TY - JOUR AU - Kislaya, Irina AU - Rodrigues, Eduardo Freire AU - Borges, Vítor AU - Gomes, João AU - Sousa, Carlos AU - Almeida, José AU - Peralta-Santos, André AU - Nunes, Baltazar T1 - Comparative Effectiveness of Coronavirus Vaccine in Preventing Breakthrough Infections among Vaccinated Persons Infected with Delta and Alpha Variants T2 - Emerging Infectious Disease journal PY - 2022 VL - 28 IS - 2 SP - 331 SN - 1080-6059 AB - 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. KW - COVID-19 KW - coronavirus disease KW - SARS-CoV-2 KW - severe acute respiratory syndrome coronavirus 2 KW - Delta variant KW - Alpha variant KW - viruses KW - respiratory infections KW - zoonoses KW - vaccine-preventable diseases KW - breakthrough infections KW - mRNA vaccines KW - Portugal DO - 10.3201/eid2802.211789 UR - https://wwwnc.cdc.gov/eid/article/28/2/21-1789_article ER - End of Reference