2009 A/H1N1 influenza vaccination in pregnancy: uptake and pregnancy outcomes – a historical cohort study

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Abstract

Objectives

To describe the uptake of 2009 A/H1N1 influenza vaccination among pregnant women and determine if vaccination was associated with adverse pregnancy outcomes.

Study Design

A historical cohort study was performed using booking, delivery suite and neonatal unit discharge records from the Coombe Women and Infants University Hospital, Dublin, Ireland. Singleton deliveries to women pregnant before (December 2008–September 2009) and during the pandemic (December 2009–September 2010) were included.

Information on vaccination status and type of vaccine was collected on admission to the delivery suite. Logistic regression analyses were used to determine maternal characteristics associated with vaccination. Pregnancy outcomes were compared for vaccinated and unvaccinated women, with adjustment for differing maternal characteristics. Outcomes included vaccination status, preterm birth, size for gestational age, neonatal intensive care admission, congenital anomalies and perinatal death.

Results

Of 6894 women pregnant during the pandemic, 2996 [43.5%] reported vaccination at delivery. In the early weeks of the vaccination programme rates of over 70% were achieved. Of those vaccinated, 246 [8.2%], 1709 [57.0%] and 1034 [34.5%] were vaccinated in the first, second and third trimesters respectively. Vaccination was less likely in younger age groups, those who were not in the professional/manager/employer socioeconomic group, women from Eastern Europe, Africa and Asia/Middle East, those who reported an unplanned pregnancy, women who booked late for antenatal care and recipients of publicly-funded obstetric care. Irish nationality was associated with reporting vaccination. There was no association between vaccination during pregnancy and adverse pregnancy outcomes. Women who were vaccinated were less likely to have a preterm delivery than unvaccinated women.

Conclusion

2009 A/H1N1 influenza vaccination uptake was influenced by maternal sociodemographic factors. High vaccination uptake can be achieved in a pandemic situation. Future public health campaigns should provide clear information on vaccination safety in pregnancy, ensure consistent vaccination recommendations from healthcare professionals and provide easy access to vaccination in order to optimise uptake rates in subgroups of the population who less likely to be vaccinated. There was no association between vaccination and adverse pregnancy outcomes.

Introduction

Pandemic 2009 A/H1N1 influenza infection appeared to increase the risk of severe maternal morbidity and mortality and was associated with adverse pregnancy outcomes [1], [2], [3], [4], including perinatal death [1]. Previous pandemics also demonstrated the risk of serious adverse maternal and fetal outcomes [5]. In order to reduce the risk of such adverse outcomes vaccinations against pandemic 2009 A/H1N1 influenza were licensed and recommended for use during pregnancy [6]. In Ireland two vaccines were commercially available and recommended for use in the national immunisation campaign: Pandemrix®, an egg-derived vaccine containing thiomersal and the AS03 adjuvant (dl-α-tocopherol, squalene and polysorbate); and Celvapan®, a cell-line-derived, thiomersal free, non-adjuvanted alternative.

Seasonal influenza vaccines have been administered to pregnant women since the late 1950s [7], and the US Advisory Committee on Immunization Practices (ACIP) has, since 2004, encouraged pregnant women to be vaccinated against seasonal influenza regardless of gestation [8]. Uptake rates of 2009 A/H1N1 influenza vaccine varied internationally during the pandemic with studies reporting rates in pregnant women from as low as 4.7% to as high as 85% [9], [10], [11]. Variations in international recommendations relating to the optimal timing of vaccination in pregnancy, the selection of non-adjuvanted vaccines for pregnant women and the need for seasonal influenza vaccination in pregnancy led to media commentaries, speculation on vaccine safety and public anxiety.

Available data support the use of the inactivated influenza vaccine during all stages of pregnancy, particularly for women with medical conditions that may increase the risk of complications. Reassuring pharmacoepidemiological studies have indicated that 2009 A/H1N1 influenza vaccination is not associated with adverse pregnancy outcomes including fetal death, preterm birth and congenital anomalies [12], [13], [14], [15], [16], [17]. Vaccination may have reduced the risk of influenza-related fetal death during the pandemic [12].

It is important to study the determinants of vaccination uptake in pregnant women in a variety of settings, given the regional variations that have been previously reported [18]. It is also essential that extensive data are available on pregnancy outcomes after gestational vaccine exposure in order to inform decisions on vaccination by pregnant women and health professionals, particularly during a pandemic situation. This study has two main objectives. The first objective is to describe the uptake and determinants of 2009 A/H1N1 influenza vaccination in pregnant women during the pandemic. The second objective is to determine if there is an association between vaccination and adverse pregnancy outcomes.

Section snippets

Materials and methods

The Irish pandemic flu vaccination programme began in early November 2009 and ended on the 31st of March 2010 [19]. In the initial phase high risk groups, including pregnant women, were offered prioritised access to the vaccine. Vaccination was offered in vaccination centres set up by the Health Service Executive, in vaccination clinics run by the maternity hospital to coincide with antenatal clinics and in primary care. Details of vaccination provider were not available for this study.

All

Vaccine uptake

Of 6894 women delivering between the beginning of December 2009 and the end of the following September, 2996 women [43.5%] reported vaccination at delivery. The temporal distribution of vaccination during pregnancy is represented in Fig. 1. Vaccination in the first, second and third trimesters was reported by 246 [8.2%], 1709 [57.0%] and 1034 [34.5%] vaccinated women, respectively. Celvapan® was received by 1692 [56.5%] women, with approximately half receiving a single dose and half receiving

Main findings

This study demonstrated that 43.5% of women delivering between December 2009 and September 2010 had received at least one dose of pandemic 2009 A/H1N1 influenza vaccine, with vaccination rates of over 70% in the weeks after the initiation of the vaccination programme. Of the women with known vaccine type, the majority [70.7%] received the cell-line-derived, thiomersal free, non-adjuvanted product Celvapan®. Women who were less likely to be vaccinated included those in younger age groups, those

Strengths and limitations

This study was conducted in a large tertiary referral maternity hospital that delivers approximately 9000 babies annually. Data on maternal characteristics, medical history, vaccination status and pregnancy outcomes were routinely collected by midwives using structured computer-guided and paper questionnaires. Data were available on a diverse group of women from a broad range of socio-economic groupings. Virtually all deliveries during the study period were included in the analysis, reducing

Interpretation

There are a number of factors that may have an impact on vaccination uptake rates in the pregnant population. Maternal characteristics associated with vaccination include working outside the home, being multiparous and having a higher level of education [21]. Other factors include the safety concerns of both patients and healthcare workers and also a lack of recommendation of vaccination by medical professionals [22]. A US survey of postpartum women, which reported a vaccination rate of 34%,

Conclusion

This study demonstrates that high influenza vaccine uptake rates can be achieved for pregnant women in a pandemic situation. Future public health campaigns should provide clear information on vaccination safety in pregnancy, ensure consistent advice and vaccination recommendations from healthcare professionals and provide easy access to vaccination e.g. through integration with antenatal care to optimise uptake rates in subgroups of the population who are less likely to be vaccinated.

Reassuring

Disclosure of interests

None of the researchers have any conflict of interest to declare. No contractual constraints on publishing were imposed by the funding bodies.

Contribution to authorship

BC proposed the study initially and was responsible for study design along with UR, ME and FM; BC, UR and NM were responsible for acquisition and analysis of data; all authors were involved in drafting the article, revising it and final approval for publication.

Details of ethics approval

The study was approved by the Hospital’s Research Ethics Committee on 16th May 2012 (Study No. 3–2012).

Funding

BC was funded by the charity Friends of the Coombe and the School of Pharmacy, Royal College of Surgeons in Ireland.

Acknowledgements

We would like to gratefully acknowledge the funders: the Friends of the Coombe and the School of Pharmacy, Royal College of Surgeons in Ireland; Dr. Chris Fitzpatrick and Ann Fergus for facilitating data collection; the Midwives and other staff who collected the data and Emma McNamee from the IT Department for extracting the data.

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