Upper respiratory tract is the primary target of SARS-CoV-2. Therefore, nasal immune responses act as the first line of defense against SARS-CoV-2 infection.
The concept of heterologous vaccination against SARS-CoV-2 infection has been adopted in Thailand with limited data on the induction of humoral and cellular immunity, particularly the CoronaVac/ChAdOx-1 (CoVac/ChAd) regimen in the elderly.
Inactivated SARS-CoV-2 (CoronaVac®, Sinovac, or SV) and ChAdOx1 nCoV-19 (Vaxzevria®, Oxford-Astra Zeneca, or AZ) vaccines have been administered to the health care workers (HCWs).