Jakarta, July 28 : Four million medical workers will receive a fourth dose of the Covid-19 vaccine amid increasing transmissions triggered by the virus' sub-variants in Indonesia, Health Minister Budi Gunadi Sadikin said. Sadikin told local media on Wednesday that administering of the third dose of the Covid-19 vaccine started in August 2021 and now it is the time for a new immunity shot, Xinhua news agency reported. "So they need a fourth dose to re-strengthen their immune system. We prioritise medical workers," he added. The available vaccine stock is sufficient for the use for all medical workers, Sadikin said. The Southeast Asian country has seen a resurgence in cases recently, triggered by the spread of the Omicron sub-variants BA.4 and BA.5. Authorities also have detected some cases with the BA.2.75 sub-variant which the World Health Organisation has categorised as a Variant of Concern Lineage Under Monitoring. /IANS