Four months ago 10-year-old Hassan Merzam Muhammad was so severely malnourished he was unable to walk or react, carried limp into a Yemeni clinic by his father.

Then, his image in one of Reuters pictures of the year helped draw world attention to his country's plight. Today, after treatment, he plays with a toy car, sits on a donkey and - mute since birth - uses hand signals and a smile to communicate.

But malnutrition hangs like a spectre over him and 2 million other Yemeni children as war, economic decline and COVID-19 push Yemen closer to what the United Nations warns could be the worst famine for decades.

"Hassan eats what we eat: rice, bread. We don't have fat-rich foods nowadays, we cannot find meat for him," his uncle Tayeb Muhammed said.

Hassan has lost some of the weight gained during treatment since returning to his family's hut. Displaced five times by war, they now live in rural Hajjah, one of the poorest regions. His father has no work to provide for his seven children.

When Reuters first met Hassan in July he weighed just 9 kilos. A struggling local health clinic sent him to the capital Sanaa for treatment, paid for by a charity. He now weighs just over 13 kilos.

"His body is weak again," his uncle told Reuters, and he needs more treatment.

Famine has never been officially declared in Yemen, where the more than five-year-old war has left 80% of the population reliant on aid in what the U.N. says is the world's largest humanitarian crisis.

U.N. warnings in late 2018 of impending famine prompted an aid ramp-up. But this year coronavirus restrictions, reduced remittances, locusts, floods and significant underfunding of the 2020 aid response are exacerbating hunger.

Doctor Ali Yahya Hajer, at Hassan's local clinic, said the family needs nutritional baskets delivered to their home until the child's and the family's situation stabilises.

The war in Yemen, in which a Saudi-led coalition has been battling the Iran-aligned Houthi movement since 2015, has killed more than 100,000 people and left the country divided with the Houthis holding Sanaa and most major urban centres.

Reuters