RESUMO
ObjectiveSerum antibody levels have been linked to immune protection in SARS-CoV-2 infection. After exposure to the virus and/or vaccination there is an increase in serum antibody titers followed by progressive non-linear waning of antibody levels. Our aim was to find out if this waning of antibody titers would adjust to a mathematical model. MethodsWe studied serum anti-RBD (receptor binding domain) IgG antibody titers over a ten-month period in a cohort of 54 health-care workers who were either never infected with SARS-CoV-2 (naive, nHCWs group, n = 27) or previously infected (experienced, eHCWs group, n = 27) with the virus after the second dose of the BNT162b2 mRNA vaccine. We have selected a risk threshold of 1000 UA/ml anti-RBD Ab titer for symptomatic infection based on the upper titer threshold for those volunteers who suffered infection prior to the omicron outbreak. Two mathematical models, exponential and potential, were used to quantify antibody waning kinetics and the relative quality of the goodness of fit to the data between both models was compared using the Akaike Information Criterion. ResultsWe found that the waning of anti-RBD IgG antibody levels adjusted significantly to both exponential and potential models in all participants from both the naive and experienced groups. Moreover, the waning slopes were significantly more pronounced for the naive when compared to the experienced health-care workers. In the nHCWs group, titers would descend below this 1000-units threshold at a median of 210.6 days (IQ range: 74,2). However, for the eHCWs group, the risk threshold would be reached at 440.0 days (IQ range: 135,2) post-vaccination. ConclusionsThe goodness of the fit of the anti-RBD IgG antibody waning would allow us to predict when the antibody titers would fall below an established threshold in both naive and previously infected subjects.
RESUMO
BackgroundVaccines against SARS-CoV-2 have provided an invaluable resource in the fight against this infection. Given the current vaccine shortage, vaccination programs must prioritize their distribution to the most appropriate segments of the population. MethodsWe carried out a prospective cohort study with 63 health care workers (HCWs) from a public General Hospital. We compared antibody responses to two doses of BNT162b2 mRNA Covid-19 vaccine between HCWs with laboratory-confirmed SARS-CoV-2 infection before vaccination (experienced HCWs) and HCWs who were not previously infected (naive HCWs). ResultsSeven days after the first vaccine dose HCWs with previous infection experienced a 126 fold increase in antibody levels (GMC 26955 AU; 95% CI 18785-35125). However, in the HCW naive group the response was much lower and only 5 of them showed positive antibody levels (>50 AU). The HCWs with previous infection did not significantly increased their antibody levels after the second dose while there was a significant increase in the naive HCW group (16 fold; GMC 20227 AU; 95% CI: 15179-25275). Approximately two months after completing vaccination, the level of antibodies was much lower in naive HCWs (GMC 6595 AU vs. 25003 AU; p<0.001) ConclusionThe study shows that 10 months after the disease has passed, the immune system is capable of producing a rapid and powerful secondary antibody response after one single dose of the vaccine. This response reflects the persistence of immunological memory and it is independent of whether or not anti-SARS-CoV-2 antibodies are detected in blood. Besides, we found that the second dose does not improve the antibody response in individuals with previous Covid-19 infection. Nonetheless, two months later, the persistence of antibody levels is still higher in the experienced HCWs. These data suggest that immune memory remains for a long time in recovered individuals, and therefore, vaccination in this group could be postponed until immunization of the rest of the population is complete.
