Pregnant women are considered to be at increased risk of complications from the influenza virus and influenza-associated death. The Department of Health and Health Protection Agency recommend vaccination against influenza in this group; at any stage of pregnancy
The vulnerability of pregnant women to the effects of influenza infection was made clear during the recent H1N1 ‘swine flu’ pandemic in 2009, caused by the influenza A(H1N1)pdm09 virus.
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 the A(H1N1)pdm09 virus than the general population. The risk increases in the third trimester of pregnancy; the last six months.
The World Health Organization (WHO) has reported that 7-10% of all hospitalised patients with the A(H1N1)pdm09 virus were pregnant women and they were more likely to need intensive care when compared with the general population.
In light of the evidence from the 2009 pandemic, pregnant women were added to the ‘at risk’ group for who the seasonal influenza vaccine is recommended.
Although the pandemic is over, the influenza A(H1N1)pdm09 virus is likely to be one of the main influenza strains circulating in the 2012/13 winter season and is likely to circulate globally in years to come.
The seasonal influenza vaccine for 2012/13 contains three flu strains one of which is the A(H1N1)pdm09 virus and this is the recommended vaccine for pregnant women.
The flu virus is constantly changing and each year the World Health Organisation makes recommendations about the strains to be included in influenza vaccines for the forthcoming winter. The seasonal flu vaccine for 2012/13 contains parts of A(H1N1)pdm09 virus and two other flu viruses that are predicted to be circulating.
The seasonal influenza vaccine for 2012/13 is licensed for use in pregnancy. It contains vaccine against three flu strains an influenza A/H3N2, A/H1N1 and an influenza B virus. The vaccine is grown in eggs, and contains inactivated virus. It does not contain live virus and cannot cause flu. It does not contain an adjuvant – a chemical designed to produce a greater immune response.
The seasonal flu vaccine generates a protective antibody response in your body to the three influenza viruses that are likely to be circulating this winter. The protection conferred by the vaccine is not 100% so there is still a small risk of catching flu and you should not ignore the signs and symptoms of influenza even if you have been vaccinated. If you do become infected with influenza the vaccine will protect you from the more severe forms of illness and death.
Influenza vaccination during pregnancy also provides passive immunity against influenza, through the transfer of maternal antibodies across the placenta, to infants in the first few months of life following birth (Benowitz et al, 2010; Eick et al, 2010).
No, the vaccine is safe, however, influenza infection can increase the risk of premature birth, which is why the Department of Health recommends all pregnant women should get vaccinated. One recently published study has shown that that influenza vaccination reduced the likelihood of prematurity and smaller infant size at birth associated with influenza infection (Omer et al, 2011).
The seasonal flu vaccination has been recommended in pregnancy for several years in many countries and has been shown to be safe in all stages of pregnancy (Tamma et al, 2009), including the first trimester (Sheffield et al, 2012).
Studies, and experience from other types of vaccines - both with and without adjuvants - have not raised concerns with the use of these vaccines during pregnancy.
Thiomersal has been used in vaccines as a preservative to reduce bacterial contamination. In 2004, EMEA concluded that the studies showed no association between vaccination with thiomersal containing vaccines and specific neuro-developmental 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 (Thomson et al, 2007).
While expert scientific advice is clear that thiomersal-containing vaccines do not present a risk to pregnant women or their babies, the only flu vaccine that contains any thiomersal is Fluvirin; even then it only contains traces of thiomersal that are left over from the manufacturing process.
The seasonal flu vaccine is freely available to all pregnant women and should be routinely offered by GPs to any pregnant women unless they have already recently received the seasonal vaccine.
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.
Omer SB, Goodman, D, Steinhoff, MC et al. Maternal influenza immunization and reduced likelihood of prematurity and small for gestational age births: a retrospective cohort study. PLoS Med. 8: [5.] e1000441 Epub 2011 May 31. 2011 May.
Sheffield JS et al. Effect of influenza vaccination in the first trimester of pregnancy. Obstet Gynecol 2012 Sep; 120:532.
Tamma PD, Ault KA, del Rio C, Steinhoff MC et al. (2009) Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol 201(6): 547-52.
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: 23 October 2012