Seasonal influenza vaccine (‘flu jab’)

(Date: June 2014. Version: 2)

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by Public Health England on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.

What is it?

Seasonal influenza vaccines contain inactivated forms of certain flu viruses that stimulate the body to develop immunity to the flu strains in the vaccine. The seasonal influenza vaccine is changed each year to protect against the types of flu that are expected to be most common in the coming flu season (usually winter). Since 2009, most seasonal flu vaccines have included the ‘swine flu’ virus. A lot of very useful information on the effects of swine flu vaccines was collected from pregnant women all around the world during the 2009-2010 swine flu pandemic.

Why is it advised that I receive the seasonal influenza vaccination during pregnancy?

Due to the changes that normally occur during pregnancy, pregnant women are more likely to become seriously ill if they catch flu, especially if they are more than 24 weeks pregnant, or have an underlying health condition such as asthma, diabetes or obesity. Some studies have also shown that flu infection in pregnancy increases the chance of miscarriage or stillbirth. For these reasons it is recommended that all pregnant women in the UK are vaccinated against influenza.

Receiving the seasonal influenza vaccine during pregnancy is also thought to protect the baby after birth. When a pregnant woman receives the flu vaccine she produces antibodies (molecules that fight infections) that can cross the placenta to her unborn baby. These antibodies have been shown to remain in the baby for a few months after birth and may help to protect the baby from being infected with flu in the first few weeks of life.

Do I still need the vaccination if I have had flu, or had a flu jab last year?

The types of flu virus that circulate in the population change all the time, and the seasonal influenza vaccine therefore also usually changes every year. This means that the previous year’s vaccine, or indeed a previous flu infection, may not provide any protection against the current type of flu. Additionally, many people who think that they have had flu may have just had a heavy cold and will therefore not be naturally protected from catching flu. It is therefore advised that all pregnant women, regardless of their past history of flu infection or vaccination, receive the seasonal influenza vaccine.

Can the seasonal influenza vaccine cause birth defects in my baby?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects.

There is no evidence from any of five studies that women who were vaccinated with seasonal influenza vaccine during the first trimester were at increased risk of having a baby with a birth defect.

A further sixteen studies investigated a total of over 10,000 pregnant women who received a swine flu vaccination during the 2009-2010 pandemic. None of these studies showed that women who were vaccinated during the first trimester were more likely to have a baby with a birth defect. 

Can the seasonal influenza vaccine cause miscarriage?

There is no evidence from any of the four studies that investigated miscarriage that pregnant women who are vaccinated with seasonal influenza vaccine are at increased risk.

A further six studies have also not shown any link between swine flu vaccination during pregnancy and miscarriage.

Can the seasonal influenza vaccine cause stillbirth?

None of the four studies that looked at stillbirth showed any increased risk in pregnant women who were vaccinated with seasonal influenza vaccine. In fact, one of these studies found that women who were vaccinated against influenza during pregnancy had a lower risk of stillbirth. As these results were from just one study, more research is required to confirm this finding.

Seven studies which focused specifically on swine flu vaccination during pregnancy also showed no link between stillbirth and being vaccinated.

Can the seasonal influenza vaccine cause preterm birth, or my baby to be small at birth (low birth weight)?

Several studies have been carried out and none have shown any links between seasonal influenza vaccination during pregnancy and an increased risk of preterm birth (before 37 weeks of pregnancy), or of having a low birth weight baby (<2500g).

Some studies have shown that being vaccinated against flu during pregnancy, particularly during periods when levels of flu infection in the population are high, can protect against preterm birth and/or having a low birth weight baby.

Can the seasonal influenza vaccine cause learning or behavioural problems in the child?

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

There is no known link between having an influenza vaccination whilst pregnant and learning or behavioural problems (such as ADHD or autism spectrum disorder) in the child. There are, however, no scientific studies that have specifically investigated a link with these problems.

Will my baby need extra monitoring during pregnancy?

Being vaccinated against influenza during pregnancy is not expected to cause any problems that would require extra monitoring of your baby.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from  

General information 

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks.  They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby.  There are, however, some medicines that can harm a baby’s normal development.  How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.   

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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