Abstract
INTRODUCTION: The reduction of lung capillary blood volume (Vc) had been identified as the microvascular injury mostly underlying the respiratory Long-COVID syndrome following post-COVID-19 pneumonia. The same kind of injury have been recently also found in several individuals after milder paucisymptomatic SARS-CoV-2 infections. Though current guidelines strongly recommend vac-cination, studies aimed to investigate the in vivo protection of anti-SARS-CoV-2 vaccines on lung microvascular targets still are missing to our best knowledge. AIM: to assess the protection of mRNA vaccines from the reduction of lung capillary blood volume (Vc) caused by pauci-symptomatic SARS.CoV-2 infections in vaccinated compared to unvaccinated individuals. METHODS: Non-smoking individuals with recent paucisymptomatic SARS-CoV-2 infection were divided into vaccinated and unvaccinated groups. Lung function parameters, including single-breath diffusing capacity and microvascular blood volume, were compared between groups. RESULTS: fifty vaccinated and twenty-five unvaccinated well-matched individuals were studied. Differently than usual lung function parameters, only the single-breath simultaneous assessment of sDLCO, sDLNO/sDLCO ratio and Vc allowed to identify the occurrence of the lung microvascular injury with high sensitivity and specificity (p<0.001). CONCLUSION: mRNA vaccines proved to exert a high protection from the loss of lung capillary blood volume (Vc) induced by SARS.CoV-2 paucisymptomatic infections (p<0.001). The availability of this non-invasive investigational model should be regarded as a very helpful tool for assessing and comparing in vivo the protective effect of mRNA vaccines on the human microvascular structures of the deep lung.