Flu vaccine in pregnancy

Key vaccine facts

Catching flu in pregnancy can lead to increased risks for both pregnant woman and their babies. Vaccination against flu reduces these risks. Serious complications of flu include pneumonia, septic shock (a severe and life-threatening infection of the whole body), meningitis and encephalitis (inflammation of the brain). Around 600 people die from complications of flu every year in the UK.

There is strong evidence that pregnant women have a much higher risk of serious illness as a result of flu, compared with the general population. The risks are highest in the last three months of pregnancy. US studies of the H1N1 (‘Swine Flu’) pandemic in 2009 found that pregnant women were four times as likely to develop serious illness and up to five times as likely to be admitted to hospital, compared with the general population. As a result of the evidence from this pandemic, pregnant women were added to the list of groups considered to be at higher risk from seasonal flu.

In the UK between 2009 and 2012, flu was the cause of death for 36 women who died during pregnancy or shortly afterwards. It is estimated that half of these deaths could have been prevented by flu vaccination. See the summary report from MBRRACE-UK (Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the UK).

There is also strong evidence that catching flu in pregnancy has an effect on the unborn baby. Babies born to women who have had flu are up to four times more likely to be born prematurely and to have a low birth weight. This may be because flu infection produces an inflammatory response in the body which can trigger premature labour. Flu in pregnancy can even lead to stillbirth or death in the first week of life.

Studies have shown that women who have been vaccinated against flu are less likely to give birth prematurely, and less likely to have a low-birthweight baby (see the results of a Canadian study ). Other studies have shown that women who have the flu vaccine while pregnant are less likely to experience stillbirth (see the results of an Australian study ).

Flu vaccination in pregnancy also means that flu antibodies are transferred through the placenta to the baby, who thus has protection against flu for the first few months of life.

Flu vaccination is offered to all pregnant women in the UK, as well as to other groups at high risk of flu. The vaccine can be given at any stage of pregnancy. The flu vaccine can safely be given to pregnant women at the same time as the pertussis vaccine. In the 2015-16 flu season, 42% of pregnant women in England (over 305,000 women) received the flu vaccine.

The vaccine is inactivated, and cannot cause flu itself.

See pages on Influenza (Flu) and the Flu vaccine for more general information.


Most inactivated flu vaccines contain very small amounts of egg proteins (ovalbumin), as the virus is often grown on hens’ eggs. People who are allergic to eggs should ask their doctor if there is an egg-free flu vaccine available. With specialist medical advice, they may also be able to receive a vaccine with a very low ovalbumin content. See more information on egg proteins in vaccines and an information sheet from Public Health England showing the ovalbumin content of flu vaccines in the 2016/17 season .

None of the adult flu vaccines to be used in the UK in the 2015-2016 season contain the preservative thiomersal (mercury).

There are several different makes of flu vaccine available each year. For full information on ingredients, ask for the Patient Information Leaflet for the vaccine you are offered. Inactivated flu vaccines used in the UK may contain very small amounts of the following ingredients:

  • Sodium and potassium salts, used as acidity regulators
  • A trace of antibiotic (gentamicin, neomycin or polymyxin)
  • A trace of formaldehyde, an organic compound used in the manufacturing process
  • Polysorbate, used as an emulsifier (to hold other ingredients together)

Side effects

The most commonly reported side effects of flu vaccines are: pain, swelling or redness at the injection site, slightly high temperature, headache, feeling a bit unwell, shivering, or tiredness.

As with any vaccine, medicine or food, there is a very small chance of a severe allergic reaction (anaphylaxis). Anaphylaxis is different from less severe allergic reactions because it causes life-threatening breathing and/or circulation problems. It is always serious but can be treated with adrenaline. In the UK between 1997 and 2003 there were a total of 130 reports of anaphylaxis following ALL immunisations, but all of these people survived. Around 117 million doses of vaccines were given in the UK during this period, making the overall rate around 1 in 900,000. Depending on the cause of the reaction, and following expert guidance, the person may be able to have vaccinations in the future.

There are several different makes of flu vaccine available each year. For more information on side effects, ask for the Patient Information Leaflet for the vaccine you are offered. Reactions listed under ‘possible side effects’ or ‘adverse events’ on vaccine product information sheets may not all be directly linked to the vaccine. See Vaccine side effects and adverse reactions for more information on why this is the case.

See more information on the monitoring of vaccine safety.

Does the vaccine work?

A study in England during the 2013/14 flu season showed that flu vaccination in pregnancy was effective in preventing flu in infants, and also effective in preventing hospitalisation of infants with flu.

A 2014 Canadian study of over 12,000 pregnant women showed that women who have been vaccinated against flu are less likely to give birth prematurely, and less likely to have a low-birthweight baby.

A 2016 Australian study of 58,000 births found that women who had the flu vaccine while pregnant were 51% less likely to experience stillbirth than those who were not vaccinated.

A 2016 US study of over 245,000 pregnant women found that babies aged 6 months and younger were much less likely to catch flu if their mothers had been vaccinated against flu when pregnant. Babies in this group showed a 70% reduction in laboratory-confirmed flu cases and an 80% reduction in flu-related hospitalisations, compared with babies whose mothers were not vaccinated. 97% of laboratory-confirmed flu cases occurred in babies whose mothers were not vaccinated against flu while pregnant.

Is the vaccine safe?

Seasonal flu vaccination has been recommended in pregnancy for several years in many countries. An increasing number of studies have shown it to be safe in all stages of pregnancy, including the first three months, and to have an important reduction in serious complications for the mother and baby. Read the abstracts of a US study from 2009 and a US study from 2012 .

Page last updated: 
Monday, October 24, 2016

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