Yellow fever vaccine

(Date of issue: August 2015. 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?

Yellow fever vaccine (Stamaril®) is given by injection to reduce the risk of a person catching yellow fever. Yellow fever is a viral infection that is spread by mosquito bites and can cause serious illness. Almost 1 in every 10 people who catch yellow fever die from the illness. Yellow fever is common in rural areas of sub-Saharan Africa and tropical regions of South America and vaccination is usually recommended for travellers to these regions.

Is it safe to be vaccinated against yellow fever in pregnancy?

There is no yes or no answer to this question. The yellow fever vaccine is a live vaccine, which means that it contains live but inactivated yellow fever virus. Live vaccines are not usually recommended in pregnancy because there is a theoretical worry that an inactivated virus could reactivate in the body and be passed to the baby. However, yellow fever can be a life-threatening illness. When deciding whether to have the yellow fever vaccine during pregnancy it is important to weigh up the known risks of yellow fever against the possible but unconfirmed risks to you or your baby of being vaccinated in pregnancy, some of which might depend on how many weeks pregnant you are.

Having the yellow fever vaccine might be considered necessary if travel to an area where yellow fever is common cannot be avoided during pregnancy. Your doctor is the best person to help you decide what is right for you and your baby.

This leaflet summarises the scientific studies relating to the effects of yellow fever vaccine on a baby in the womb so that you can make an informed decision. 

What if I have been vaccinated against yellow fever during pregnancy?

If you have been vaccinated or are taking any medicines it is always a good idea to let your doctor know that you are pregnant. You can then decide together whether you still need the medicines that you are on and to make sure that you are taking the lowest dose that works.

Can being vaccinated against yellow fever in pregnancy cause my baby to be born with birth defects?

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.

Around 500 babies whose mothers used yellow fever vaccines in early pregnancy have been studied. Although there is no evidence that exposure in the womb to yellow fever vaccine increases the chance of birth defects in the baby, these studies cannot completely rule out the possibility of a link. More large, well-controlled scientific studies into the possible effects of exposure in the womb to yellow fever vaccines are therefore required.

Can being vaccinated against yellow fever in pregnancy cause miscarriage?

It is currently unclear whether miscarriage is more likely after yellow fever vaccination in pregnancy as there is not enough reliable scientific information on this subject. More research is therefore required.

Can being vaccinated against yellow fever in pregnancy cause stillbirth, preterm birth, or my baby to be small at birth (low birth weight)?

A single small study found that the likelihood of stillbirth, preterm birth and low birth weight in the baby was similar for women who had been vaccinated against yellow fever in pregnancy and women in the general population. However, because no large, high quality scientific studies have investigated whether use of yellow fever vaccines in pregnancy increases the risk of stillbirth, preterm birth, or low birth weight in the baby, further research into these pregnancy outcomes is therefore required.

Can being vaccinated against yellow fever in pregnancy cause learning and 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 single study of around 100 children exposed in the womb to yellow fever vaccine did not show any link with learning or behavioural problems by the age of 4 years. No further studies have investigated these outcomes and more research into this subject is therefore required.

Will my baby need extra monitoring during pregnancy?

As part of their routine antenatal care most women will be offered scan and blood tests from around 11 weeks of pregnancy and a further scan at around 20 weeks to look for birth defects in the baby. Being vaccinated against yellow fever in pregnancy is not expected to cause problems that would require extra monitoring of your baby.

Are there any risks to my baby if the father has been vaccinated against yellow fever?

No studies have specifically investigated whether yellow fever vaccine used by the father can harm the baby through effects on the sperm, however most experts agree that this is very unlikely. More research on the effects of medicine use in men around the time of conception is needed.

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 www.uktis.org.

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.

   

www.medicinesinpregnancy.org

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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