A project giving health workers cheap smartphones to track their progress through rural Pakistan has seen vaccination rates soar.

The scheme carried out with British help cost less than £1m and has led to hundreds of thousands more children immunised. It is now being copied across the world.

Location data from the phones was used to help planners understand why workers were failing to hit vaccination targets in Punjab province.

The data revealed for the first time where villages were being missed or ignored because of a shortage of staff, because health teams had been bunking off, or because the government was not paying transport allowances.

Handing out the £60 phones ($80) saw the vaccination campaign quickly reach nearly every village and immunisation rates climb from 47 per cent to 82 per cent over two years.