Background information on the safety of rubella-containing vaccines given in pregnancy

1. What is the risk if you have MMR (measles, mumps, rubella) vaccine whilst you are pregnant or shortly before falling pregnant?

There is no known risk if you are immunised with rubella, measles-rubella (MR) or MMR vaccine whilst pregnant or shortly before becoming pregnant. MMR vaccine is not recommended in pregnancy as matter of caution, and it is for the same reason that we wish to follow all women who are given the vaccine by accident whilst pregnant.

2. What is the evidence that MMR (measles, mumps, rubella) vaccine is safe in pregnancy?

In the USA, UK and Germany, hundreds of women have been followed through active surveillance since the 1970s. This includes 293 who were vaccinated with rubella-containing vaccine within six weeks of their last menstrual period. None of the babies had permanent abnormalities compatible with congenital rubella syndrome (CRS) (See section 3)¹. A small number of babies (around 16) had evidence that they had been exposed to the weakened vaccine virus (from blood tests) but there was no sign that the vaccine had affected the development of the infant.

Recent very large measles-rubella vaccination campaigns (run between 2001 and 2008) have targeted women of child-bearing age in South America and Iran^2,3,4,5,6. Comprehensive, prospective surveillance of pregnant women during these campaigns has provided further substantial evidence of the safety of measles and rubella containing vaccines in pregnancy. During these campaigns over 30,000 pregnant women inadvertently received MR vaccine. The vaccine had been given either during pregnancy (the majority were less than 12 weeks pregnant) or up to 30 days before they had conceived.

In the above studies about 3000 women were susceptible to rubella - meaning they were not already immune and so at potential risk of the virus passing to the baby. Extensive follow-up of the outcome of these pregnancies was very reassuring. Whilst a very small number of babies were shown to have been exposed to the weakened vaccine virus in the womb, no babies developed CRS. There was also no increase in the risk of miscarriage or stillbirth in pregnant women who were susceptible (non-immune) when they were vaccinated when compared to those protected by prior immunity⁷. 
 

In contrast, when a woman has natural rubella infection (german measles) in the first 20 weeks of her pregnancy her baby may be affected. This can lead to the baby being born with developmental abnormalities – this is called congenital rubella syndrome (See section 4). These large-scale vaccination programmes were carried out at a time when natural rubella infection was high in those countries and so it is very unlikely that an infant with the clinical features of CRS would be missed ². During 2001-2002, 56 infants with CRS were reported to the San Paulo State Health Department. None of these were born to mothers vaccinated in pregnancy and so it was concluded that all were due to natural infection.⁷

Therefore, there are no safety concerns, either for the mother or the baby, when rubella-containing vaccine is given in pregnancy or shortly prior to pregnancy. Women who have been immunised with MMR or single rubella vaccine in pregnancy can therefore be immediately reassured. Such an incident would not be a reason to recommend termination of pregnancy⁸.
 

3. Why are you following up women who are given MMR vaccine whilst pregnant or shortly before becoming pregnant?

A registry was established in 1981 specifically for rubella vaccine, originally under the National Congenital Rubella Surveillance Programme. Rubella vaccine has since been replaced with combined MMR vaccine. The surveillance programme was set up to address theoretical concerns from vaccinating pregnant women with live rubella vaccine virus. This was because of the known risk of congenital rubella syndrome after natural rubella infection (german measles) in early pregnancy. Information from surveillance of these cases in the UK has been included in the figures in section 5 and has helped provide additional assurance of the lack of risk from the rubella vaccine virus in pregnancy.

The UK Vaccine in Pregnancy surveillance programme is run by the Immunisation Department of the Health Protection Agency Centre for Infections http://www.hpa.org.uk/. The objectives of the UK Vaccine in Pregnancy surveillance are to compile additional information on women who are immunised with specified vaccines whilst pregnant. These data will be used to help better inform pregnant women who are inadvertently immunised, their families and health professionals who are responsible for their care.
 

4. What is the risk from natural rubella infection?

When a woman has natural rubella infection in the first 20 weeks of her pregnancy the baby is also at risk from the infection. The risk to the baby from rubella infection during the first 16 weeks of pregnancy is substantial, with major and varied congenital abnormalities being associated with infection at this time; commonly known as congenital rubella syndrome (CRS). If rubella infection occurs between 16 and 20 weeks of pregnancy, there is a risk that the child will be deaf. In contrast, rubella-containing vaccine contains a weakened strain of the rubella virus and there is no known risk associated with giving rubella or MMR vaccine whilst pregnant or shortly before becoming pregnant. Rubella infection prior to the date of conception, or after 20 weeks of pregnancy, carries no documented risk.
 

5. What difference has rubella-containing vaccine made to Congenital Rubella Syndrome (CRS) in the UK?

In 1970 a schoolgirl rubella immunisation programme was introduced in the UK. This selective policy was effective in reducing the number of children born with CRS (see graph) but rubella continued to circulate and any remaining non-immune women were often exposed via their own or other young children. Measles, mumps and rubella (MMR) vaccine was introduced in 1988 for all children in the second year of life, with the aim of interrupting circulating rubella.

In 1994, a national measles/rubella vaccine campaign targeted all school aged children (5 to 16 years) in 1994 and the schoolgirl vaccination programme was discontinued. A routine second MMR immunisation at 4 years of age was subsequently introduced in 1996,

Before rubella vaccine became available, an estimated 200-300 babies were born each year with CRS in the UK. In the ten years between 2002 and 2011 there have been 8 cases of CRS born in England and Wales, of whom 4 were infected abroad.
 

Graph: Babies born with Congenital Rubella Syndrome between 1970 and 2007 in England and Wales.

Source: National Congenital Rubella Surveillance Programme and Health Protection Agency Centre for Infections

6. Who are you following up?

We are following up women who have received MMR vaccine from 30 days prior to their last menstrual period or at any time in pregnancy.
 

¹Best JM, Cooray S, Banatvala JE. Rubella. In: Mahy BMJ and ter Meulen V (eds) Topley and Wilson’s Virology, 10th edition. London (2004): Hodder Arnold.
²Castillo-Solorzano C, Reef SE, Morice A et al. Rubella Vaccination of Unknowingly Pregnant Women During Mass Campaigns for Rubella and Congenital Rubella Syndrome Elimination, The Americas 2001-2008. J Inf Dis 2011;204:S713-717.
³Da Silva e Sa GR, Camacho LAB, Stavola MS et al. Pregnancy Outcomes Following Rubella Vaccination: A Prospective Study in the State of Rio de Janeiro, Brazil, 2001-2002. J Inf Dis 2011;204:S722-728.
⁴Soares RC, Siqueria MM, Toscano CM et al. Follow-up Study of Unknowingly Pregnant Women Vaccinated Against Rubella in Brazil, 2001-2002. J Inf Dis 2011;204:S729-736.
⁵Hamkar R, Jalilvand S, Abdolbaghi MH et al. Inadvertent rubella vaccination of pregnant women: Evaluation of possible transplacental infection with rubella vaccine. Vaccine 2006;24:3558-3563.
⁶Namaei MH, Ziaee M & Naseh N. Congenital rubella syndrome in infants of women vaccinated during or just before pregnancy with measles-rubella vaccine. Indian J Med Res 2008;127:551-554.
⁷Sato HK, Sanajotta AT, Moraes JC et al. Rubella Vaccination of Unknowingly Pregnant Women: The Sao Paulo Experience, 2001. J Inf Dis 2011;204:S737-744.
 ⁸Tookey PA, Jones G, Miller BH, Peckham CS. Rubella vaccination in pregnancy. CDR London Engl Rev 1991; 1(8): R86-8.

Last reviewed: 18 May 2012