The Public Health Ministry has approved additional booster jabs against Covid-19 every four months for those who have already received three doses.
Dr Opas Karnkawinpong, director-general of the ministry's Department of Disease Control (DDC), said the DDC's sub-committee on promoting disease immunity cited data indicating that immunity declines three to four months after vaccination.
Dr Opas said high-risk groups -- people aged 60 and older, those with underlying conditions and pregnant women -- can get boosters every four months as necessary. Those with plans to travel abroad, or with compromised immunity, are advised to do the same.
A study by Dr Kulkanya Choke- phaibulkit, director of the Siriraj Institute of Clinical Research, and Dr Yong Poovorawan, head of the Centre of Excellence in Clinical Virology at Chulalongkorn University, confirmed that a first dose of Sinovac followed by a Pfizer shot can boost immunity for children aged five to 11.
"The sub-committee's decision approves a low-dose Moderna shot or 25 micrograms per dose for children aged six to 11 years. The gap between each shot should be four to 12 weeks," said Dr Opas.
The sub-committee said people who get a Covid-19 vaccine can be inoculated with other vaccines the same day. However this excludes viral vector vaccines, which require a one-month gap as they use live viruses to carry DNA into human cells, and simultaneous injection would lower efficiency.