At least 922 children and young adults have died of measles in Madagascar since October, despite a huge emergency vaccination program, the World Health Organization (WHO) said on Thursday.

The number of deaths is based on official numbers, but these are likely to be very incomplete, as is the current total of infections, at 66,000, Dr Katrina Kretsinger of WHO’s expanded program on immunization told a news briefing.

Measles is a highly contagious viral disease that can cause complications including blindness and brain swelling and increase susceptibility to other diseases.

Madagascar locust crisis Show all 12 1 /12 Madagascar locust crisis Madagascar locust crisis Madagascar locust crisis A swarm of locusts flies over Amparihibe village and threatens its fields. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A farmer protects his rice field from locusts by chasing away them with reeds at Amparihibe village in Tsiroanomandidy, western Madagascar. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A helicopter of the Food and Agriculture Organization of the United Nations (FAO) flies through millions of Locusts as spreads pesticide to fight against a swarm of locusts threatening to reach Amparihibe village. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A farmer from Amparihibe village shows a bag full of locust which will be used to feed pigs, in Tsiroanomandidy, western Madagascar. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A farmer protects his rice field from locusts by chasing away them with reeds at Amparihibe village. A Food and Agriculture Organization of the United Nations (FAO) mission is to fight the locust's swarm with an insecticide. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A man from Amparihibe village walks through a swarm of locusts. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A family from Amparihibe village walks through a swarm of locusts . RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis Members of the technical team of the Food and Agriculture Organization of the United Nations (FAO), prepare insecticide for a helicopter equipped for pesticide spreading in Tsiroanomandidy. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis Members of the technical team of the Food and Agriculture Organization of the United Nations (FAO), wearing masks and gloves, are pictured as they prepare insecticide for a helicopter equipped for pesticide spreading in Tsiroanomandidy. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A swarm of the Red Locusts 20 kilometres north of the town of Sakaraha, south west Madagascar BILAL TARABEY/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis A member of the technical team of the Food and Agriculture Organization of the United Nations (FAO), holds a locust at a FAO camp on May 7, 2014 in Tsiroanomandidy, Madagascar. RIJASOLO/AFP/Getty Images Madagascar locust crisis Madagascar locust crisis Dead locusts are diplayed on a table at a camp of the Food and Agriculture Organization of the United Nations RIJASOLO/AFP/Getty Images

The Indian Ocean island is among Africa’s poorest countries, and in 2017 only 58 per cent of the population had been vaccinated against measles. The lack of a big outbreak since 2003 also means many have had no chance to develop immunity.

An emergency response has vaccinated 2.2 million of the 26 million population so far, Dr Kretsinger said. Some of those had previously been vaccinated but had only received one shot, and so were given the more standard second, “booster” jab.

“We believe that should go a long way toward stemming the current outbreak,” she added.

Madagascar has Africa’s highest children’s malnutrition rate, at 47 per cent. The condition can increase the risk of serious complications and death from measles infection, the WHO says.

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The disease can also leave children vulnerable to potentially fatal pneumonia or diarrhoeal diseases months later, said Katherine O’Brien, WHO director of Immunization, Vaccines and Biologicals.

Madagascar plans to standardise on a routine two-dose vaccination program later this year.