Seasonal influenza vaccine (‘flu jab’)

(Date: November 2017. Version: 3)

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 flu virus particles that stimulate the body to produce antibodies (molecules in the immune system that fight infections) specific to the flu strains in the vaccine. The seasonal influenza vaccine is changed each year to match the types of flu that are predicted to be most common in the coming winter flu season. Since 2009 most seasonal flu vaccines have included the ‘swine flu’ virus (sometimes called H1N1).

Why is it advised that I receive the 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 the latter half of pregnancy is also thought to protect the baby after birth. When a pregnant woman receives the flu vaccine she produces antibodies that can cross the placenta to her unborn baby. These antibodies have been shown to remain in the baby 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 influenza vaccination if I have had flu infection or the 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 flu infection or having the flu vaccine in a previous year 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 in this instance will 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 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 studies of over 72,000 women who received influenza vaccines during the first trimester that vaccination is linked to birth defects in the baby.

Can the influenza vaccine cause miscarriage?

Five well designed studies have investigated the occurrence of miscarriage in pregnant women who were vaccinated against influenza.

Four studies provide no evidence of any link between influenza vaccination and miscarriage. The fifth study found that miscarriage was more common following influenza vaccination in pregnancy in woman who had also received a swine flu-containing vaccine in the previous flu season. It is unclear whether the higher chance of miscarriage seen in this study is linked to repeated vaccination, or whether women who are vaccinated in successive flu seasons are more likely to have an underlying illness which in itself increases the risk of miscarriage. Further studies of women receiving regular flu vaccines are required before any conclusions regarding miscarriage risk can be drawn.

Can the seasonal influenza vaccine cause stillbirth?

Studies of over 265,000 pregnant women receiving influenza vaccines have not shown any increase in stillbirth compared to unvaccinated women. Although some of these studies suggest that influenza vaccination in pregnancy may reduce the occurrence of stillbirth, more studies are needed to confirm this observation. 

Can the influenza vaccine cause preterm birth?

Several studies, which together include over 206,000 pregnant women receiving influenza vaccines during pregnancy, do not suggest a link with preterm birth (<37 weeks). Some of these studies suggest that influenza vaccination in pregnancy might reduce the likelihood of preterm birth, however further studies are needed to assess whether this the case, and if so whether this only applies to certain women, for example, those who have an underlying health condition associated with early delivery.

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

Several studies, which together include over 207,000 pregnant women vaccinated against influenza during pregnancy, do not suggest a link with poor growth of a baby in the womb. Some of these studies suggest that influenza vaccination in pregnancy might possibly reduce the likelihood of a baby being smaller than average at delivery, however further studies are needed to assess whether this is the case or whether the underlying health of the mother is influencing these findings.

Can the 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.

A study of over 45,000 children aged between two and 15 years who had been exposed in the womb to flu vaccines found that they were no more likely to be diagnosed with an autism spectrum disorder than children of women who did not have a flu vaccine during pregnancy.

Another study of around 1,200 babies under the age of one year who had been exposed in the womb to flu vaccines found no difference in development compared to babies who were not exposed to flu vaccines before birth.

These studies offer some reassurance, although ideally further research to confirm these individual study findings is required.

Are there any risks to my baby if the father has received a flu vaccine?

There are no scientific reports of babies born to men who received a flu vaccination around the time of conception. Most experts agree that the majority of medicines used by the father are unlikely to harm the baby through effects on the sperm. However, more research on the effects medicine use in men around the time of conception generally is needed.

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

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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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