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Humoral Immune Response to SARS-CoV-2 in Iceland
Quick Takes
- This serosurvey study in Iceland reports that over 90% of persons tested positive with antibody assays remained seropositive 120 days after diagnosis, with no decrease of antibody levels.
- While a relationship between a humoral immune response to SARS-CoV-2 infection and protection against reinfection by this virus has been shown in rhesus macaques, it has not been established in humans.
- The low SARS-CoV-2 antibody seroprevalence in Iceland indicates that the population there is vulnerable to a second surge of COVID-19.
Study Questions:
What is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence in the population of Iceland and longitudinal changes in antibody levels within the first 4 months after SARS-CoV-2 infection?
Methods:
The investigators measured antibodies in serum samples from 30,576 persons in Iceland, using six assays (including two pan-immunoglobulin [pan-Ig] assays), and determined that the appropriate measure of seropositivity was a positive result with both pan-Ig assays. The authors tested 2,102 samples collected from 1,237 persons up to 4 months after diagnosis by a quantitative polymerase-chain-reaction (qPCR) assay. They measured antibodies in 4,222 quarantined persons who had been exposed to SARS-CoV-2 and in 23,452 persons not known to have been exposed. To test for association between each clinical characteristic and antibody levels, multiple regression analyses with the phenotype as a covariate and quantile normalized antibody levels as a response, adjusting for age, age squared, sex, and time since qPCR diagnosis, excluding the age and sex covariates when testing for association with age and sex, respectively was performed.
Results:
Of the 1,797 persons who had recovered from SARS-CoV-2 infection, 1,107 of the 1,215 who were tested (91.1%) were seropositive; antiviral antibody titers assayed by two pan-Ig assays increased during 2 months after diagnosis by qPCR and remained on a plateau for the remainder of the study. Of quarantined persons, 2.3% were seropositive; of those with unknown exposure, 0.3% were positive. The authors estimate that 0.9% of Icelanders were infected with SARS-CoV-2 and that the infection was fatal in 0.3%. They also estimate that 56% of all SARS-CoV-2 infections in Iceland had been diagnosed with qPCR, 14% had occurred in quarantined persons who had not been tested with qPCR (or who had not received a positive result, if tested), and 30% had occurred in persons outside quarantine and not tested with qPCR.
Conclusions:
The authors concluded that antiviral antibodies against SARS-CoV-2 did not decline within 4 months after diagnosis.
Perspective:
This serosurvey study in Iceland reports that over 90% of persons tested positive with antibody assays remained seropositive 120 days after diagnosis, with no decrease of antibody levels. In general, the humoral immune response is critical for the clearance of cytopathic viruses and is important for the prevention of viral reinfection. While a relationship between a humoral immune response to SARS-CoV-2 infection and protection against reinfection has been shown in rhesus macaques, it has not been established in humans. Notwithstanding the relationship between seropositivity against SARS-CoV-2 and protection against reinfection, the low SARS-CoV-2 antibody seroprevalence in Iceland indicates that the population there is vulnerable to a second surge of COVID-19.
Clinical Topics: COVID-19 Hub, Prevention
Keywords: Antibodies, Viral, Coronavirus, COVID-19, Immunity, Humoral, Phenotype, Polymerase Chain Reaction, Primary Prevention, Quarantine, Seroepidemiologic Studies, severe acute respiratory syndrome coronavirus 2
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