Sinovac's COVID-19 vaccine, called CoronaVac, is currently being tested in a Chinese clinical trial to determine whether or not a third shot will help improve immunity against the virus. Participants of the trial get a third shot eight months after their second jab. As of now, we don't know if receiving a third shot is safe. We also don't know if it will improve protection against the virus. Because of this, it is not recommended that people receive a third CoronaVac dose.

Previous clinical trial data from China's CoronaVac showed that the vaccine's efficacy ranged from roughly 50% to 84% against symptomatic COVID-19 infections in several countries. The largest study involved 10.5 million people. It evaluated vaccine recipients in Chile at least 14 days after they received their second dose. The study showed that CoronaVac was 67% effective at preventing symptomatic COVID-19. It was 85% effective at preventing hospitalizations and 80% effective at preventing deaths caused by COVID-19.

Interestingly, Brazilian researchers found that the vaccine has a higher efficacy (62.3%) when the second dose is given 21 or more days after the first injection, rather than 14 days between shots (50.7% efficacy).

Several countries have put in orders for third shots of some vaccines in case the boosters are shown to be beneficial and efficacious in helping increase protection against the virus. Three jabs of Sinovac's CoronaVac vaccine is not recommended by the World Health Organization or national ministries of health, though it is being studied in some countries now.