BOOSTER DOSING 

Booster at 6 months after Dose 2 implemented in several countries. WHO recommends 3rd dose for persons over 60 and 1-3 months after dose 2 in immune compromised but labels as 3rd dose in a primary series. Three doses of mRNA vaccine is the only current effective strategy against the Omicron variant

INTERCHANGEABILITY

WHO allows another kind of vaccine to be used for Dose 3 of Sinovac. CDC recommends that persons aged ≥ 18 years (including moderately or severely immunocompromised persons who received an additional primary dose) who were fully vaccinated with a WHO EUL vaccine not authorized/approved by US FDA or with a heterologous series composed of any FDA-authorized/approved or WHO EUL authorized vaccine are eligible to receive a single booster dose of the Pfizer vaccine (0.3 mL; 30 µg) at least 6 months after completion of their primary series under the existing age guidelines as for Moderna and Pfizer vaccines. Practically, either mRNA vaccine may be used for a booster in this situation.