NPPA and Klebsiella pneumonia: Our group and others have demonstrated that acetate, a gut microbiota metabolite, contributes to the control of pulmonary infection induced by the pathogen Klebsiella pneumonia in mice.22–24 Accordingly, we observed reduced serum acetate levels in post-COVID Kp-infected mice compared to those in post-COVID non-infected (vehicle) mice (Figure 4f).