Swine flu vaccination for pregnant women: frequently asked questions

As pregnant women are at increased risk of complications from swine flu, the Department of Health and the Health Protection Agency recommend vaccination for swine flu for pregnant women, at any stage of pregnancy.

Why should I have this vaccine when I am pregnant?
What swine flu vaccines have been licensed for use in pregnancy?
Which vaccine is recommended in pregnancy in the UK?
What do we know about the safety of swine flu vaccine in pregnancy?
Is the preservative used in the vaccine safe in pregnancy?
Bibliography

For further information, see the swine flu and pregnancy FAQ.

Why should I have this vaccine when I am pregnant?

Evidence from North America, Australia and Europe shows that pregnant women are at an increased risk of severe disease and admission to hospital with swine flu.

Studies from the US have shown that pregnant women are four times as likely to develop serious illness and they are four to five times more likely to be admitted to hospital with swine flu than the general population.

The World Health Organization (WHO) has reported that 7-10% of all hospitalised patients with swine flu are pregnant women and they are more likely to need intensive care when compared with the general population.

The risk increases in the third trimester of pregnancy (6-9 months).

What swine flu vaccines have been licensed for use in pregnancy?

The UK is using two different types of vaccine - Pandemrix® and Celvapan®.

• Pandemrix® is grown in eggs, and contains inactivated virus components. It contains an adjuvant, which boosts the immune response and reduces the dose of virus required, and a preservative (thiomersal). One dose is normally required for protection.
• Celvapan®, is grown on cultured cells (not eggs) and is a whole virus vaccine (it contains all the virus components). It does not contain an adjuvant. Two doses are required for protection.

Both vaccines are made from inactivated virus - they do not contain live virus and cannot cause flu.

The European Medicines Agency (EMEA) has licensed both vaccines for use in pregnant women. In licensing the vaccine, the European regulators gave careful consideration to the increased risk of complications caused by swine flu in pregnant women, the safety record of seasonal flu vaccines and the adjuvants that were used in the pandemic vaccines.

Both vaccines are being used for pregnant women in a number of countries worldwide.

Which vaccine is recommended in pregnancy in the UK?

Independent experts on the Joint Committee on Vaccination and Immunisation (JCVI) have recommended that pregnant women should be offered swine flu vaccine. Pandemrix is advised as it only requires one dose, so it gives more rapid protection than the two-dose vaccine.

What do we know about the safety of swine flu vaccine in pregnancy?

There is no evidence of risk from vaccinating pregnant women with inactivated virus vaccines.

The seasonal flu vaccination has been recommended for several years in many countries and has been shown to be safe in all stages of pregnancy. 

Reproductive toxicity studies, and experience from other types of vaccines - both with and without adjuvants - do not raise concerns with use during pregnancy.

Recent trials of both the swine flu vaccines which are licensed for use in the UK have shown that they produce the required immune response we expect to work against the virus.  This is expected to be similar to seasonal flu vaccines at around 70-80%.

Similar flu vaccines containing a different strain of flu virus (H5N1) have undergone clinical testing and trials show they are safe. Experience with seasonal flu vaccines have shown that changing the virus strain in a vaccine does not substantially affect the safety of the vaccine.

Of the women who became pregnant during the clinical trials with H5N1 vaccine using the same adjuvant, there is no evidence of any specific risks to the mother or fetus due to the vaccine.

Is the preservative used in the vaccine safe in pregnancy?

Thiomersal is used as a preservative in the Pandemrix vaccine to reduce bacterial contamination.
Expert scientific advice is clear that thiomersal-containing vaccines, such as Pandemrix, do not present a risk to pregnant women or their babies.

In 2004, EMEA concluded that the studies showed no association between vaccination with thiomersal containing vaccines and specific neurodevelopmental disorders.

Another more recent study has shown no association between neuropsychological functioning at age 7-10 years and exposure to thiomersal during the antenatal and neonatal periods, and the first seven months of life.

Bibliography

Jamieson D et al (2009) H1N1 2009 Influenza virus infection during pregnancy in the USA. Lancet 2009; 374: 451-458.

Pandemic (H1N1) 2009: Current pandemic risk assessment. European Centre for Disease Control (ECDC)website.

Plotkin SA Orenstein WA and Offutt PA (eds) (2008) Vaccines 5th Edition. Philadelphia WB Saunders Company.

EMEA/COMP/VEG/1194 (2004) EMEA public statement on thiomersal in vaccines  for human use - recent evidence supports safety of thiomersal-containing vaccines.

Thompson WW Price C Goodson B et al (2007) Early thiomersal exposure and neuropsychological outcomes at 7 to 10 years. N Eng J Med 2007; 357:1281-1292.

Last reviewed: 4 December 2009