- Simeone, Regina;
- Zambrano, Laura;
- Halasa, Natasha;
- Fleming-Dutra, Katherine;
- Newhams, Margaret;
- Wu, Michael;
- Orzel-Lockwood, Amber;
- Kamidani, Satoshi;
- Pannaraj, Pia;
- Irby, Katherine;
- Maddux, Aline;
- Hobbs, Charlotte;
- Cameron, Melissa;
- Boom, Julie;
- Sahni, Leila;
- Kong, Michele;
- Nofziger, Ryan;
- Schuster, Jennifer;
- Crandall, Hillary;
- Hume, Janet;
- Staat, Mary;
- Mack, Elizabeth;
- Bradford, Tamara;
- Heidemann, Sabrina;
- Levy, Emily;
- Gertz, Shira;
- Bhumbra, Samina;
- Walker, Tracie;
- Bline, Katherine;
- Michelson, Kelly;
- Zinter, Matt;
- Flori, Heidi;
- Campbell, Angela;
- Randolph, Adrienne
Infants aged <6 months are not eligible for COVID-19 vaccination. Vaccination during pregnancy has been associated with protection against infant COVID-19-related hospitalization. The Overcoming COVID-19 Network conducted a case-control study during March 9, 2022-May 31, 2023, to evaluate the effectiveness of maternal receipt of a COVID-19 vaccine dose (vaccine effectiveness [VE]) during pregnancy against COVID-19-related hospitalization in infants aged <6 months and a subset of infants aged <3 months. VE was calculated as (1 - adjusted odds ratio) x 100% among all infants aged <6 months and <3 months. Case-patients (infants hospitalized for COVID-19 outside of birth hospitalization and who had a positive SARS-CoV-2 test result) and control patients (infants hospitalized for COVID-19-like illness with a negative SARS-CoV-2 test result) were compared. Odds ratios were determined using multivariable logistic regression, comparing the odds of receipt of a maternal COVID-19 vaccine dose (completion of a 2-dose vaccination series or a third or higher dose) during pregnancy with maternal nonvaccination between case- and control patients. VE of maternal vaccination during pregnancy against COVID-19-related hospitalization was 35% (95% CI = 15%-51%) among infants aged <6 months and 54% (95% CI = 32%-68%) among infants aged <3 months. Intensive care unit admissions occurred in 23% of all case-patients, and invasive mechanical ventilation was more common among infants of unvaccinated (9%) compared with vaccinated mothers (1%) (p = 0.02). Maternal vaccination during pregnancy provides some protection against COVID-19-related hospitalizations among infants, particularly those aged <3 months. Expectant mothers should remain current with COVID-19 vaccination to protect themselves and their infants from hospitalization and severe outcomes associated with COVID-19.