“`html
On January 2nd, Professor Yong Phuworawan, director of the virology unit at Chulalongkorn University‘s pediatric department, shared insights on COVID-19 vaccination strategies via his Facebook page. His post detailed the efficacy of three-dose booster regimens using various mRNA and viral vector vaccines available in Thailand, including Pfizer (PZ), Moderna (MN), and AstraZeneca (AZ).
The professor presented data from a clinical trial assessing different two-dose primary vaccination combinations (SP-SP, SV-SV, SV-AZ, AZ-AZ) followed by a booster. This research meticulously documented adverse reactions and mandated a 5-7 month interval between the second and third doses. All participants were over 18 and healthy; however, the study noted a higher average age in the AZ-AZ group, reflecting Thailand’s demographics. Blood samples were collected pre-injection and at two and four weeks post-second dose, with a final collection planned for 90 days post-booster.
In Thailand, mRNA vaccines primarily serve as boosters due to the widespread prior use of other vaccine types. Results from the SV-SV-AZ group have been published, with findings from the SV-AZ-AZ and AZ-AZ-AZ groups forthcoming, as these trials are ongoing.
In the United States, Moderna is employed as a booster, often at a half-dose, following Pfizer, Moderna, or Johnson & Johnson vaccination.
The United Kingdom similarly utilizes a reduced Moderna booster dose after AZ administration to mitigate adverse events. Common side effects across studies include injection site pain, arm weakness, generalized aches, headache, nausea, diarrhea, and notably, axillary lymphadenopathy, more pronounced after the booster than earlier doses (per US CDC data).
Consequently, half-dose studies were conducted. Initial results show two key immune response metrics: total immunoglobulin per RBD (unit/ml) and specific IgG per RBD of spike protein (BAU/ml).
Research from Chulalongkorn’s virology center demonstrates the booster dose’s impact on immunity following various primary vaccine regimens (SV-SV, SP-SP, SV-AZ, and AZ-AZ).
The booster significantly enhanced immunity in both measured parameters. Those previously vaccinated with SV-SV exhibited the strongest immune response, surpassing SP-SP, SV-AZ, and showing equivalence to AZ-AZ.
Despite variations, all groups displayed substantial immune responses.
Currently, data is being collected on a three-dose Pfizer regimen (triple P), with a similar effort underway for a three-dose AstraZeneca series (triple A) to encompass all prevalent Thai vaccination strategies. Three-dose Moderna (triple M) trials are less common due to limited availability.
Half-dose mRNA boosters, especially Moderna, showed comparable efficacy to full doses, with noticeably fewer side effects, due to already high baseline immunity.
Neutralizing antibody (NT) levels are being assessed using various methods. Studies employing pseudoviruses and live viruses (Delta and Omicron variants, directly isolated from patients) are underway (partially conducted by Professor Jutathip et al at Siriraj and CMIR), with
