The Facts about Flu Vax and Pregnancy

Influenza (flu) is a highly contagious respiratory viral infection that circulates each year in the winter months and can cause serious illness in previously healthy people.

Unlike a cold, flu symptoms develop abruptly one to three days after infection, and can include: tiredness, high fever, chills, headache, sore throat, coughing, sneezing, runny noses, poor appetite, and muscle aches. Most people who get the flu will suffer from mild illness and recover in around four weeks. In some cases, severe illness and complications such as pneumonia can develop, which can result in hospitalisation and even death. Even if you are generally healthy and rarely get sick, changes in immune, heart & lung functions during pregnancy make you more likely to become seriously ill.

The immune system is one of the most important systems protecting the mother against the environment and preventing damage to her unborn baby. Immune responses are thought to be weakened in pregnancy to keep the body from rejecting the fetus, hence making pregnant women more susceptible to coughs, colds and flu. However, immune cells at the implantation site (placenta) are not suppressed, rather are active and carefully controlled, protecting the fetus from infection. It is now understood influenza in pregnancy is a hyperinflammatory disease rather than a state of immunodeficiency (Kay et al, 2014). Therefore, when pregnant women contract influenza, they tend to get very unwell due to the unique modulated immune response to ‘over-react to the flu’.

The Australian Government and Royal Australian and New Zealand College of Obstetricians and Gynaecologists recommend that all pregnant women be offered vaccination against flu:

To protect themselves – Complications such as pneumonia are more common, with reports pregnant women are 5 times more likely to be admitted to ICU than other women who contract influenza. Additionally, influenza causes a 4 times greater likelihood of premature birth, again thought to be a result of interference with the maternal inflammatory pathway that is normally activated later in pregnancy to prepare the body for birth.

To protect their baby – After immunisation, your body produces antibodies that are passed to your unborn baby and help protect him/her up to 6 months after the birth. Babies born to mothers who have been immunisated are 25% less likely to be hospitalized themselves for flu-related illness. This is important because babies younger than 6 months are too young to get vaccinated against the flu. If you breastfeed, antibodies made in response to your influenza vaccination may also be passed in breast milk providing additional protection to your newborn

Annual vaccination is therefore the best way of preventing the flu and any associated illness. The risk-benefit of vaccination during all stages of pregnancy has been carefully evaluated. The The flu vaccine is redefined each year as protection is limited to those strains of virus from which the vaccine is prepared or closely related strains.
The World Health Organization (WHO) recommends pregnant women should receive the highest priority for the influenza vaccination. For 2018 the WHO recommends a composition of the trivalent influenza vaccine (TIV) for the southern hemisphere winter 2018 influenza season as:

• an A/Michigan/45/2015 (H1N1)pdm09 like virus;
• an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus; and
• a B/Phuket/3073/2013-like virus (Yamagata lineage)

Quadrivalent influenza vaccines (QIV) containing two influenza B viruses should include the above three viruses and a B/Brisbane/60/2008-like virus (Victoria lineage).
For best protection against the flu, Queensland Health recommends women should be vaccinated as soon as possible in the flu season and has funded this for pregnant women under the state and national influenza programs. Flu vaccination is safe to be given at any time during pregnancy, as well as given at the same time as the pertussis “whooping cough” vaccination (28-32wks). The flu vaccine provides effective protection (70-90% effectiveness overall) and is available from your GP or immunization provider.
For further information, see list below:

• Queensland Health: https://www.health.qld.gov.au/clinical-practice/guidelines-procedures/diseases-infection/immunisation/research

• Australian Government Immunise Australia website: http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/pregnant-women

• National Centre for Immunisation Research and Surveillance fact sheets: http://www.ncirs.edu.au/assets/provider_resources/fact-sheets/vaccinations-in-pregnancy-fact-sheet.pdf

References:
Mor, G & Cardenas, I. (2010). The Immune System in Pregnancy: A unique Complexity. American Journal of Reproductive Immunology, 63(6), 425-433. doi: 10.1111/j.1600-0897.2010.00836.x

Kay, A.W., Fukuyama, J., Aziz, N., Dekker, C.L., Mackey, S., Swan, G.E., Davis, M.M., Holmes, S. & Blish, C.A. (2014). Enhanced natural killer-cell and T-cell responses to influenza A virus during pregnancy. PNAS, 111(40), 14506-14511. doi:10.1073/pnas.1416569111