The Upshot Series #8

Understanding vaccination in pregnancy

Published on: July 5, 2021


In this eighth installment of Sanofi’s Upshot series on vaccines, we invited guest author, Liana Clark, Global Medical Product Lead for Polio, Pertussis and Hib (PPH) Vaccines for Sanofi Pasteur, to share her expertise and experience on vaccination in pregnancy. Prior to joining Sanofi, Liana was an Assistant Professor of Pediatrics at the University of Pennsylvania School of Medicine and an attending physician at The Children’s Hospital of Philadelphia. She is also a professional photographer whose work is featured in this story. 

In the early days of COVID-19 vaccination, there was much discussion about whether the new vaccines should be used in pregnancy, as they had not specifically been tested in pregnant women. Was the potential benefit worth the potential unknown risks?

Traditionally, a new vaccine against any infectious disease is assessed in clinical trials prior to use, but these trials don’t normally include pregnant women. When considering the need for vaccination during pregnancy, public health officials assess the risk of the disease to the mother-to-be and/or her infant at birth by looking at the type of vaccine technology used, i.e., usually using a live or inactivated virus; how the vaccine works; and the safety profile. If the health benefits outweigh the potential risks, the health authorities make recommendations for vaccination in pregnancy.1

How vaccines are assessed for use in pregnant women

Let’s take influenza as an example: When women are pregnant, their immune systems and several vital organs adapt to carrying the fetus.2 The changes put the pregnant woman at increased risk of severe influenza,3 as she is less able to fight off the high fevers and inflammation caused by the disease. One study estimated that pregnant women were seven times more likely to end up in hospital from influenza than non-pregnant women.4 These high risks drive healthcare providers and the World Health Organization to routinely recommend influenza vaccination in pregnancy.5

There’s another example in Tdap (tetanus, diphtheria, and pertussis booster) vaccination in pregnancy.  Here, much of the focus is on preventing severe pertussis disease in newborns and infants too young to be vaccinated. Unlike influenza, pertussis is not seasonal but can circulate year round, and can worsen during outbreaks. It is highly contagious, and many infants catch it from family members, before they’ve even ventured outside.6 The result: 80% of pertussis-related deaths occur in infants younger than three months old.7

How vaccination against pertussis works during pregnancy to help protect the newborn

How vaccination against pertussis works during pregnancy to help protect the newborn

When the pregnant woman is vaccinated, her body creates antibodies that are passed to the fetus. These antibodies are present in the newborn at birth and last between two and four months.9 Studies have shown that Tdap vaccination in pregnancy reduces the risk of pertussis infection by approximately 90% in a newborn’s first two months of life and reduces pertussis-related deaths by 95% in infants of vaccinated mothers.10

During my years in pediatrics, I saw too many young infants in the intensive care unit struggling to breathe due to pertussis. This is something that stays with you.
Liana Clark

Liana Clark

Global Medical Product Lead PPH, Sanofi Pasteur

While vaccination in pregnancy has become routine, some pregnant women still hesitate. It is important for these women to know that influenza and Tdap vaccines have been routinely used during pregnancy for more than a decade in countries worldwide. The safety profile has been favorable with studies showing no serious vaccine-related side effects for the pregnancy or in the infant.

With respect to COVID-19, public health authorities noted the good safety profiles of licensed vaccines in clinical trials among the general population and felt it unlikely that the safety profile would be different in pregnant women; especially given that the risk of harm from COVID-19 in pregnant women was too great not to vaccinate them. That’s why the authorities now provide unanimously favorable recommendations for COVID-19 vaccination in pregnant women. 

Liana Clark, Global Medical Product Lead for PPH Vaccines for Sanofi Pasteur, and her daughter Zara

As a pediatrician and an epidemiologist, I am a passionate advocate for vaccines. Vaccines save lives, and vaccination in pregnancy is a critical intervention that provides protection to both pregnant women and their infants. My baby was born before most pregnancy vaccination recommendations were put in place, but as a mother and future grandmother, I hope that I will be the one driving my pregnant daughter to her vaccination appointments to ensure that both she and her baby are protected from the risks of infectious diseases.


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  1. Mackin DW, Walker SP. The Historical Aspects of Vaccination in Pregnancy. Best Practice & Research Clinical Obstetrics & gynaecology. 2020:S1521-6934(1520)30158-30159. [Last accessed: June 2021]
  2. Tan EK, Tan EL. Alterations in Physiology and Anatomy During Pregnancy. Best Practice & Research Clinical Obstetrics & Gynaecology. 2013;27:791-802. [Last accessed: June 2021]
  3. CDC. Flu & Pregnant Women  [Last accessed: June 2021]
  4. BMC. Pregnancy as a risk factor for severe influenza infection: an individual participant data meta-analysis [Last accessed: June 2021]
  5. WHO report. Influenza epidemiology and immunization during pregnancy: Final report of a World Health Organization working group. [Last accessed: June 2021]
  6. CDC. Pertussis, Causes and Transmission  [Last accessed: June 2021],where%20you%20share%20breathing%20space
  7. CDC. Pertussis. In: Hamborsky J, et al, edseds. Epidemiology and Prevention of Vaccine Vaccine-Preventable Diseases . 13th ed . Washington, DC: Public Health Foundation ; 2015 
  8. Winter K, Nickell S, Powell M, Harriman K. Effectiveness of Prenatal Versus Postpartum Tetanus, Diphtheria, and Acellular Pertussis Vaccination in Preventing Infant Pertussis. Clin Infect Dis. 2017;64(1):3-8.
  9. Gall SA, Myers J, Pichichero M. Maternal immunization with tetanus, diphtheria, pertussis vaccine: effect on maternal and neonatal serum antibody levels. Am J Obstet Gynecol. 2011;204(4):334.e331-335.
  10. Amirthalingam G, Campbell H, Ribeiro S et al. Sustained effectiveness of the maternal pertussis immunization program in EnglandEngland3 years following introduction. Clin Infect Dis. 2016;63(S4):S236 S236–S243. 
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