In addition to being potentially fatal, measles symptoms include rashes, blindness and inflammation of the brain. The virus can be transmitted extremely easily, by coughing and sneezing, and it can also survive for hours in a droplet of water.

Measles knows no “geographical or political borders”, O’Brien said, noting nonetheless that since the year 2000, deaths from measles have fallen by over 80% “probably saving around 21 million lives” in that period.

The WHO alert follows its announcement that as of mid-January this year, it had seen 229,068 reported cases of measles during 2018 in 183 Member States, which have until April to file data on the previous year’s disease burden.

This is almost double the 115,117 cases reported at the same point last year, and WHO’s concern is based on the fact that the final number of infections rose to 173,330.

“Due to reporting delays and outbreaks late in 2018, we expect that these numbers will increase, as they have done in previous years,” the agency said in a statement.

In 2018, Africa saw 33,879 measles infections; of these, 4,391 were from Madagascar alone, where 922 deaths have been reported in an ongoing outbreak that began last October. The Americas recorded nearly 17,000 cases of measles in 2018, with the Eastern Mediterranean, just under 22,000.

In Europe, there were 82,596 infections in 47 of 53 countries, ahead of South-East Asia (73,133) and the Western Pacific (23,607), the WHO said. To prevent outbreaks and eliminate measles, the WHO urges countries to sustain high immunisation coverage with two doses of measles vaccine, a regimen which has been administered to “billions” of children, O’Brien told journalists in Geneva.

“We’re backsliding on the progress that has been made, not because we don’t have the tools, but because we’re not vaccinating,” she said. O’Brien further said that there was no association between autism and the measles jab; asserting that the myth has been debunked as the study that started the falsehood was based on erroneous data.

In recent years, vaccine coverage has stalled at 85pc. This is far short of the 95pc needed to prevent outbreaks and leaves many people susceptible to the disease. Second-dose coverage stands at 67pc. Countries should also identify and address all communities that are under-immunised, said Katrina Kretsinger, Medical Officer in the Expanded Programme on Immunization at WHO.

“Some populations are more at risk than others. Children, migrants, refugees and poor populations,” she said. Although the WHO is working in affected regions with ministries of health it won’t commit to a compulsory vaccination recommendation.

“It’s up to the countries to implement vaccination programmes. Some have made it mandatory for children to be vaccinated in order to attend school,” Kretsinger suggested.