On January 2nd, 2022, Professor Thailand | Daily News”>Yong Phuworawan, the director of Chulalongkorn University‘s Faculty of Medicine’s Department of Pediatrics’ virology clinic, shared a post on his Facebook page, “Yong Poovorawan,” detailing …
COVID-19 Vaccine: Three-Dose Regimens in Thailand
Yong Phuworawan, January 2, 2022
The three-dose vaccine program uses mRNA and viral vector platforms including Pfizer (PZ), Moderna (MN), and AstraZeneca (AZ).
This update presents data on mRNA booster strategies employed in Thailand. The analysis focuses on two-dose regimens of inactivated vaccines—SP-SP, SV-SV, SV-AZ, and AZ-AZ—widely used in the nation. This clinical trial meticulously documented adverse events. The protocol mandated a 5-7 month interval between the second and third doses. All participants were over 18 and in good health. A limitation was the AZ-AZ group’s older age demographic, reflecting the Thai population. Blood samples were collected pre-injection, at two and four weeks post-second dose, with a follow-up planned at 90 days post-third dose.
In Thailand, mRNA vaccines primarily serve as booster shots due to the widespread prior administration of other vaccines. Findings on the SV-SV-AZ group’s effectiveness have been published, while data on the SV-AZ-AZ and AZ-AZ-AZ regimens are forthcoming, as these are presently undergoing volunteer trials.
In the United States, Moderna is used as a booster, often at a half dose after Pfizer, Moderna, or J&J viral vector vaccines.
Similarly, the United Kingdom utilizes a reduced-dose Moderna booster followed by AZ to mitigate adverse reactions. Common side effects include injection site pain, arm mobility limitations, myalgia, headache, nausea, diarrhea, and notably, axillary lymphadenopathy, more pronounced after the third dose than after the first two (per US CDC data). Consequently, half-dose studies were also conducted. Initial findings encompass two immunological indicators: total immunoglobulin per RBD (unit/ml) and specific IgG per RBD of the spike protein (BAU/ml).
Research by the Chulalongkorn University Clinical Virology Center demonstrates the efficacy of booster shots. The data, illustrated graphically, shows the immune response after two doses of inactivated vaccines (SV-SV, SP-SP, SV-AZ, AZ-AZ).
The booster shots induced robust immune responses. Both assays showed consistent results: prior SV-SV vaccination resulted in the strongest immune response exceeding those from SP-SP, SV-AZ, and equaling that from AZ-AZ.
Nevertheless, all groups exhibited high immunity levels.
Currently, a three-dose Pfizer regimen (triple P) is being evaluated in Thailand for benchmarking (a substantial sample size is now available ). The three-dose AstraZeneca regimen (triple A) is also under investigation to provide a complete overview of all regimens used nationally, while the three-dose Moderna regimen (triple M) remains less prevalent, requiring more
