The more symptoms the better? Covid-19 vaccine side effects and long-term neutralizing antibody response.

Protection against SARS-CoV-2 wanes over time, and booster uptake has been low. This study explores the link between post-vaccination symptoms, biometric changes, and neutralizing antibodies (nAB) after mRNA vaccination. Data were collected from adults (n = 363) who received two doses of either BNT162b2 or mRNA-1273, with serum nAB concentration measured at 1 and 6 months post-vaccination. Daily symptom surveys were completed for six days starting on the day of each dose. Concurrently, objective biometric measurements, including skin temperature, heart rate, heart rate variability, and respiratory rate, were collected. We found that certain symptoms (chills, tiredness, feeling unwell, and headache) after the second dose were associated with increases in nAB at 1 and 6 months post-vaccination, to roughly 140-160% the level of individuals without each symptom. Each additional symptom predicted a 1.1-fold nAB increase. Greater changes in skin temperature and heart rate after the second dose predicted higher nAB levels. Skin temperature had a stronger predictive relationship for 6-month than 1-month nAB level. In the context of low ongoing vaccine uptake, our findings suggest that public health messaging could seek to reframe systemic symptoms after vaccination as desirable.