Many studies have demonstrated that vaccine-induced immunity begins to decline at least six months after the second shot. However, it is unclear if the rate of decline is the same for every person who has been vaccinated.
A new study out of Japan has identified many risk factors for declining immunity post-vaccination.
Understanding who is most susceptible to waning immunity can allow public health officials tailor vaccination schedules for those with the lowest antibody levels. Priority for booster injections, a personalized vaccination schedule, or the use of an adenovirus-based vaccine rather than an mRNA vaccine are all examples of this.
A total of 365 vaccinated healthcare workers from a hospital in Tochigi prefecture were recruited for the study, with 250 women and 115 men. The average age was 44 years old. Nurses and doctors made up 56.2 percent of the participants in the study.
Participants’ antibody titer levels against the SARS-CoV-2 spike protein were assessed six months following vaccination.
The cohort’s median antibody titer was around 539 U/mL.
Smoking and decreased antibody levels
Antibody titer levels were about half of those reported in people in their 20s. Antibody titers declined with age from 20 to 70.
Outside variables such as hypertension may have altered age-related outcomes, thus the researchers modified the data. Reanalysis found only smoking to be associated with reduced antibody titers.
“In terms of smoking, the age-adjusted median Ab titers were −97 (−277 to 184) and 56 (−182 to 342) in ever-smokers and never-smokers, respectively,” said the researchers.
Gender vs. waning immunity
Anti-SARS-CoV-2 antibody titers decreased by 29.4%. Age had no effect on the decline rate, but sex did.
Women lost 6.5 percent more than men.
Women’s median change in antibody titers was 31.6 percent. Men, on the other hand, changed by -25.1 percent.
The team reanalyzed antibody titers at three and six months following vaccination in men and women who smoked versus those who did not.
When it came to smoking, there was no barrier between men and women. However, there were significant gender disparities between smokers and nonsmokers.
Finally, after six months, there was a positive association between antibody titer levels and rate of reduction. The participants with the lowest antibody titer levels showed a faster rate of change in antibody titers after six months. Individual characteristics not taken into account in the study could have also influenced declining immunity, according to the researchers.
Some limitations of the study
The fact that all of the participants came from a single Japanese national hospital raises the question of generalizability for the rest of Japan and the rest of the world.
Since the researchers only intended to look at vaccine-induced immunity, they excluded those who had antibodies to nucleocapsid proteins, assuming that meant they developed immunity after recovering from infection. However, several of the patients who were excluded exhibited no signs of waning spike protein immunity yet tested negative for antibody protection against SARS-CoV-2 nucleocapsid proteins.
It’s possible that 5 of the subjects who had an 80% increase in antibody titers against the spike protein (but not against nucleocapsid proteins) were infected with COVID-19. The 5 participants were not eliminated from the final analysis because there was no clear evidence or verified test of COVID-19.
The study concluded that Old age and smoking were amongst those with some of the lowest antibody titers. Women more than men were also more likely to experience a rapid decline in antibody levels 3 to 6 months after receiving their second Pfizer-BioNTech dose.
Source: 10.1101/2021.11.14.21266334
Image Credit: iStock
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