The WHO’s stand on 3rd dose
For Sinopharm, the WHO interim recommendation (first issued on May 7, 2021 and updated on October 28, 2021) states: “Emerging evidence suggests that older persons and immune-compromised individuals mount a lower immune response after a standard primary series (two-dose schedule) compared to younger individuals and those without immune-compromising conditions. “Therefore, for older adults and immune-compromised persons who have received a standard two-dose primary series of Sinopharm, the WHO recommends an additional dose. “For the additional (3rd) dose in an extended primary series, WHO recommends an interval of three to six months between the 2nd and 3rd doses. If more than 6 months have elapsed since the second dose, the third dose should be administered as soon as possible.” Meanwhile, the United States of America, Canada, the United Kingdom, Australia and Singapore all recommend a ‘booster’ dose for those who received the AstraZeneca or an mRNA vaccine (Pfizer/Moderna) six months, at least, after the 2nd dose.