Retrospective 28,167 patients in the USA demonstrating confounding. The large difference shown in Figure 1 at day 0 indicates that the groups are not comparable (32 control hospitalizations versus 0 for paxlovid at day 0) and suggests immortal time bias / confounding by indication. For example, patients in more serious condition may be sent for admission rather than to the pharmacy for paxlovid. ~60% of the difference between the groups at day 28 exists at day 0, and close to 100% by day 4. Confounding may also arise due to inclusion of contraindicated patients in the control group, only partially investigated in sensitivity analysis. Patients that seek out paxlovid may also differ in risk to those that do not.Authors also note that "The post-hoc sensitivity analysis derived from a cohort of only patients with an observed SARS-CoV-2 postitive [sic] test date was 70% smaller than the primary cohort, and the point estimate for a nirmatrelvir-ritonavir association with reduced 28-day hospitalisation did not reach statistical significance."[Hoertel] find that over 50% of patients that died had a contraindication for the use of Paxlovid. Retrospective studies that do not exclude contraindicated patients may significantly overestimate efficacy.