SARS-CoV-2 Specific Cellular and Humoral Immunities Found One Year After Disease Onset
With the unabated pandemic of the SARS-CoV-2 betacoronavirus nearing its second anniversary, the goal of achieving herd immunity remains debated.
Researchers in China recently addressed this challenge in a study published by the journal Clinical Infectious Diseases on October 5, 2021, which is excerpted below.
'The attainment of protective population-level immunity requires the induction of long-term immunological memory by SARS-CoV-2 infection or COVID-19 vaccination, as this is crucial for protection upon coronavirus re-exposure and reduction of human-to-human transmissions.'
For example, the UK's Public Health England reported that seroprevalence data on October 7, 2021, indicates that approximately 98% of blood donors aged 17 and over have antibodies to SARS-CoV-2 from either virus infection or COVID-19 vaccination.
These researchers presented a comprehensive longitudinal analysis of SARS-CoV-2- specific humoral and T-cell responses in COVID-19 convalescents who provided follow-up samples at six months and/or 12 months post-symptom onset.
No participants in this study reported reinfection during their convalescent phase.
The anti-SARS-CoV-2 antibody titers in convalescents were found to be very durable.
The percentages of NAbpositive COVID-19 convalescents were both above 95% at 6m and 12m post-infection, without a significant decline in NAb titer over time.
The IgG against spike RBD, as determined by ELISA and MCLIA, also persisted among nearly 95% of patients at 12m post-infection.
This finding is in line with previous reports on the relatively stable humoral immunity within the COVID-19 convalescent individuals for up to 6-8 months.
However, this study found an even higher percentage of convalescents who were positive for anti-SARS-CoV-2 antibodies, supported by the consistency among three different antibody detection methods (NAb, ELISA IgG and MCLIA IgG).
Although a significant IgG level decline was also detected among the convalescents in this study, the percentage of IgG-positive individuals was sustained between 6m and 12m.
In addition, the SARS-CoV-2 NAb titers of the convalescents did not differ significantly between 6m and 12m.
Considering the declining trend in NAb titer among over 40% (27/57) of the convalescents, evaluating the durability of establishing humoral immunity through SARS-CoV-2 infection needs further observation.
In summary, these researchers stated 'Our data demonstrate that SARS-CoV-2-specific humoral immunity is present within ~95% of convalescents and T-cell memory against at least one viral antigen is measurable among ~90% of subjects at 12m post-infection.'
'From 6m to 12m post-infection, anti-SARS-CoV-2 IgG and IgM levels show a declining trend, but the levels of NAb and CD8+ and CD4+ T cells against SARS-CoV-2 are durable.'
'These findings are encouraging in relation to the longevity of immune memory against this novel virus and indicate that these sustained immune components, which persist, among most SARS-CoV-2-infected individuals, may contribute to protection against reinfection.'
The study was supported by the National Natural Science Foundation of China, the Major Special Projects for Infectious Disease Research of China, and CAMS Research Units of Adaptive Evolution and Control of Emerging Viruses. In addition, the study authors declared no competing interests.