Characteristics and serological patterns of COVID‐19 convalescent plasma donors: optimal donors and timing of donation

Li, Ling; Tong, Xunliang; Chen, Hanwei; He, Rui; Lv, Qilu; Yang, Ru; Zhao, Lei; Wang, Jue; Xu, Haixia; Liu, Chuanqiao; Chen, Guoan; Chen, Sitian; Li, Chenyue; Qiao, Jiajia; Yang, Juntao; Wu, Yanyun; Liu, Zhong

BACKGROUND: The lack of effective treatments against the 2019 coronavirus disease (COVID‐19) has led to the exploratory use of convalescent plasma for treating COVID‐19. Case reports and case series have shown encouraging results. This study investigated SARS‐CoV‐2 antibodies and epidemiological characteristics in convalescent plasma donors, to identify criteria for donor selection. METHODS: Recovered COVID‐19 patients, aged 18‐55 years, who had experienced no symptoms for more than 2 weeks, were recruited. Donor characteristics such as disease presentations were collected and SARS‐CoV‐2 N‐specific IgM, IgG, and S‐RBD‐specific IgG levels were measured by enzyme‐linked immunosorbent assay (ELISA). RESULTS: Whereas levels of N‐specific IgM antibody declined after recovery, S‐RBD‐specific and N‐specific IgG antibodies increased after 4 weeks from the onset of symptoms, with no significant correlation to age, sex, or ABO blood type. Donors with the disease presentation of fever exceeding 38.5°C or lasting longer than 3 days exhibited higher levels of S‐RBD‐specific IgG antibodies at the time of donation. Of the 49 convalescent plasma donors, 90% had an S‐RBD‐specific IgG titer of ≥1:160 and 78% had a titer of ≥1:640 at the time of plasma donation. Of the 30 convalescent plasma donors, who had donated plasma later than 28 days after the onset of symptoms and had a disease presentation of fever lasting longer than 3 days or a body temperature exceeding 38.5°C, 100% had an S‐RBD‐specific IgG titer of ≥1:160 and 93% had a titer of ≥1:640. CONCLUSION: This study indicates that the S‐RBD‐specific IgG antibody reaches higher levels after 4 weeks from the onset of COVID‐19 symptoms. We recommend the following selection criteria for optimal donation of COVID‐19 convalescent plasma: 28 days after the onset of symptoms and with a disease presentation of fever lasting longer than 3 days or a body temperature exceeding 38.5°C. Selection based on these criteria can ensure a high likelihood of achieving sufficiently high S‐RBD‐specific IgG titers.