The latest outbreak has accounted for more than half of Thailand's total infections and deaths and slowed domestic activity.
The consumer index of the University of the Thai Chamber of Commerce fell to 46.0 in April from 48.5 in March.
"Consumers felt the economy had not recovered much and lacked catalysts despite government measures boosting some spending," university president Thanavath Phonvichai told a briefing.
Consumer confidence will remain on a downward trend with no signs of recovery until new infections decrease and more vaccinations are administered, he said.
The university estimates an economic loss of between 400 billion baht to 600 billion baht if the spread continues beyond this month, Thanavath said.
The government should scramble to implement fresh relief measures to help shore up the economy, he added.
On Wednesday, the government approved a relief package worth 255 billion baht to mitigate the impact of the outbreak. - Reuters