Table 2.
Effectiveness of maternal mRNA covid-19 vaccination during pregnancy at any gestational time against delta and omicron infection and admission to hospital in infants younger than six months of age in Ontario, Canada. Data are number of infants of vaccinated mothers/total number of infants for each analysis(%) or percentage (95% confidence interval)
| Infants in case group | Infants in control group | Effectiveness of maternal vaccination | |
|---|---|---|---|
| Infection | |||
| Delta variant, primary vaccine series*† | ≤5/99 (≤5.1) | 2549/4357 (58.5) | 95 (88 to 98) |
| Omicron variant, primary vaccine series*‡ | 790/1390 (56.8) | 2880/4267 (67.5) | 45 (37 to 53) |
| Omicron variant, primary+booster vaccine seriesठ| 111/711 (15.6) | 580/1967 (29.5) | 73 (61 to 80) |
| Admission to hospital | |||
| Delta variant, primary vaccine series*† | ≤5/29 (≤17.2) | 2549/4357 (58.5) | 97 (73 to 100) |
| Omicron variant, primary vaccine series*‡ | 160/309 (51.8) | 2880/4267 (67.5) | 53 (39 to 64) |
| Omicron variant, primary+booster vaccine seriesठ| 21/170 (12.4) | 580/1967 (29.5) | 80 (64 to 89) |
Vaccine effectiveness estimated as one minus the adjusted odds ratio of maternal vaccination in cases versus controls times 100%. Multivariable logistic regression adjusted for the following variables: calendar week of testing, infant age in weeks when tested (continuous), infant sex, mother’s age at birth in years (continuous), parity, maternal SARS-CoV-2 infection preconception or during pregnancy, maternal influenza vaccination during the 2019/2020 or 2020/2021 influenza season, maternal pre-pregnancy comorbidities (diabetes mellitus, hypertension, heart disease, asthma, autoimmune disease), maternal immunosuppression, adequacy of prenatal care (Revised Graduated Prenatal Care Index), four census dissemination area-level variables (income quintile, proportion of the population who self-identify as a visible minority, proportion of the population employed in a high-risk non-health occupation, and average number of people in each dwelling to account for transmission risk), and public health unit region.
Primary covid-19 vaccination series defined as two doses up to 14 days before delivery with at least one dose after conception.
Infants tested between 31 May 2021 and 2 January 2022.
Infants tested between 22 November 2021 and 5 September 2022.
Primary plus booster covid-19 vaccination series defined as three doses up to 14 days before delivery with at least one dose after conception.