Antibodies after COVID-19 vaccination peak higher for women and younger people than men and individuals over the age of 65, respectively, but levels drop by half within six months for everyone in a study group.
A new study led by Texas Biomedical Research Institute (Texas Biomed) and the University of Verona in Italy has found that antibody levels after Pfizer-BioNTech COVID-19 vaccine vary by age and sex, but across the board, antibody levels dropped significantly within six months.
Individuals under the age of 65 had more than twice the level of antibodies than individuals 65 years and older throughout the six months following vaccination. Also, women had higher antibody levels than men and levels decreased by more than 50% from peak levels for everyone in the study.
“While we see how well vaccines have helped keep people out of the hospital and prevent life-threatening disease, antibody levels are quickly declining in all persons regardless of age and sex,” says Brandon Michael Henry, MD, a physician scientist and postdoctoral researcher at Texas Biomed who co-led the study with collaborators in Italy. “Our study provides additional evidence that booster shots for all adults will be important to keep antibody levels up so we can continue to mount an effective immune response against COVID-19 infection and prevent COVID-19 fatalities.”
The study included 787 healthcare workers in Verona, Italy who received two doses of the Pfizer-BioNTech COVID-19 vaccine. They ranged in age from 21 to 75. Their antibody levels were measured before vaccination, after the second dose, and at one, three and six months after the second shot.
The researchers theorize that the differences in sex have to do with hormones. Testosterone, which is higher in men, naturally suppresses the immune system and on the other hand estrogen, higher in women is known to amplify immune responses.
“We have observed throughout the pandemic more older people and men suffer the worst consequences of COVID-19,” Dr. Brandon Michael Henry says. “These studies point to weaker immune responses against SARS-CoV-2 as a contributing factor to this phenomenon.”
The researchers pointed out that the fact that antibody levels are declining does not mean that the vaccines are not effective. The antibodies that help prevent severe disease appear to continue to be effective in most groups even if present at a lower level, which is why vaccination is important. However, as these antibodies will continue to decline with time, booster doses can help maintain adequate levels of these lifesaving antibodies.