Open AccessComparative Effectiveness of Coronavirus Vaccine in Preventing Breakthrough Infections among Vaccinated Persons Infected with Delta and Alpha Variants
Author(s) -
Irina Kislaya,
Eduardo Freire Rodrigues,
Vítor Borges,
João Paulo Gomes,
Carlos Sousa,
José Pedro Almeida,
André PeraltaSantos,
Baltazar Nunes,
AUTHOR_ID
Publication year - 2022
Publication title -
emerging infectious diseases
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.54
H-Index - 226
eISSN - 1080-6059
pISSN - 1080-6040
DOI - 10.3201/eid2802.211789
Subject(s) - odds ratio , vaccination , logistic regression , delta , medicine , coronavirus , covid-19 , odds , immunology , viral load , virology , persistence (discontinuity) , virus , infectious disease (medical specialty) , geotechnical engineering , disease , engineering , aerospace engineering
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.