A study by a team of medical researchers in Japan found that the antibody level boosted after the second dose of Pfizer/BioNTech’s mRNA vaccine starts declining in 3 to 6 months and the most important factors associated with this lowering rate are age and smoking.  The study also found that antibody titers seemed to be going down significantly after 3 months of the second dose in women, showing the sex difference greatly influences the drop in antibody level provided by BNT162b2 coronavirus disease 2019 (COVID-19) mRNA vaccine.   

The study enrolled 365 healthcare workers (250 women, 115 men). The 3-month antibody titres of these people were analyzed after collecting blood samples (183 ±) 15 days after the second dose. Participant characteristics, which were collected previously, were used. The relationships of these important factors with antibody levels at 6 months and rates of change in antibody titres during 3-6 months were also analysed. In these analyses, it was found that older participants had significantly lower antibody titres (20s, 752 U/mL; 60s–70s, 365 U/mL). In age-adjusted analysis, smoking was the only factor associated with lower antibody titres. Median rate of change in antibody levels during 3-6 months was −29.4%. However, the only factor very significantly associated with the rate of change in antibody level within the shorter period of 90 to 180 days was not age or smoking, but sex — women: 31.6 percent lower and men: 25.1 percent lower– the study found. 

The new findings will not only help decide the need of a booster dose but also determine the vaccine dosage for all considering these influencing factors.