Learning from the South: influenza immunization in pregnancy

Writing from Dhaka, Bangladesh, Jocalyn Clark celebrates the impact of a paper by Bangladeshi researchers on Western medical provision.

When two worlds collide in global health it can be a marvelous thing. Take for example the fact that although countries like the US and UK have recommended influenza immunization during pregnancy for many years, there was no evidence from a randomized controlled trial (RCT) to support the importance of that policy for birth outcomes until now. And the RCT to provide the needed evidence was not done in North America or Europe, but in Bangladesh by an international team, providing critical insights to help guide clinical practice, immunization policy, and women’s informed decision-making.

Image Credit: Steven Depolo, Flickr

Image Credit: Steven Depolo, Flickr

The Bangladesh evidence, drawn from secondary analyses of an RCT involving 340 pregnant women, shows that a flu shot given in the third trimester increased the mean birth weight of infants by 200 grams. These data are valuable for evidence-based health policy and care: women who get flu during pregnancy (especially late pregnancy) may risk complications for themselves or their babies, and yet there is low uptake of vaccination – in Canada, for example, less than one in five pregnant women has had a recent flu shot.

The low uptake may be because previous findings on influenza immunization in pregnancy and birth outcomes have been mixed: North American studies conducted during the 2009 pandemic suggested that vaccination reduced the risk of preterm birth, but most studies done during ordinary flu seasons have not found a link between vaccination and lower risk of prematurity.

The 2012 paper reporting the Bangladesh results has received renewed attention, being awarded last month the top paper in the CMAJ, Canada’s leading medical journal, for its originality, potential to impact practice, and methodological rigour. The award honours former editor Bruce Squires, who was a leader in evidence-based medicine and medical journalism, setting new standards for the ethics of research reporting. Dr Squires passed away in 2011 after a distinguished career in medicine and editing, having among other roles served as a founding member of both the World Association of Medical Editors and the Forum of African Medical Editors.

John Fletcher, CMAJ’s editor in chief emphasized the value of learning from the south when citing the award:  “this is a particularly good example of a trial that will make a difference to clinical practice. Although this paper is about women in Bangladesh, it speaks directly to Canadians’ healthcare and reassures Canadian women that the flu shot is good for them and their baby.”

The Bangladesh study was part of the Mother’s Gift project examining the safety and effectiveness of pneumococcal and influenza vaccines in pregnant women that previously reported in the New England Journal of Medicine a significant reduction in influenza infection and respiratory illness with maternal influenza immunization. The trial enrolled 340 healthy pregnant women in their third trimester; 170 participants were randomly assigned to receive influenza vaccine and the other 170 to receive pneumococcal vaccine as control.
In the new study, researchers compared the weight of babies born during a circulation of an influenza virus, and again when there was limited circulation of virus. When the virus was circulating, fewer babies were born who were small for gestational age in the influenza vaccine group (25.9%) than in the control group (44.8%), and the mean birth weight was 3,178 g in the influenza vaccine group, 7% higher than birth weight in control group (2,978 g). The rate of premature births was also lower in the influenza vaccine group. For both groups, the proportion of small-for-gestational-age births was similar when the virus was not circulating.

Several issues in the study bear acknowledging: Bangladesh has a high rate of low birth weight babies generally due to malnutrition (not influenza infection), and according to the authors no gold standard for size at gestational age exists there, so a North American standard was used. A pneumococcal vaccine was used as control, not placebo. Funding for the joint US-Bangladesh team study came from the Bill & Melinda Gates Foundation, USAID, Wyeth Pharmaceuticals Inc., Thrasher Research Fund, icddr,b, and the Bloomberg School of Public Health at Johns Hopkins University.

Subsequently, WHO recommendations, expert consultations, and additional studies have affirmed the benefits of influenza immunization in pregnancy.

Jocalyn Clark (@jocalynclark), a former Senior Editor at PLOS Medicine and former Assistant Editor at BMJ, is since November 2013 executive editor and scientific writing specialist at icddr,b in Dhaka, Bangladesh. She declares no competing interests.

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