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Volume 28, Number 2—February 2022

Comparative Effectiveness of Coronavirus Vaccine in Preventing Breakthrough Infections among Vaccinated Persons Infected with Delta and Alpha Variants

Irina Kislaya1Comments to Author , Eduardo Freire Rodrigues1, Vítor Borges, João P. Gomes, Carlos Sousa, José P. Almeida, André Peralta-Santos, Baltazar Nunes, and PT-COVID-19 Group2
Author affiliations: Instituto Nacional de Saúde Doutor Ricardo Jorge, Lisbon, Portugal (I. Kislaya, V. Borges, J.P. Gomes, B. Nunes); Direção-Geral da Saúde, Lisbon (E.F. Rodrigues, A. Peralta-Santos); Unilabs, Porto, Portugal (C. Sousa, J.P. Almeida)

Main Article

Table 3

Ct values based on mean reverse-transcription PCR Ct values for nucleocapsid and open reading frame 1ab genes, stratified by vaccination status and severe acute respiratory syndrome coronavirus 2 variant of concern, and confounder-adjusted mean differences, Portugal, epidemiologic weeks 20–26 (May 17–July 4), 2021

Vaccination status Delta (B.1.617.2, mean (SD) Alpha (B.1.1.7), mean (SD) Mean difference,* Delta vs. Alpha (95% CI)
Overall 16.4 (5.0) 18.7 (5.3) −2.10 (−2.74 to −1.47)
Unvaccinated 16.5 (4.9) 18.4 (5.2) −1.66 (−2.37 to −0.95)
1 dose (<14 d) 15.7 (4.9) 19.2 (5.6) −1.42 (−3.07 to 0.23)
1 dose (>14 d) or 2 doses (<14 d)† 16.1 (5.0) 20.0 (5.6) −1.88 (−3.77 to −0.003)
2 doses (>14 d)‡ 17.7 (5.7) 21.8 (5.7) −2.24 (−4.8 to 0.32)
Mean difference, partial vaccinated vs. unvaccinated* −0.15 (−0.99 to 0.96) 1.87 (0.2 to 3.53)
Mean difference, complete vaccinated vs. unvaccinated* 2.24 (0.85 to 3.64) 4.49 (2.07 to 6.91)

*Mean difference and respective 95% CIs estimated by linear regression model adjusted to sex, age group, and week of diagnosis. †Partial vaccination. ‡Complete vaccination.

Main Article

1These first authors contributed equally to this article.

2Members of the PT-Covid-19 Group are listed at the end of this article.

Page created: November 29, 2021
Page updated: January 22, 2022
Page reviewed: January 22, 2022
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