November 11, 2014

How safe is receiving Tdap vaccine during pregnancy?

JAMA study shows no raised risk for preterm birth or low birthweight in Vaccine Safety Datalink

Newborns are vulnerable to infectious diseases including whooping cough (pertussis), and they’re too young to get vaccinated. But they can be protected if their mothers received certain vaccines during pregnancy. Whooping cough is extremely contagious, outbreaks are continuing, and newborns are at the highest risk for severe pertussis infections. So since 2012, the Advisory Committee on Immunization Practices has recommended Tdap (tetanus, diphtheria, and acellular pertussis) vaccine for all pregnant women, preferably between 27 and 36 weeks’ gestation, even if they’ve already gotten the vaccine earlier. The American College of Obstetricians and Gynecologists has also endorsed this recommendation.

As with so many trends, California led the way

In 2010, California was the first to recommend Tdap vaccine for pregnant women. The reason: A whooping cough outbreak there claimed newborn babies’ lives. Getting the flu vaccine during pregnancy has been shown to be safe for women and their babies, but not much was known about the safety of Tdap vaccine in that setting.

That’s why Vaccine Safety Datalink (VSD) scientists including Michael L. Jackson, PhD, an assistant investigator at Group Health Research Institute, compared how common various health problems are for those pregnant women who did—or didn’t—receive Tdap vaccine, and for their babies. They studied more than 123,000 women at two sites: Kaiser Permanente Northern and Southern California.

Receiving Tdap vaccine during pregnancy wasn’t linked to increased risks for adverse birth outcomes (preterm birth or low birthweight for gestational age) or for hypertensive disorders of pregnancy (gestational hypertension, pre-eclampsia, or eclampsia). That’s what they published in “Evaluation of the association of maternal pertussis vaccination with obstetric events and birth outcomes” in the November 12, 2014 JAMA.

One raised risk for mother’s health

The study found a small increased risk for being diagnosed with chorioamnionitis, which is an inflammation of the fetal membranes (the amnion and chorion) caused by bacterial infection.

“But that result should be interpreted with caution,” Dr. Jackson said, “because the magnitude of this risk was small, and we found no increased risk for preterm birth, which is normally a major result of chorioamnionitis.”

The Centers for Disease Control and Prevention (CDC) funded this study.

Dr. Jackson’s coauthors are at the CDC; HealthPartners Institute for Education and Research in Minneapolis; Yale University in New Haven; Harvard Medical School and Harvard Pilgrim Health Care Institute in Boston; Kaiser Permanente of Northern California in Oakland; Kaiser Permanente Southern California in Pasadena; Kaiser Permanente Northwest in Portland, OR; Kaiser Permanente Georgia in Atlanta; and Kaiser Permanente Colorado in Denver.

Vaccine Safety Datalink

The VSD is a collaborative effort between the CDC’s Immunization Safety Office and nine large integrated health care organizations in the HMO Research Network, including Group Health. The VSD is recognized as the primary mechanism for population-based evaluations of vaccine safety in the United States. The VSD’s objectives are to conduct population-based research on immunization safety questions; evaluate immunization safety hypotheses that arise from medical literature, passive surveillance systems, adjustments to immunization schedules, and introduction of new vaccines; guide national immunization policy decisions; and partner with healthcare providers, public health officials, and others to ensure the public has the best available information regarding the risks and benefits of immunization.

About Kaiser Permanente

Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America’s leading health care providers and not-for-profit health plans. Founded in 1945, Kaiser Permanente has a mission to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve more than 12.4 million members in eight states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal Permanente Medical Group physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health. For more information, go to:


Media contact

For more on Kaiser Permanente Washington Health Research Institute news, please contact:

Amelia Apfel

(425) 507-5455
After-hours media line: (206) 287-2055

page-twitter-icon.png @KPWaResearch