COVID-19 antibodies in convalescent plasma donations wane by 3 to 4 months
COVID-19 antibodies in convalescent plasma began to disappear in donations made 3 to 4 months after symptom onset, according to results of a longitudinal analysis published in Blood.
Therefore, convalescent plasma as a treatment may be more effective when collected shortly after the donor’s recovery, according to the researchers.
“While many clinical trials are underway to better understand whether convalescent plasma is clinically beneficial for treating COVID-19, questions remain about when it is most effective to collect donor plasma based on the presence of antibodies that help the virus,” Renée Bazin, PhD, director of innovation in the department of medical affairs and innovation at Héma-Québec and adjunct professor in the department of biochemistry and microbiology at Laval University in Canada, said in a press release. “Based on our findings, antibodies against the new coronavirus are not eternal.”
Previous studies have suggested the benefit from using convalescent plasma is correlated with the presence of SARS-CoV-2 neutralizing antibodies.
An ongoing trial in Quebec is evaluating whether transfusion of COVID-19 convalescent plasma is associated with a reduced risk for intubation or death in adults hospitalized for COVID-19.
The trial includes 282 plasma donors who were diagnosed with and recovered from COVID-19 and who donated their convalescent plasma beginning at least 14 days after the resolution of their symptoms.
Researchers evaluated the seropositivity of the plasma donations using a semiquantitative enzyme-linked immunosorbent assay.
The overall proportion of convalescent plasma donors that tested seronegative at the time of donation was 6.9%. However, this increased to 15% when researchers evaluated plasma from donors who waited for more than 11 to 12 weeks after symptom onset before donating, the researchers wrote.
Based on that finding, Bazin and colleagues followed 15 donors (11 men; median age, 56 years; range, 20-67 years) who donated their plasma between four and nine times, with the first donation occurring 33 to 77 days after symptom onset and the last donation occurring 66 to 114 days after. These recovered donors reported COVID-19 symptoms ranging from mild to severe, although no donors were hospitalized.
Results showed that the level of anti-receptor-binding domain (RBD) antibodies at the first donation varied greatly between donors. Regardless of the levels in the first donation, researchers observed a decrease in anti-RBD antibody level between the first and last donation for all donors.
Researchers calculated the level of anti-RBD antibodies at certain time points after donation and found that the decrease in anti-RBD levels did not correlate with the number of donations, indicating the decline was not a consequence of the repeated donations themselves. Rather, the decrease in anti-RBD level appeared correlated with the time elapsed between the onset of symptoms and the time of the donation (P = .0002).
Researchers then looked at the time the donations were made in four quartiles of symptom onset (range, 33-114 days). They found similar levels of antibodies between the first (33 to 53 days after symptom onset) and second (54 to 69 days) quartiles, suggesting anti-RBD response is relatively stable for the first 10 weeks, according to the researchers.
However, researchers reported a “striking observation” between the comparison of the third (70 to 84 days) and fourth (85 to 114 days) quartiles, between which they observed a 36.8% reduction the mean antibody values and a 70.1% decrease in median values.
The small sample size served as a limitation to this study.
“The antibodies disappear rapidly, so people recovering from COVID-19 who want to donate blood plasma should not wait too long once they become eligible to donate,” Bazin said in the release. “Clinicians should ideally use plasma that is collected early on after a donor’s onset of symptoms and check for the presence of antibodies before giving donor plasma to a patient.”