Should Pregnant Women Get the Flu Vaccine?
Kelsey McLaughlin, PhD
The Public Health Agency of Canada estimates that 10-20% of Canadians get the flu every year. Although most people who are sick with the flu will make a full recovery with few complications, pregnant women have a higher risk of more serious complications related to the flu and hospitalization than the general population.
However, many women have concerns about the flu vaccine and want to make sure the flu vaccine is a safe way to protect mom and baby from the flu and related complications.
What is the flu?
The flu is medically known as the influenza virus. There are four types of influenza viruses, with type A & B causing the classic flu that circulates in our communities every year.
These two types of influenza viruses are further divided into subcategories, depending on the protein markers on the outside of the virus. Influenza viruses are characterized by these specific protein markers; for example, H1N1 indicates that this strain of flu virus is an orthomyxovirus with haemagglutinin (H) and neuraminidase (N) protein markers.
Clinical course of the flu virus
The flu virus is a contagious respiratory illness, meaning that it impacts the systems involved with our breathing. Infection with the flu virus can cause a wide range of symptoms, from mild to severe illness. Typical symptoms of the flu include high fever, cough, muscle aches, headache, chills, fatigue and loss of appetite. When you first contract the flu, there is typically a period of a couple days where the virus is incubating and does not cause any noticeable symptoms.
This virus is transmitted through airborne droplet form or physical contact. The flu is primarily spread through infected people coughing and sneezing. Once the virus enters the body through the nose or mouth, the flu virus begins to make copies of itself in the cells in the lung surface (epithelial cells).
Pregnant women are at higher risk of flu-related illness
There are a number of personal and virus-specific factors that determine how sick a person will be from the flu. Personal factors include existing immunity to the influenza virus, sex, age and genetic variations.
Most people with the flu will recover within 7 – 10 days. However, some people are at higher risk of severe illness caused by the flu; this includes adults and children with chronic health conditions, adults over the age of 65, children below the age of 5 and Indigenous peoples.
Pregnant women are also at higher risk of suffering flu-related complications than non-pregnant women. During the 2009 H1N1 flu pandemic, pregnant women were over 4 times more likely to be hospitalized, compared to the general population. Pregnant women also had more admissions to the intensive care unit and death, and other influenza-related complications.
Data from the 2009 H1N1 pandemic also shows that influenza is associated with a higher risk of poor pregnancy outcomes, such as preterm birth, stillbirth and neonatal death.
The reasons for this increased risk are not exactly clear, however, are thought to involve changes to the pregnant woman's cardiovascular and respiratory systems. Some animal models suggest that the immune response of pregnant mice to the influenza virus is reduced, when compared to non-pregnant mice.
Despite this data and recommendations, only 49% of American women received the flu vaccine before or during pregnancy. Reasons for women not receiving vaccination included lack of coverage and concern regarding the effectiveness of the flu vaccine.
How can pregnant women protect themselves from the flu?
Pregnant women can get an annual flu vaccine to protect themselves and their growing baby against influenza. The flu vaccine introduces an inactivated (dead) virus to your immune system and allows your immune system to start building up defenses against this virus; these defenses are referred to as antibodies. These antibodies will then protect the body the next time you come into contact with the flu virus naturally.
Every year, scientists and doctors determine which types of flu virus is likely to be the most common and dangerous, then create a vaccine to protect against those specific types of flu viruses. Since the flu virus is always changing and adapting, it is important that the vaccine is kept up to date in order to protect as many people as possible. Here is an interesting read of how this process works.
Additional practices to avoid the flu virus include proper hand washing, covering your mouth and nose when coughing and sneezing practices, as well as keeping shared surfaces clean to avoid spreading the flu virus.
Benefits of flu vaccination in pregnant women
A recent study published by the journal Clinical Infectious Diseases evaluated how the flu vaccine impacted flu-related hospitalizations of 1,000 pregnant women in Canada, United States, Israel and Australia. It was found that the flu vaccine in pregnant women provided a 40% protection against hospitalization for flu-related illness.
Another benefit of vaccination is the protection that the mother passes to the baby. When the mother receives the flu vaccine and increases antibodies against the flu, these antibodies are also passed to the baby through the placenta, providing defenses against the flu for the growing fetus.
A study of 340 pregnant women determined that the flu shot reduced the risk of influenza and other respiratory illness in both the moms and the babies, when compared to pregnant women who did not receive a flu shot. A large study examined over 55,000 births in Ontario and determined that moms who get the flu shot are less likely to have lower birthweight babies, pre-term birth and fetal death. Additional studies have determined that flu immunization in pregnant women was associated with higher baby birthweight during the flu season, when compared to pregnant women who did not get the flu shot.
Reassuringly, research studies have found that the flu vaccine did not increase the risk of adverse pregnancy outcomes, including fetal death, stillbirth and spontaneous abortion, with flu vaccination in pregnancy (read more here & here).
The flu vaccine is safe for pregnant women
A CDC-funded study published in 2017 reported an increased risk of miscarriage in the 28 days following vaccination in the 2010-2012 flu seasons. Since these findings were alarming, scientists repeated the study to include 3x more women, spanning the 2012-2015 flu seasons, and found no link between the flu shot and miscarriages. The results from the first study were thought to be due to statistical flukes that can occur in studies with small sample sizes. The CDC recommends that pregnant women get a flu vaccine during any trimester of their pregnancy.
In recent years, there has been public discussion and debate regarding the safety of pregnant women receiving the flu shot, relating to how the vaccine impacts both mom and baby’s health, especially relating to the development of autism in the baby. However, recent data determined that there is no association between mother’s receiving the flu vaccine during pregnancy and increased risk of autism spectrum disorders in the baby.
Guideline recommendations for pregnant women
The Society of Obstetricians and Gynaecologists of Canada states that the seasonal flu vaccine is safe and therefore recommended for all pregnant women. The SOGC recognizes that the flu vaccine will also help protect the baby in the first few months of life.
Similarly, The American College of Obstetricians and Gynecologists recommends that that women who are or will be pregnant during influenza season receive the flu vaccine as soon as it is available. ACOG states that inactivated influenza vaccines can be given safely during any trimester. Caution is recommended for women who have relevant allergies to the components of the vaccine.
Pregnant women are at higher risk of flu-related complications than the general population, and the flu can impact pregnancy outcomes. It is recommended that pregnant women get the flu shot to protect themselves and their babies.
Every woman and every pregnancy is unique. Pregnant women should speak to their healthcare provider to ensure maternal and fetal safety. This article is meant to provide readers with current information and opinions. All medical and treatment decisions should be discussed with your healthcare provider.