Measles has killed almost 5,000 people in the Democratic Republic of Congo so far this year, authorities have said.
Nearly a quarter of a million people have been infected in the African nation in 2019, with cases in every corner of the country.
The World Health Organisation (WHO) said it was the world's largest and fastest-moving epidemic.
In September the government launched an emergency vaccination programme with the aim of immunising more than 800,000 children.
Measles has killed almost 5,000 people - mostly children - in the Democratic Republic of Congo in 2019 (file image)
But roughly four million children - around half of the total in the country - remain unvaccinated and not enough jabs are available.
The majority of measles deaths in the country have been infants whose immune systems are too weak to fend off the illness.
Poor infrastructure and lack of access to routine healthcare have also stalled efforts to curb the crisis.
The African nation is also currently in the grips of an Ebola crisis, which has killed more than 2,100 people.
Earlier this year Britain lost its measles-free status three years after the virus was eliminated in the country.
The number of Britons vaccinating themselves or their children against the virus has steadily declined in recent years, while cases of measles have quadrupled in the last 12 months. In the first quarter of this year, there were 231 confirmed cases.
It comes as the DRC battles the second largest Ebola outbreak in history, which has killed more than 2,100 people
Britain was declared ‘measles free’ by the World Health Organisation in 2016 after a 36-month period with no ‘endemic’ transmission.
This meant the only outbreaks in that time had started abroad and were then passed on.
Since 2016, however, uptake of the MMR (measles, mumps, and rubella) jab has fallen each year and the WHO has revoked the country’s measles-free status.
Politicians are alarmed about ‘creeping cynicism’ surrounding the safety of vaccinations partly driven by the antivaxx movement, which spreads scare stories, conspiracy theories and false information about the jabs online.
Measles is a highly contagious viral infection that spreads easily from an infected person by coughing, sneezing or even just breathing.
Symptoms develop between six and 19 days after infection, and include a runny nose, cough, sore eyes, a fever and a rash.
The rash appears as red and blotchy marks on the hairline that travel down over several days, turning brown and eventually fading.
Some children complain of disliking bright lights or develop white spots with red backgrounds on their tongue.
In one in 15 cases, measles can cause life-threatening complications including pneumonia, convulsions and encephalitis.
WHAT IS MEASLES, WHAT ARE THE SYMPTOMS AND HOW CAN YOU CATCH IT?
Measles is a highly contagious viral infection that spreads easily from an infected person by coughing, sneezing or even just breathing.
Symptoms develop between six and 19 days after infection, and include a runny nose, cough, sore eyes, a fever and a rash.
The rash appears as red and blotchy marks on the hairline that travel down over several days, turning brown and eventually fading.
Some children complain of disliking bright lights or develop white spots with red backgrounds on their tongue.
In one in 15 cases, measles can cause life-threatening complications including pneumonia, convulsions and encephalitis.
Dr Ava Easton, chief executive of the Encephalitis Society told MailOnline: 'Measles can be very serious.
'[It] can cause encephalitis which is inflammation of the brain.
'Encephalitis can result in death or disability.'
Treatment focuses on staying hydrated, resting and taking painkillers, if necessary.
Measles can be prevented by receiving two vaccinations, the first at 13 months old and the second at three years and four months to five years old.
Source: Great Ormond Street Hospital