What is the Influenza Virus?
Influenza, or commonly called the flu, is a highly contagious respiratory illness caused by a virus. It spreads easily through coughs, sneezes, or by touching contaminated surfaces. Some people can spread the virus even if they don’t feel sick; this is called asymptomatic transmission. Flu symptoms can include fever, chills, fatigue, sore throat, and body aches.1
While it’s often mild, the flu can lead to serious complications, like pneumonia, especially in vulnerable groups like young children, older adults, pregnant individuals, and those with pre-existing chronic health conditions such as asthma, diabetes, and cardiovascular disease. 1 There are two main types of viruses that cause the flu: influenza A and B. While both share many similarities, type A is responsible for most cases and is generally associated with more severe illness than type B.2
Vaccine Development and Annual Updates
The first inactivated flu vaccine (i.e., containing “killed” viruses that cannot cause sickness) was developed in the early 1940s. It was initially tested on military personnel to ensure it was safe and effective, and later approved for broader public use in 1945.1
Influenza viruses mutate rapidly, changing their structure over time and giving rise to many different strains of the virus. These ongoing changes mean that last year’s vaccine may not fully protect you against this year’s virus. As a result, the World Health Organization (WHO) monitors flu strains around the world and recommends which ones to include in the seasonal flu vaccine each year. In other words, scientists must update the flu vaccine annually to match the most common strains expected to spread during the upcoming flu season.1
The seasonal flu is estimated to kill up to 650,000 people globally each year. Getting vaccinated each year is the most effective way to protect individuals and the community from influenza and its severe complications that may lead to hospitalization and death.3,4
Note: Influenza vaccination during pregnancy protects both mother and baby by reducing flu-related risks and transferring antibodies to the infant.12
Why the Flu Vaccine Matters for Pregnant Individuals
The WHO currently lists pregnant individuals as a top priority group for receiving inactivated seasonal influenza vaccines due to their increased risk. In past influenza pandemics, such as those in 1918 and 1957, death rates among pregnant individuals were significantly higher than in the general population.5 Pregnant individuals face higher risks of pneumonia, hospitalization, ICU admission, and death from influenza. These risks are most pronounced in the third trimester.6
Pregnancy causes changes in the immune system, cardiovascular function, and respiratory capacity, all of which can make it harder for the body to respond effectively to respiratory infections like the flu.7
Influenza during pregnancy also increases risks to the fetus, including miscarriage, neural tube defects (birth defects of the brain or spinal cord, especially if infected in the first trimester), low birth weight, premature delivery, and stillbirth.8,9,10
Benefits of the Influenza Vaccine
Vaccination significantly reduces the risk of influenza-related illness and hospitalization in both the pregnant mother and the baby. For the mother, the vaccine reduces flu risk by approximately 40 to 60%, depending on the season and strain.3
When a pregnant mother gets the flu shot, her body creates antibodies, which are special proteins made by the immune system to help fight off the virus. Some of these antibodies pass from the mother to the baby through the placenta before birth, offering protection to infants during their first six months.11 This early protection is very important because babies under six months are too young to receive the flu vaccine, and their immune systems are still developing, making them more likely to become seriously ill if they catch the flu.11 Studies conducted in Ontario show that maternal vaccination was associated with a 64% reduction in flu-related hospitalization in infants under six months old.11
Is It Safe?
Yes, the vaccine can be given safely at any stage of pregnancy. Inactivated influenza vaccines are not associated with miscarriage, birth defects, or preterm birth.13,14 However, live-attenuated influenza vaccines, which contain weakened but live viruses, are not recommended for use during pregnancy.15
Gaps and Disparities in Vaccine Uptake
Despite clear benefits, not all pregnant individuals receive the flu vaccine. Barriers such as healthcare access, transportation, systemic racism, language barriers, and mistrust of the healthcare system contribute to lower vaccination rates, especially among racialized communities, rural or remote regions, and those with lower socioeconomic status (often younger pregnant women).16
Surveys also show that hesitancy is common. Among those who chose not to vaccinate, reasons included concerns about vaccine efficacy and safety during pregnancy, lack of awareness, personal hesitancy, or low perceived risk.17 In a 2022 study, Regan & Fiddian-Green found that one survey in China indicated awareness of vaccine recommendations was as low as 15% among pregnant patients.17
Recent Vaccination Trends in Canada
In Canada, flu vaccine uptake among pregnant women rose from 45% in 2019 to 53% in 2021, but coverage still varies across provinces.18 For instance, British Columbia reported a 61% uptake, while Quebec was significantly lower at 44.2%.18 One of the strongest predictors of vaccine uptake is provider recommendation. In 2023–2024, about 70% of Canadian women who received a strong recommendation from a healthcare professional chose to get vaccinated, compared to just 37% of women who chose to get vaccinated without encouragement from a provider.19
Conclusion
Pregnancy is a time of great care, and the flu vaccine is one of the simplest, most effective ways to safeguard both maternal and infant health. By choosing to get vaccinated, pregnant individuals can protect themselves from serious complications and pass on vital early immunity to their babies. As evidence continues to show the vaccine’s safety and impact, improving awareness, access, and trust in flu vaccination remains a meaningful public health priority that supports healthier beginnings for families across Canada.
References
- 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.
- 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.
- 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
- 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.
- 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
- 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.
- 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.
- 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
- 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
- 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.
- 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
- 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
- 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.
- 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
- 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.
- 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.
- 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
- 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.
- 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.