Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Immunoglobulin G (IgG) high throughput serology assays have so far been used mainly to conduct seroprevalence studies in large cohorts to help public health decision making.
All recent seroprevalence studies only examined the detection of antibodies from natural SARS-CoV-2 infection. While most of the vaccine candidates produced detectable antibody levels in serological research assays in early phase trials, it is not clear how existing high-throughput commercial assays can detect vaccine-induced antibodies in the lab.
Vaccine-induced antibody detection in the case of varicella varies with different commercial kits compared to the detection of antibodies produced via natural infection, which are more potent.
Determining the ability of commercial assays to detect vaccine-induced antibodies
A recent study by researchers from Canada aimed to examine the ability of commercial assays to detect vaccine-induced antibodies and recognize the vaccination response.
The study cohort included residents of long-term care facilities and healthcare workers receiving the mRNA-1273 and BNT162b2 vaccines, respectively. The study is published on the preprint server, medRxiv*.
The study had a total of 225 participants, of which 177 participants received BNT162b2 and 48 participants mRNA-1273. The participants' median age was 41 years, and 66-78% of them were female. Secondary outcomes of the study were the description of post-vaccination response and correlation with neutralizing antibody titers.
Serum was collected pre-vaccination (BNT162b2 group), 2-weeks after vaccination (both groups), and before the 2nd dose in both groups. Serum samples were tested for SARS-CoV-2 IgG using 4 commercial assays - Abbott Architect SARS-CoV-2 IgG 62 II Quant, Abbott Architect SARS-CoV-2 IgG, GenScript cPASS, and DiaSorin Liaison Trimeric S IgG) to detect VIAs.
Nucleocapsid IgG was found in 4.1% of the BNT162b2 (baseline) samples and 21.9% of the mRNA-1273 (2-weeks after the first dose) sample. All anti-spike assays were able to detect post-vaccination antibodies, with an average increase of 87.2% (range 73.8-94.3%) in the BNT162b2 samples and 25.2% (range 23.8-26.7%) in the mRNA-1273 samples between the 1st and last sampling time points. Neutralizing antibodies were detected for both vaccine arms at all post-vaccine timepoints with an increase in titers over time.
"Quantitative titers in the mRNA-1273 group were found to be significantly higher among participants who were COVID-19 recovered compared to those with no history of laboratory-confirmed COVID-19 infection."
Results highlight the importance of continued prevention measures after the first vaccine dose
This study's findings demonstrate that vaccine-induced antibodies produced by FDA-approved SARS-CoV-2 mRNA vaccines, BNT162b2 and mRNA-1273, are detectable using commercial high-throughput assays used currently in clinical laboratories. As was expected, detectable antibodies were present only in assays designed to identify IgG directed against the viral spike protein and not IgG directed against the nucleocapsid protein.
"Overall, our data demonstrate significant increases in the median titer of anti-S IgG by all assays evaluated in both mRNA vaccine groups, except for the RBD IgG among the mRNA-1273 group, which did not measure levels from baseline but only from two weeks post-vaccination."
Anti-spike, vaccine-induced antibodies were detected within 10 days after receiving the first dose of an mRNA vaccine. The assays were also able to show that the vaccine-induced SARS-CoV-2 IgG increases over time. Even before the second vaccination dose, the neutralizing antibodies were detectable in 73-89% of the participants, which shows that most individuals are protected to some degree from subsequent infection by the first dose of vaccination.
However, a considerable subpopulation did not produce neutralizing antibodies before the second dose, highlighting the importance of the continued measures to prevent SARS-CoV-2 infection after receiving the first dose of the vaccine, especially in individuals with no detectable levels of neutralizing antibodies.
"Our current study adds to the literature by confirming the detection of these IgG binding and also functional nAbs using commercial kits from other companies likely to be adopted by large-volume clinical laboratories."
*Important Notice
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.