Question Number: 187
PDR Number: SQ22-000557
Date Submitted: 21/11/2022
Department or Body: Department of Health

Question 96 Vaccination and infection induce immune responses to pathogens in the lymphoid system including mucosa-associated lymphoid tissues. Lung based responses can occur by a number of mechanisms, some of which involve antibodies. Resident memory lymphocytes (T cells and B cells) in the lung can rapidly generate both humoral and cellular immune responses to respiratory pathogens upon exposure to the pathogen (available at: www.frontiersin.org/articles/10.3389/fimmu.2021.738955/full). There are also plasma immune cells beneath basement membranes of respiratory epithelia in contact with the external environment. Antibodies are synthesised by plasma cells and then transferred by binding to a transporter protein, to the apical surface of the respiratory tract through transcytosis. In this way, antibodies are transported across epithelia into the lumens of the respiratory tract (available at: www.ncbi.nlm.nih.gov/books/NBK27162) to fight viruses or bacteria in the lung. Cellular immunity is also activated by infection. The local resident immune cells such as dendritic cells send signals to other immune cells and secret cytokines to recruit T cells to the site of infection to eliminate a pathogen (available at: www.pubmed.ncbi.nlm.nih.gov/27890913). Question 96 Monkeys and other animal models do not replicate exactly the same symptoms and pathology of COVID infections as humans. Animal models develop milder lung diseases than humans from COVID-19 infection. However, the monkey study clearly demonstrated reduced or no viral RNA in bronchoalveolar lavage and oropharyngeal swabs in the vaccinated group compared to the unvaccinated group after virus challenge. The vaccinated monkeys also developed high titres of virus neutralising antibodies and cellular immunity against SARS-CoV-2 virus. IgG titres in the monkey study decreased by 3-5-fold 35 days after the last vaccine dose, but the titres were still between ~4000 and ~6000 U/mL. The IgG response decreases over time after vaccination with any vaccines. Most importantly, the monkeys challenged with the virus 55 days after the 2nd vaccine dose had lower or no viral RNA in bronchoalveolar lavage and oropharyngeal swab in the vaccinated group when compared with the unvaccinated group and significantly lower lung inflammation score. For any vaccines, the dose per body weight does not have a linear relationship to the duration of immune response.