Advice on booster jabs
Those who received two Sinovac or Sinopharm shots have been advised to get a viral vector or mRNA vaccine booster, while a fourth jab could even be necessary.
The advice came after a Siriraj Hospital Faculty of Medicine study.
For example, the average immunity of volunteers who received two Sinovac jabs for two weeks was 230 binding antibody units per millilitre (BAU/mL), but their immunity dropped to just 33 BAU/mL 12 weeks after two jabs, head researcher Assoc Prof Dr Nasikarn Angkasekwinai noted on Wednesday.
The study was conducted between July and December last year on four groups of volunteers who received AstraZeneca, Sinopharm or Pfizer (full dose or half dose) as a booster shot.
She explained that after receiving a booster shot for two weeks, the immunity of volunteers who received two Sinovac jabs changed as follows:
• Pfizer (full dose): 5,152 BAU/mL
• Pfizer (half dose): 3,981 BAU/mL
• AstraZeneca: 1,358 BAU/mL
• Sinopharm: 155 BAU/mL
Meanwhile, the immunity of volunteers who received two AstraZeneca jabs changed as follows:
• AstraZeneca 246 BAU/mL
• Sinopharm129 BAU/mL
• Pfizer (full dose) 2,377 BAU/mL
• Pfizer (half dose) 1,962 BAU/mL
Nasikarn said a fourth Covid-19 vaccine jab would be necessary, especially for people who have received two Sinovac shots and an AstraZeneca jab, as the volunteers’ immunity dropped 5-10 times 4-5 months after receiving a booster.
Siriraj Institute of Clinical Research deputy director Suwimon Niyomnaitham concluded that an inactivated vaccine booster jab does not provide immunity, while three viral vector jabs give low immunity.
Suwimon said half a dose of Pfizer gave high immunity, similar to a full dose.
“Hence, we advise people who have received two Sinovac or Sinopharm jabs to receive a viral vector or mRNA vaccine as a booster shot,” she said.
“Those who have received two AstraZeneca jabs should receive an mRNA booster jab to deal with the virus mutation,” Suwimon advised.