A laboratory study revealed that the antibodies produced by the Sinovac Biotech COVID-19 vaccine declined to below a significant level for prevention approximately six months after the second dose in most individuals. However, receiving a third dose had a strong boosting effect. Chinese researchers announced these findings based on blood samples from healthy adults aged 18 to 59 in research published on Sunday, although comparative studies have yet to be conducted.
The researchers noted that it remains unclear how the decline in antibodies will affect vaccine efficacy, as scientists have not precisely determined the minimum antibody levels produced by any vaccine that are sufficient for disease prevention.
**Hope in the Third Dose**
The study also disclosed that vaccine recipients in certain groups who received a third dose of Sinovac approximately six months after the second dose experienced an increase in antibodies by about three to five times compared to their levels 28 days after the third dose, when compared to the levels recorded four weeks after the second dose.
However, researchers cautioned that the study did not test the efficacy of antibodies against more transmissible strains of the coronavirus, adding that further research is needed to measure the duration of antibody effectiveness following a third dose.
