Protection against disease and protection against infection (25/01/22 19:28:18)
that the best available protection would be a full vaccination plus a subsequent infection, combatted by natural mechanisms. Thie vaccine would provide IgG, and safety during the process of natural infection, which would provide additional later protection by means of secretory IgA.
(this is old knowledge - say the 1970s or earlier).
"The current challenge in vaccine design is to induce long-lasting systemic and mucosal protection against the vaccine strains, but also against drifted and shifted strains. Most antiviral vaccines are now administered intramuscularly or subcutaneously, and they might not always induce a mucosal immune response (van Riet et al., 2012; Bagga et al., 2015). It has been shown that IgA antibodies on mucosal surfaces play a more relevant role than IgG for protection from influenza A virus infection and for cross-protective immunity against multiple viral hemagglutinin subtypes (Okuya et al., 2020). More recently, it has been shown in mice that immunization with MERS-CoV S1 subunit and full-length Spike protein elicited high levels of S1-specific neutralizing IgA response. However, MERS-CoV neutralizing IgA antibodies in the broncho-alveolar lavage fluid were only induced by intranasal and sublingual administration but not by intramuscular administration (Kim et al., 2019)."
"Being a mucosal targeted virus, SARS-CoV-2 secretory IgA plays an important role in the early defense and viral containment. As we specified above, IgA serum concentrations decreased one month after the onset of symptoms, while neutralizing IgA remained detectable in saliva for a longer time (Burgess et al., 2020). A human monoclonal IgA antibody cross-reactive with SARS-CoV and SARS-CoV-2 spike proteins was able to neutralize SARS-Cov-2 infection in vitro when converted to sIgA (Ejemel et al., 2020). Secretory IgA in the gut and monomeric IgA in the serum are clonally related (Iversen et al., 2017). sIgA specific for SARS-CoV-2 has been detected in the milk (Fox et al., 2020) of SARS-CoV-2 infected mothers, thus demonstrating that sIgA is produced in response to the infection and it is passed to the neonate for protection. It has been suggested that also in adults the measurement of SARS-CoV-2 sIgA might help to identify those individuals that, protected by sIgA, did not develop symptoms and disease (Burgess et al., 2020)."
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