children, died from measles - a 22 percent increase from the year before, UNICEF said. Last summer, the department investigated three cases of measles in unvaccinated adults.
"We need to work together to improve immunization delivery so that all children are protected from preventable diseases".
The number of measles cases in England more than trebled to 966 previous year.