Cosmos Study

Maternal RSV Vaccine Effective in Reducing RSV Infections and Hospitalizations in Infants

January 21, 2025

Team A:Kersten Bartelt, RNJacob GasserEmily Higgs

Team B:Matthew Gracianette, MDEric Barkley

Key Findings

Babies born to mothers who receive the respiratory syncytial virus (RSV) vaccine during pregnancy are 61% less likely to have an RSV infection compared to babies whose mother did not receive the RSV vaccine.
Babies born to mothers who receive the RSV vaccine during pregnancy are 78% less likely to be admitted to the hospital with RSV compared to babies whose mother did not receive the RSV vaccine.

In 2023, the U.S. Food and Drug Administration (FDA) approved a vaccine for respiratory syncytial virus (RSV) to be administered during pregnancy to prevent RSV in infants.¹ To evaluate the real-world effectiveness of this new vaccine, we identified 393,561 babies born to mothers between September 2023 and May 2024 with 7.7% of mothers having a documented RSV vaccine. We then matched vaccinated mothers to unvaccinated mothers in a ratio of 1:4 by birth month and gestational age of the infant at birth, resulting in a study population of 58,060 births. We adjusted for maternal age, maternal comorbidities, Social Vulnerability Index quintile, rural or urban status, census region, neonatal infection in first 30 days of life, and prematurity.

We found that babies born to mothers who received the RSV vaccine during pregnancy were 61% less likely to have an RSV infection compared to those whose mother did not receive the RSV vaccine, as seen in Figure 1. Similarly, babies born to mothers who received the RSV vaccine during pregnancy were 78% less likely to be admitted to the hospital with RSV compared to those born to mothers who did not receive the RSV vaccine.

Figure 1

Likelihood of Infant RSV Infection or Hospitalization by Maternal RSV Vaccination Status

Figure 1. The likelihood of a baby having an RSV infection or hospital admission by whether their mother received the RSV vaccine during pregnancy.

Original Publication Date: January 21, 2025
Last Updated: January 27, 2025

These data come from Cosmos, a dataset created in collaboration with a community of Epic health systems representing more than 289 million patient records from 1,600 hospitals and more than 37,000 clinics from all 50 states, Lebanon, and Saudi Arabia. This study was completed by two teams that worked independently, each composed of a clinician and research scientists. The two teams came to similar conclusions. Graphics by Brian Olson.

References

FDA approves first vaccine for pregnant individuals to prevent RSV in infants. U.S. Food and Drug Administration. September 21, 2023. https://www.fda.gov/news-events/press-announcements/fda-approves-first-vaccine-pregnant-individuals-prevent-rsv-infants. Accessed December 17, 2024.

Data Definitions

Study period: Births between 9/1/2023 and 5/31/2024

Study population

A birth that occurred in the United States during the study period with a link to a mother’s record in Cosmos.
Inclusions:

A newborn face-to-face visit after six months of age
A vaccine registry query on the mom’s chart two weeks before birth or later
A vaccine registry query on the baby’s chart after 6-months of age

Exclusions:

Gestational age less than 32 weeks or greater than 44 weeks
Births to mothers younger than 18
Babies who received any RSV vaccine with a CVX code of 303, 304, 305, 306, 307, 314, 315, or 326 in the first year after birth
Mothers who received an RSV vaccine not indicated for pregnancy with a CVX code of 303, 306, 307, 315, or 326

RSV vaccine: A vaccine with CVX code 304, 305, or 314 given to the mother during pregnancy

RSV: In the first six months after birth, a diagnosis with ICD-10-CM code J12.1*, J20.5*, J21.0*, or B97.4* or a lab with an abnormal result or value of “Detected” with LOINC code 14129-1, 17520-8, 55100-2, 88527-7, 91782-3, 91785-6, 101425-7, 77022-2, 88595-4, 91795-5, 101426-5, 77023-0, 88597-0, 91794-8, 101298-8, 76088-4, 76089-2, 82176-9, 85479-4, 91133-9, 92131-2, 92957-0, 30075-6, 101982-7, 41456-5, 80597-8, 88204-3, 80598-6, 88202-7, 30076-4, 40987-0, 88528-5, 60271-4, 40988-8, 31949-1, 31950-9, 32040-8, 33045-6, 50329-2, 5874-3, 5875-0, 5876-8, 5877-6, 68966-1, 72885-7, 77389-5, 77390-3, or 88909-7

Confounders

RUCA: Metropolitan, Micropolitan, Small Town, Rural
Census Region: West, South, Midwest, Northeast
Social Vulnerability Index quintile
Maternal age: 18-24, 25-34, 35+
Baby infection: A diagnosis with ICD-10-CM code P23.1, P39.1, P00.82, A32*, P37.2, P35.0, A50*, B58*, P37.1, or P35.4 in first 30 days after birth
Maternal comorbidities:

Autoimmune: A diagnosis with ICD-10-CM code M32.9, O99.891, R76.0, D68.61, M06.9, O99.11*, O99.12*, or L40.5*
Infection: A diagnosis with ICD-10-CM code O98*, O99.82*, N76.0, A56.0*, A56.8, B08.3, A54.0*, Z22.330, B16*, B18.0, B18.1, B17.1*, B19.1*, B18.2, B19.2*, B20, B97.7, A69.2*, B06*, A51*, A52*, A59*, or A92.5
Hypertension: A diagnosis with ICD-10-CM code O10*-O13*
Diabetes: A diagnosis with ICD-10-CM code O24.1* or O24.4*

Prematurity: Gestational age before 37 weeks

RUCA: Rural-Urban Commuting Area is a classification of geographic areas based on population density, urbanization, and daily commuting. It ranges from 1 to 10, with lower values indicating more urban areas and higher values indicating more rural areas.

Social Vulnerability Index: The social vulnerability quintile for the ZIP Code of the patient’s most recent address.

Model specifications: Births where the mother received the RSV vaccine were matched to unvaccinated mothers 1:4, matching on the calendar month of birth and gestational age in weeks.
Vaccine effectiveness was calculated from the hazard ratio from a Cox proportional hazards regression.