In a Facebook post yesterday (Dec 14), Dr Yong said a second booster shot should be saved for when it is absolutely necessary, reports the Bangkok Post.
It should be rolled out after new knowledge has been gained about emerging variants of the virus, or when a new generation of vaccines are produced, said Dr Yong, also chief of the Centre of Excellence in Clinical Virology at Chulalongkorn University.
His remarks came after Prime Minister Prayut Chan-o-cha instructed agencies to plan a fourth vaccine shot for next year as manufacturers will come up with new vaccine production technologies to fight the ever-mutating virus.
Dr Yong said inoculation should not be rushed to reduce risks. The focus should now be on getting double doses to as many people as possible, and offering those who are double-jabbed a booster shot.
Giving a booster jab of either AstraZeneca or an mRNA vaccine should deliver sufficient immune protection to a reasonable degree. More research is being done to assess vaccine efficacy and the drop in immunity among vaccinated people, according to Dr Yong.
He said immunity would be spurred if the third and fourth shots were administered further apart rather than too close together.
Dr Yong said having too many jabs increases the risk of negative side effects.
He suggested people who paid for vaccines and booked appointments for a fourth shot should wait for now. They should receive the second booster at least six months after the first booster.
Meanwhile, government spokesman Thanakorn Wangboonkongchana has outlined a rollout plan for these supplementary jabs.
Recipients of double doses of AstraZeneca should wait three to six months before taking a booster jab of either Pfizer or Moderna.
Those administered with either Pfizer or Moderna can obtain a booster of the same mRNA vaccine after six months of receiving their second jab.
People who had either Sinovac or Sinopharm as their first shot and AstraZeneca as their second can seek a booster of either AstraZeneca or an mRNA vaccine.