The following news story appeared in Essentially MIDIRS, vol 5, no 10, November 2014, p13.
It is generally accepted that ‘pregnant women are at increased risk of getting serious complications from flu, compared with other healthy adults’ (Public Health England 2014:3). This is usually attributed to the fact that the immune system is weakened during pregnancy ‘to ensure that the pregnancy is successful’ (Public Health England 2014:3) — that is, to prevent the body from rejecting the growing fetus. Just as influenza season hits again however, fascinating new research (Kay et al 2014) has emerged which suggests that this might not be the case.
The researchers analysed immune cells taken from blood samples from 21 pregnant and 29 non-pregnant women which had been exposed to different flu viruses in the laboratory. The results suggest that an increase in serious complications of influenza in pregnancy may be related to an enhanced inflammatory response, rather than a suppressed immune system. Two types of white blood cells, natural killer-cells and T-cells, from the pregnant women exposed to the virus, were found to produce particularly high levels of cytokines and chemokines compared with the white blood cells in the non-pregnant women. The function of such cells is to attract immune cells to the site of the infection, and where an excess of white blood cells is produced an excess of immune cells occurs, so reducing the space for air in the lungs and increasing the risk of pneumonia and other complications.
If these initial findings are borne out by further studies, it will have obvious repercussions for the treatment of flu in pregnancy. Although it would still be useful to use treatments that slow viral replication, new immune-modulating approaches would also need to be developed. Catherine Blish, the study’s senior author, also speculated whether the inflammatory response could explain why contracting influenza in pregnancy increases the risk of preterm birth: “I wonder if this is an inflammatory pathway that is normally activated later in pregnancy to prepare the body for birth, but that flu happens to overlap with the pathway and aberrantly activates it too early”. The authors of this study called for more pregnant women to be vaccinated against influenza, stating that “Flu vaccination is very important to avoid this inflammatory response we’re seeing”. Encouraging greater levels of vaccination also highlights the need for increased transparency from pharmaceutical companies in matters of trial data for new drugs, following criticism of Roche for its handling of data for Tamiflu, after the Cochrane Collaboration spent four and a half years trying to obtain complete trial data in order to assess the effectiveness of the drug in the prevention and treatment of influenza. The systematic review (Jefferson et al 2014), published in April of this year suggested that once all the data were taken into account, Tamiflu and Relenza — a similar drug marketed by GlaxoSmithKline — were less effective than had been previously thought.
As a result of these revelations NICE recently announced that it has strengthened its process guide so that medical directors must sign a declaration stating they have identified all clinical trial data when making submissions to the organisation. This should help to ensure that NICE has the complete picture required to develop evidence-based recommendations. It is essential that recommendations are built on trustworthy data, not just from a health perspective, but also from a financial point of view — it has been estimated that the UK government spent £473 million on Tamiflu and £136 million on Relenza, based on an assessment made on partial data (AllTrials 2014).
AllTrials (2014). We need results from all clinical trials to make decisions about medicines, Tamiflu Relenza study shows. [Accessed 1 October 2014].
Jefferson T, Jones MA, Doshi P et al (2014). Neuraminidase inhibitors for preventing and treating influenza in healthy adults and children. Cochrane Database of Systematic Reviews, Issue 7. [Accessed 30 September 2014].
Kay AW, Fukuyama J, Aziz N et al (2014). Enhanced natural killer-cell and T-cell responses to influenza A virus during pregnancy. PNAS (Proceedings of the National Academy of Sciences of the United States of America), 22 September [Online ahead of print].
Public Health England (2014). Flu, your pregnancy and you. London: TSO. [Accessed 29 September 2014].
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