The decision comes after hundreds of medical workers caught Covid despite being fully vaccinated with Sinovac.
Instead of two Sinovac shots, people will now receive the AstraZeneca vaccine after their first Sinovac shot.
Health workers already fully vaccinated with Sinovac will also receive a third booster from a different vaccine.
This can be either the AstraZeneca vaccine, or an mRNA vaccine like Pfizer/BioNTech. This third dose will be given three to four weeks after their second Sinovac jab, said the country's National Infectious Disease Committee on Monday.
AstraZeneca is currently the only other vaccine available in the country, with Pfizer/BioNTech shots donated by the US set to arrive soon.
Thailand first received Sinovac vaccines from China and began giving shots to its health workers in February.
According to a study published in the New England Journal of Medicine showing results from Chile, Sinovac has an efficacy rate of 65.9% against Covid-19, is 87.5% effective at preventing hospitalisation and 86.3% effective at preventing death.
Thailand is currently in the midst of a spike of new infections, reporting a record high of 9,418 on Sunday. The death toll for the previous day stood at 91, also a record number.
Concerns over the efficacy of the Chinese vaccine amid rising cases have sharply driven demand for other shots offered by some private clinics.
Last week, one clinic selling the US Moderna vaccine on an online shopping platform saw its offer sold out within minutes. The Phyathai Hospital offered 1,800 vaccination slots for a single Moderna shot at 1,650 Thai baht ($50, £36) via Shopee.
Overall, Thailand has seen more than 345,000 confirmed cases of Covid-19 and nearly 2,800 deaths since the beginning of the pandemic in 2020, according to figures collated by Johns Hopkins University from around the world.
There are concerns that the spike in cases in many South East Asian countries is due to the spread of the more infectious Delta variant, first discovered in India.