BANGKOK (REUTERS) - Thailand is modifying its coronavirus immunisation strategy to target worst-hit areas and sectors where clusters are most likely to emerge, officials said on Wednesday (May 26), as it deals with its most severe Covid-19 outbreak yet and a low vaccination rate.

The strategy prioritises the epicentre Bangkok and nearby provinces, tourism hot spots, construction camps and potential spreaders, like public transport workers, the government's Covid-19 task force said.

Thailand reported a daily record 41 deaths on Wednesday, bringing overall fatalities to 873, about 90 per cent of which were during the current outbreak that started early last month.

The outbreak is also responsible for the bulk of its total 137,894 cases.

Thailand is due to start mass vaccinations next month. Of its more than 66 million people, only 2.5 million have received at least one dose of a coronavirus vaccine so far, mostly the Sinovac brand.

Thailand has reserved 61 million locally made AstraZeneca vaccines for its main drive.

Vaccine distribution had earlier been based on reservations made by the provincial health authorities, some with low cases numbers, said task force spokesman Taweesin Wisanuyothin.

The Health Ministry said two doses of the Sinovac vaccine had reduced the risk of infection by 83.3 per cent, according to its study on the holiday island of Phuket, where 22 per cent of the population has received both required doses.