Rapid Decay of IgA and IgM Following COVID-19 Infection

Doctor hand holding positive Coronavirus or Covid-19 rapid test
Study authors measured the levels of immunoglobulin M, IgG, and IgA in healthcare workers, and observed fast decay of 2 antibodies which has implications for further seroprevalence studies.

A decline of immunoglobulin (Ig)A and IgM after coronavirus disease 2019 (COVID-19) was seen in healthcare workers in Spain, according to data from a cross-sectional study published in The Journal of Infectious Diseases.

Healthcare workers (N=566) at Hospital Clínic de Barcelona, Barcelona, Spain, were randomly selected for the study. Participants underwent a nasopharyngeal swab and provided a blood sample at baseline, 1 month, and 3 months. The swabs were assessed by real time polymerase chain reaction (RT-PCR) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the blood samples were screened for antibodies.

At baseline, 11.5% (65/566) of participants had evidence of a previous SARS-CoV-2 infection. Among the workers who had no evidence of an infection, 71.7% were women, 53.5% had a mean age of 42 years, 11% reported previous COVID-19 symptoms, 21.2% had comorbidities, and 76.4% worked directly with patients with COVID-19.

At 1 month, 14.9% of participants had evidence of a previous SARS-CoV-2 infection. In total, 10.1% of samples were positive for IgM, 11.3% were positive for IgG, and 11.5% were positive for IgA. Among the participants previously uninfected, 5% had been newly infected.

The likelihood of receiving a positive COVID-19 test was associated with the participant’s position within the hospital. Lab and other technicians were at increased infection risk (odds ratio [OR], 13.3; 95% CI, 1.47-115.76; P =.048).

Among samples that were COVID-19 positive at month 1, 77.55% has seroreverted for IgM, 3.70% for IgG, and 24.53% for IgA by month 3. These rates equated to reversion of at least 1 antibody among 6.1% of individuals. IgG levels increased among 28 individuals between baseline and 1 month and among 6 individuals between month 1 and month 3.

Antibody decay rates from baseline to month 3 was 0.14 (95% CI, 0.11-0.18) for IgM, 0.66 (95% CI, 0.53-0.82) for IgG, and 0.12 (95% CI, 0.09-0.16) for IgA. Seroreversion was projected to occur at 1.95 months (95% CI, 1.74-2.22; P <.0001) for IgM, 19.41 month (95% CI, 12.84-39.75; P <.0001) for IgG, and 1.95 months (95% CI, 1.71-2.25; P <.0001) for IgA.

Stratified by symptoms, levels of IgA were higher among healthcare workers who had COVID-19 compatible symptoms (P =.0008) and levels of IgM were higher among those who experienced symptoms for more than 10 days (P =.0019). Having a COVID-19 compatible symptom during the follow-up month was associated with a SARS-CoV-2 infection between month 0 and 1 (OR, 6.55; 95% CI, 2.77-14.44; P <.0001).

These findings may have been limited by the choice to use only 1 antigen for antibody testing.

“IgA levels are higher in symptomatic individuals compared to asymptomatic [individuals], and IgM levels positively correlate with the duration of symptoms,” investigators concluded. IgA and IgM antibodies decayed rapidly after COVID-19 infection, especially among asymptomatic individuals or those who experienced mild symptoms.


Moncunill G, Mayor A, Santano R, et al. SARS-CoV-2 seroprevalence and antibody kinetics among health care workers in a Spanish hospital after three months of follow-up. J Infect Dis. Posted online November 11, 2020. doi:10.1093/infdis/jiaa696.