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TO THE EDITOR—In reply to the correspondence from Tjan et al [1] regarding the heterologous booster in healthy adults previously immunized with 2 doses of CoronaVac [2], the additional knowledge on immunogenicity of the booster (third dose) with BNT162b2 in BNT162b2-primed individuals against the BA. 2 omicron variant will help promote the vaccine uptake and coverage in the midst of a surge in BA. 2 omicron worldwide.

As of February 2022, the omicron variant was further classified into 4 main sublineages, BA. 1, BA. 1.1, BA. 2, and BA. 3. Moreover, an epidemiological surveillance on coronavirus disease 2019 (COVID-19) showed that BA. 2 sublineages have become the dominant variant globally [3]. In Thailand, the BA. 2 sublineages have been detected since the end of January 2022. The proportion of BA. 2 sublineages rapidly increased and accounted for more than 90% of positive cases reported in …