Elevated serum IgA following SARS-CoV-2 vaccination in a cohort of high-risk first responders
The study recruited first responders and other personnel from police, fire, and emergency medicine services (EMS). Details regarding the recruitment and study participants have already been published.seven. Participants were asked at baseline and at follow-up regarding prior exposure to SARS-CoV-2, periods of work quarantine, symptomatic illnesses potentially consistent with COVID-19, and confirmed diagnoses of COVID-19.
We categorized individuals based on serological and clinical evidence of SARS-CoV-2 infection and disease as follows: certain COVID-19 includes participants with a positive RT-PCR or COVID-19 antigen test OR a positive IgG antibody associated with a history of exposure to someone with COVID-19 and a history of symptoms consistent with COVID-19; Likely COVID-19 includes participants with positive IgA or IgG antibodies combined with a history of symptoms consistent with COVID-19 OR a history of exposure to someone with COVID-19 AND a history of symptoms consistent with COVID-19; Possible COVID-19 includes participants with a history of exposure to someone with COVID-19 and a history of symptoms consistent with COVID-19 without positive IgG or IgA antibodies; Defined asymptomatic infection includes participants with positive IgA or IgG antibodies with a history of exposure to a person with COVID-19 without a history of symptoms consistent with COVID-19 OR a positive IgG antibody with no history of exposure to a person with COVID-19 19 and no history of symptoms consistent with COVID-19; Possible asymptomatic infection includes participants with positive IgA antibodies alone with no history of exposure to someone with COVID-19 and no history of symptoms consistent with COVID-19 and No evidence of SARS-CoV-2 or COVID-19 infection includes participants for whom all antibodies were negative and there was neither a history of exposure to someone with COVID-19 nor a history of symptoms consistent with COVID-19. Participants were ranked according to the last assessment before vaccination.
Participants’ sera were tested at three time points (baseline, 2-3 months, 6 months) at ICON Laboratories using the Abbott Architect Anti-SARS-CoV2 Microchemiluminescent Microparticle (MIA) Immunoassay for IgG (anti-nucleocapsid protein, anti-N), Euroimmun Anti-SARS-CoV-2 ELISA for IgG (anti-S1 domain of the tip, anti-S) and Euroimmun Anti-SARS-CoV2 ELISA for IgA (anti-S1 domain of the tip). Results for anti-N IgG were classified as positive or negative based on a signal/threshold index greater than or equal to 1.4 for positive results. Associations with anti-S IgG and IgA were assessed on the basis of an optical density ratio greater than or equal to 1.1 corresponding to positive tests according to the manufacturer’s specifications.
Vaccination status was defined as complete if the participant had received a complete series at least 14 days before collection. The vaccination was qualified as partial if from 14 days before the collection, they had received only one dose out of 2. All the others classified as not vaccinated. Individuals who completed a series at least 14 days prior to the 2nd collection were assessed on their response at the time of the 2nd collection only.
To assess the impact of prior SARS-CoV-2 infection on vaccine response, we compared those classified as definite COVID-19, probable COVID-19, possible COVID-19, or definite asymptomatic infection to those classified as no evidence of SARS-CoV-2 or COVID-19 infection. The percentage of positive antibodies by type was summarized by type of vaccine, vaccination status and history of infection or disease classified.
Data management and statistical analyzes were performed using SAS® Version 9.4 (SAS Institute Inc., Cary, NC, USA). The chi-square test was used to assess differences in antibody positivity based on exposure and disease categories and prior vaccine receipt. Medians were calculated and non-Wilcoxon rank sum tests were performed to assess differences in IgG and IgA ratios based on COVID-19 history and vaccine manufacturer. Data visualization was done in R with the ggplot2 package.
IRB approval was obtained from Western IRB, Protocol No. 20201662. Informed consent was obtained from all participants at the time of study enrollment. All study recruitment and laboratory testing was performed in accordance with applicable guidelines and regulations.