Volume 28, Number 2—February 2022
Research
Comparative Effectiveness of Coronavirus Vaccine in Preventing Breakthrough Infections among Vaccinated Persons Infected with Delta and Alpha Variants
Irina Kislaya1
, Eduardo Freire Rodrigues1, Vítor Borges, João P. Gomes, Carlos Sousa, José P. Almeida, André Peralta-Santos, Baltazar Nunes, and PT-COVID-19 Group2
, Eduardo Freire Rodrigues1, Vítor Borges, João P. Gomes, Carlos Sousa, José P. Almeida, André Peralta-Santos, Baltazar Nunes, and PT-COVID-19 Group2
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.
1These first authors contributed equally to this article.
2Members of the PT-Covid-19 Group are listed at the end of this article.
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