The Public Health Ministry has defended four senior doctors who were strongly criticised on social media for their alleged involvement in the selection of vaccines.

The ministry on Tuesday issued a statement saying the four doctors have worked tirelessly to fight Covid-19 and were never involved in ministry decisions to buy Covid-19 vaccines.

"These medical advisers only gave advice to the ministry on fighting the spread of Covid-19. They should be respected by the public. They have greatly contributed to helping the ministry [control the outbreak]," said Kiattiphum Wongrajit, permanent secretary at the Public Health Ministry.

Dr Kiattiphum said the four doctors are Yong Poovorawan, chief of the Centre of Excellence in Clinical Virology at Chulalongkorn University; Tawee Chotpitayasunondh, an expert on the national committee on communicable disease; Prasit Watanapa, dean of the Faculty of Medicine Siriraj Hospital; and Kulkanya Chokephaibulkit, director of the Siriraj Institute of Clinical Research.

Dr Kiattiphum said he felt uneasy when he heard some people had harshly criticised these doctors. He said it was necessary for the ministry to issue a statement to protect their reputations.

"They are also medical academics who can express any comments or suggestions freely. They have never been involved with the ministry's buying of [Covid-19] vaccines or any other medical tools. Furthermore, we appreciate their dedication in helping the country," he said.

Those criticising the four physicians believed the doctors were behind the ministry's decision to bring in a large quantity of Sinovac, which has been said to have low efficacy against the Delta variant.