EC19V Reply to Lianhe Zaobao Forum Letter on 3-Dose Regime for Sinovac-CoronaVac

Three-dose regime for Sinovac-CoronaVac was recommended based on World Health Organization’s guidance and clinical studies

In her letter dated 25 Oct, Ms Li Ning asked for the reason for having a the three-dose regime for Sinovac-CoronaVac vaccine. She thinks this is not in line with WHO’s guidance or international practice.

The World Health Organization's (WHO) Strategic Advisory Group of Experts on Immunisation (SAGE) provided guidance on 21 October 2021, that a third dose of Sinovac-CoronaVac should be administered between three to six months after the second dose. Priority should go to older adults and immunocompromised persons, and the third dose may be required for populations where the immune response following the standard primary series is deemed likely to be insufficient. SAGE further noted that if more than six months have elapsed since the second dose, the third dose should be administered as soon as possible.

In addition, several countries, including Malaysia, Chile, Brazil and also China have also started to offer a third vaccine dose to persons who have received their first two doses six months ago, including persons aged below 60 years of age.

SAGE’s recommendation was made based on studies that show that antibody levels after vaccination with Sinovac-CoronaVac decline rapidly after three months, and to pre-vaccination levels by six months. This occurs in both younger and older adults.  However, other studies showed that a third dose will raise the antibody levels to multiple folds higher than those observed after the second dose, and will give protection against severe illness and deaths if infected with COVID-19.

Given international evidence, and WHO SAGE’s guidance, the Expert Committee on COVID-19 Vaccination has recommended for a three-dose regime for the Sinovac-CoronaVac vaccine for all age groups.

Benjamin Ong (Associate Professor)

Chairman

Expert Committee on COVID-19 Vaccination