Figure 1. Rate Ratios of Positive PCR Tests in Contacts, According to Time since the Second Vaccination in Index Patients and Contacts, SARS-CoV-2 Variant, and Vaccine Type.

The rate ratios of positive polymerase-chain-reaction (PCR) tests in contacts according to index-patient vaccination status (Panel A) and contact vaccination status (Panel B) are shown. The shaded areas indicate 95% confidence intervals. There was no evidence that fitting different rates according to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant for the change in protection over weeks since the second vaccination improved the model fit. The broad confidence intervals for the alpha variant show that relatively few persons who were vaccinated twice were infected before the delta variant became the dominant lineage.