We developed a case–case study to compare mRNA vaccine effectiveness against Delta versus Alpha coronavirus variants. We used data on 2,097 case-patients with PCR-positive severe acute respiratory syndrome coronavirus 2 infections reported in Portugal during May–July 2021. We estimated the odds of vaccine breakthrough infection in Delta-infected versus Alpha-infected patients by using conditional logistic regression adjusted for age group and sex and matched by the week of diagnosis. We compared reverse-transcription PCR cycle threshold values by vaccination status and variant as an indirect measure of viral load. We found significantly higher odds of vaccine breakthrough infection in Delta-infected patients than in Alpha-infected patients (odds ratio 1.96 [95% CI 1.22–3.14]), suggesting lower effectiveness of the mRNA vaccines in preventing infection with the Delta variant. We estimated lower mean cycle threshold values for the Delta cases (mean difference −2.10 [95% CI −2.74 to −1.47]), suggesting higher infectiousness than the Alpha variant.
【저자키워드】 COVID-19, coronavirus disease, severe acute respiratory syndrome coronavirus 2, viruses, respiratory infections, zoonoses, SARS-CoV-2, delta variant, mRNA vaccines, breakthrough infections, Alpha variant, vaccine-preventable diseases, Portugal, 【초록키워드】 Vaccine, coronavirus, vaccination, mRNA vaccine, variant, Infection, Delta, Diagnosis, Sex, delta variant, mRNA vaccines, Viral, Viral load, Patient, Effectiveness, Logistic regression, Alpha, age, Breakthrough infection, Alpha variant, respiratory, Portugal, coronavirus variants, Cycle threshold value, Odds ratio, Vaccination Status, acute respiratory syndrome, PCR-positive, mean difference, threshold value, PCR cycle, reported, adjusted, significantly higher, preventing infection, used data, 【제목키워드】 Delta, Comparative, Person, Preventing,