What is the Influenza Virus? 

Flu Vaccination During Pregnancy Protects You and Your Baby-Centre for New Immigrant Well-Being (CNIW)

Influenza, also called the flu, is a very contagious illness that affects your lungs and breathing. It spreads easily through coughing, sneezing, or touching things that have the virus on them and then touching your face. Some people can spread the flu even if they don’t feel sick. This is called asymptomatic transmission. Flu symptoms often include fever, chills, feeling very tired, sore throat, cough, headache, and body aches.1 

Even though the flu is usually mild, it can sometimes lead to serious problems, like pneumonia, an infection of the lungs that makes breathing difficult. Serious illness is more common in people who have higher risk, such as young children under age five, adults over age 65, pregnant people, and people with existing health issues like asthma, diabetes, or heart disease.1 There are two main types of viruses that cause flu illness: influenza A and B. Both are similar, but influenza type A causes most cases each year and usually causes more serious illness than type B.2

History of the Flu Vaccine

The first flu vaccine that used “killed” viruses (meaning the viruses are no longer alive and can't make you sick) was developed in the early 1940s. At first, the vaccine was tested on soldiers to make sure it was safe and worked well. In 1945, it was approved for everyone else to use.1

Flu viruses change quickly, forming new versions or "strains" all the time. Because of these constant changes, the flu shot you received last year might not protect you against this year's virus. That’s why groups like the World Health Organization (WHO) closely watch flu viruses all around the world. They study which types are spreading and recommend which ones to include in each year’s flu vaccine. This means scientists need to update the vaccine every year to match the flu viruses most likely to spread during the upcoming flu season.1

Each year, the flu causes up to 650,000 deaths worldwide. Getting the flu shot every year is the best way to protect yourself, your family, and your community from the flu and serious problems it can cause, including hospital stays or death.3,4

Why the Flu Vaccine Matters for Pregnant Individuals

The WHO says pregnant people are among the first who should get the flu vaccine because they have higher risks. During past flu outbreaks, such as the ones in 1918 and 1957, more pregnant people died from flu compared to other groups.5 Pregnant people are also more likely to develop pneumonia, be hospitalized, need intensive care, or even die if they catch the flu. These risks become even greater later in pregnancy, especially after 28 weeks (third trimester).6

Pregnancy causes many changes in a person's body, including the immune system, heart, and lungs. These changes can make it harder to fight off infections.7 Catching the flu while pregnant can also harm the developing baby. Possible problems include miscarriage (losing the baby), birth defects affecting the baby's brain or spine, low birth weight, being born too early, or stillbirth (the baby dying before birth).8,9,10

Benefits of the Influenza Vaccine

Getting the flu shot greatly reduces the risk of getting sick or needing hospital care from the flu for both the pregnant person and their baby. For the pregnant person, the flu shot can lower the chance of getting the flu by about 40% to 60%, depending on the season and the types of flu viruses circulating.3

When a pregnant person gets the flu vaccine, their body creates special proteins called antibodies that help fight viruses and prevent illness. These antibodies travel from the mother to the baby through the placenta (the organ connecting mother and baby) before birth, providing the baby protection for their first six months of life.11 This early protection matters because babies younger than six months cannot receive the flu vaccine, and their immune systems are not fully developed. This means that babies have a weaker ability to fight infections, so they are at greater risk of becoming seriously ill from the flu.11 Research from Ontario found that babies whose mothers got vaccinated during pregnancy had a 64% lower chance of being hospitalized from the flu in their first six months.11

Flu Vaccination During Pregnancy Protects You and Your Baby-Centre for New Immigrant Well-Being (CNIW)

Figure 1. Influenza vaccination during pregnancy protects both mother and baby by lowering flu-related risks and passing on protective antibodies to the baby.12

Is It Safe?

Yes. The flu vaccine can be given safely at any stage of pregnancy. Studies show clearly that "inactivated" flu vaccines (those with killed viruses) are safe during pregnancy and do not cause miscarriage, birth defects, or early birth.13,14 However, another kind of vaccine called "live-attenuated" vaccines, which contain live but weakened flu viruses, are not recommended for pregnant people.15

Gaps and Disparities in Vaccine Uptake

Even though getting the flu shot during pregnancy has clear health benefits, not all pregnant people get vaccinated. Many factors can stop someone from getting a flu vaccine. These factors include difficulty accessing health care, transportation problems, racism in the healthcare system, language barriers, and mistrust of doctors or healthcare providers. These barriers are especially common for racialized communities, people living in rural or remote places, or people with lower incomes (who are often younger pregnant individuals).16

Surveys also show that some pregnant people feel unsure or hesitant about getting the flu vaccine. Reasons include worrying whether the vaccine is safe or effective during pregnancy, not knowing that doctors recommend it, or thinking that the flu isn't a big risk.17 In 2022, researchers Regan and Fiddian-Green reported that a survey from China showed only 15% of pregnant people knew the flu shot was recommended during pregnancy.17

Recent Vaccination Trends in Canada

In Canada, more pregnant people are now choosing to get the flu vaccine. Flu vaccine rates increased from 45% in 2019 to 53% in 2021, but vaccination rates still vary depending on which province you live in.18 For example, in British Columbia, 61% of pregnant people got the vaccine, while in Quebec, the rate was much lower at 44.2%.18 One important factor that helps pregnant people decide to get vaccinated is when their healthcare provider recommends it. In 2023-2024, about 70% of pregnant people who received a clear, strong recommendation from their doctor or nurse got vaccinated, compared to only 37% who chose to get vaccinated without this recommendation.19

Conclusion

Pregnancy is an important time for extra care and protection. Getting the flu shot during pregnancy is one of the simplest and most effective ways to protect both the pregnant person and their baby. Vaccination lowers the risk of severe flu illness during pregnancy and provides important early protection for babies. As ongoing research continues to clearly show that the flu vaccine is safe and effective, improving people's awareness about the flu vaccine, making it easier to get, and building trust in vaccination remain important public health goals. These goals help ensure healthier starts for families across Canada.

References

  1. World Health Organization. (2025). History of influenza vaccination. https://www.who.int/news-room/spotlight/history-of-vaccination/history-of-influenza-vaccination. Accessed June 10, 2025.
  1. Cleveland Clinic. (2025). What’s the Difference Between Influenza A and Influenza B? https://health.clevelandclinic.org/flu-a-vs-flu-b. Accessed June 10, 2025.
  1. Trombetta, C. M., Kistner, O., Montomoli, E., Viviani, S. and Marchi, S. (2022). Influenza Viruses and Vaccines: The Role of Vaccine Effectiveness Studies for Evaluation of the Benefits of Influenza Vaccines. Vaccines (Basel). 10, 714. doi: 10.3390/vaccines10050714
  1. Public Health Agency of Canada. (2025). Influenza vaccines: Canadian Immunization Guide. https://www.canada.ca/en/public-health/services/publications/healthy-living/canadian-immunization-guide-part-4-active-vaccines/page-10-influenza-vaccine.html. Accessed June 10, 2025.
  1. Sakala, I. G., Honda-Okubo, Y., Fung, J. and Petrovsky, N. (2016). Influenza immunization during pregnancy: Benefits for mother and infant. Hum Vaccin Immunother. 12, 3065–3071. doi: 10.1080/21645515.2016.1215392
  1. Public Health Agency of Canada. (2023). Updated guidance on influenza vaccination during pregnancy. https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/national-advisory-committee-immunization-updated-guidance-influenza-vaccination-during-pregnancy.html. Accessed June 10, 2025.
  1. Centers for Disease Control and Prevention. (2025). Respiratory Viruses and Pregnancy. https://www.cdc.gov/respiratory-viruses/risk-factors/pregnancy.html. Accessed June 10, 2025.
  1. Wang, R., Yan, W., Du, M., Tao, L. and Liu, J. (2021). The effect of influenza virus infection on pregnancy outcomes: A systematic review and meta-analysis of cohort studies. Int J Infect Dis. 105, 567–578. doi: 10.1016/j.ijid.2021.02.095
  1. Mátrai, Á., Teutsch, B., Váradi, A., Hegyi, P., Pethő, B., Fujisawa, A., et al. (2022). First-Trimester Influenza Infection Increases the Odds of Non-Chromosomal Birth Defects: A Systematic Review and Meta-Analysis. Viruses. 14, 2708. doi: 10.3390/v14122708
  1. Centers for Disease Control and Prevention. (2020). New Study Finds Influenza during Pregnancy is Associated with Increased Risk of Pregnancy Loss and Reduced Birthweight. https://www.cdc.gov/flu/spotlights/2020-2021/influenza-pregnancy-loss.htm. Accessed June 10, 2025.
  1. Fell, D. B., Russell, M., Fung, S. G., Swayze, S., Chung, H., Buchan, S. A., et al. (2024). Effectiveness of Influenza Vaccination During Pregnancy Against Laboratory-Confirmed Seasonal Influenza Among Infants Under 6 Months of Age in Ontario, Canada. J Infect Dis. 230, e80–e92. doi: 10.1093/infdis/jiad539
  1. Buchy, P., Badur, S., Kassianos, G., Preiss, S. and Tam, J. S. (2020). Vaccinating pregnant women against influenza needs to be a priority for all countries: An expert commentary. Int J Infect Dis. 92, 1–12. doi: 10.1016/j.ijid.2019.12.019
  1. Centers for Disease Control and Prevention. (2024). Flu Vaccine Safety and Pregnancy. https://www.cdc.gov/flu/vaccine-safety/vaccine-pregnant.html. Accessed June 10, 2025.
  1. Giles, M. L., Krishnaswamy, S., Macartney, K. and Cheng, A. (2018). The safety of inactivated influenza vaccines in pregnancy for birth outcomes: a systematic review. Hum Vaccin Immunother. 15, 687–699. doi: 10.1080/21645515.2018.1540807
  1. Public Health Agency of Canada. (2025). Immunization in pregnancy and breastfeeding: Canadian Immunization Guide. https://www.canada.ca/en/public-health/services/publications/healthy-living/canadian-immunization-guide-part-3-vaccination-specific-populations/page-4-immunization-pregnancy-breastfeeding.html. Accessed June 10, 2025.
  1. Public Health Agency of Canada. (2024). Full report: Realizing the Future of Vaccination for Public Health. https://www.canada.ca/en/public-health/corporate/publications/chief-public-health-officer-reports-state-public-health-canada/state-public-health-canada-2024/report.html. Accessed June 10, 2025.
  1. Regan, A. K. and Fiddian-Green, A. (2022). Protecting pregnant people & infants against influenza: A landscape review of influenza vaccine hesitancy during pregnancy and strategies for vaccine promotion. Hum Vaccin Immunother. 18, 2156229. doi: 10.1080/21645515.2022.2156229
  1. Public Health Agency of Canada. (2022). Results of the Survey on Vaccination during Pregnancy 2021. https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/survey-vaccination-during-pregnancy-2021.html. Accessed June 10, 2025.
  1. Public Health Agency of Canada. (2025). Seasonal Influenza Vaccination Coverage in Canada, 2023-2024. https://www.canada.ca/en/public-health/services/immunization-vaccines/vaccination-coverage/seasonal-influenza-survey-results-2023-2024/full-report.html. Accessed June 10, 2025.

By: Lisa Fang