Post-vaccination COVID-19 Spike-Specific IgA antibody levels in vaccinee nasopharyngeal samples

Increased COVID-19-specific secretary IgA antibody levels in the respiratory tract are required for inhibiting early COVID-19 virion particle attachment to ACE-2 receptors and primary virus replication. Because all COVID-19 vaccines are administered parenterally, it has been thought that the vaccine might not elicit sufficient mucosal immunity (1). The purpose of this study was to determine the level of IgA antibodies in respiratory samples from vaccinees. Twenty-ninenasopharyngeal swabs were collected from healthy participants who had received at least two doses of a different COVID-19 vaccination. Rt-PCR confirmed that all samples were negative for COVID-19. A quantitative ELISA kit with defined calibrators (0-25) ng/ml coated with recombinant 2019-nCoV Spike protein (antigen) was used to measure IgA antibody concentrations per sample. The results revealed that COVID-19 spike IgA was present at a lower level in the majority of the samples (86.2%), with a mean IgA level of 0.01 ng/ml. Only four samples had higher IgA levels, which accounted for 13.8%. (Fig. 1). Three subjects had elevated IgA levels, ranging from 0.5 to 1.5 ng/m. One individual had a boosted IgA level of 3.4 ng/ml, which retested negative in COVID-19 Rt-PCR and appeared to be a recently recovered asymptomatic COVID-19case. The result explains why COVID-19 vaccines failed to prevent virus transmission and infection, because the vaccines failed to elicit protective mucosal immunity in the form of highly protective secretary IgA antibodies in vaccinees. This is because the current COVID-19 vaccines are administered parentally rather than through the mucosal portal via oral immunization or nasal spray delivery. Thus, there is a need for second or third mucosal (nasal/oral) COVID-19 vaccine doses which might imitate natural infection by boosting mucosal IgA levels. This would help in reducing the number of healthy carriers and, in the long run, in eradicating the existing circulating virus.