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.
COVID-19 Vaccines, which include mRNA and inactivated vaccines, have been proven effective and safe for infants and children aged more than six months in reducing the severity of the disease, hospitalization, multisystem inflammatory syndrome in children, and death.
A novel severe acute respiratory syndrome COVID-19 caused by coronavirus SARS-CoV-2 has been confirmed to infect more than 100 million people globally, with mortality reaching nearly 3 million as of March 2021.
Two main strategies to cope with the coronavirus disease 2019 (COVID-19) pandemic—lockdown (social restriction) and non-lockdown (herd immunity plan)—have been implemented in several countries.