Volume 198 - Issue 7
Evidence-based policies for the control of influenza
Authors: Heath A Kelly and Nicholas Kelley
Med J Aust 2013; 198 (7): 349-350. || doi: 10.5694/mja13.10294
Published online: 15 April 2013
Published online: 15 April 2013
Vaccination remains the single best option for controlling influenza, but it is important not to overstate the effectiveness of current inactivated vaccines.
Influenza vaccines can prevent serious outcomes of infection, but vaccine policies should be based on the best contemporary evidence
In this issue of the Journal, two studies draw attention to potential difficulties in protecting vulnerable people from influenza infection. In the first study, Wiley and colleagues report a 27% uptake of influenza vaccine by pregnant women in three hospitals in New South Wales in 2011, with differences in uptake attributable to how the vaccine was promoted and the ease of accessing it.1 Influenza vaccination of pregnant women is an important issue that was highlighted during the 2009 pandemic. In Australia, the risk of hospitalisation with pandemic (H1N1) 2009 influenza for pregnant women compared with non-pregnant women aged 15–44 years was increased by about fivefold2 and the risk of admission to intensive care, by about sevenfold.3 The World Health Organization recently recommended influenza vaccination for pregnant women as the highest priority for countries considering initiation or expansion of programs for seasonal influenza vaccines.4
In the second study, Macesic and colleagues estimated that 4% of almost 600 cases of laboratory-proven influenza in sentinel Australian hospitals in 2010 and 2011 were acquired in hospital.5 Although the estimated risk was low, the outcome could be severe. One patient with end-stage respiratory disease died, and 23% of patients required intensive care. Hospitals should be safe places, and acquiring influenza as an inpatient is potentially preventable. Prevention involves five arms: cohorting or isolation of patients with suspected infection; studious attention to respiratory precautions and hand hygiene; preventing staff and visitors with respiratory symptoms from entering the facility; vaccination of everyone with patient contact, including health care workers, visitors and family members; and vaccination of patients.
Influenza vaccination is recommended in the Australian immunisation handbook for patients at increased risk of an adverse outcome from influenza infection, and is funded for these patients.6 All the patients with hospital-acquired influenza in Macesic et al’s study had comorbidities that rendered them eligible for free influenza vaccine, but only 36% had been vaccinated.5 To protect themselves and their patients, the Australian immunisation handbook also recommends that health care workers be vaccinated.6
Vaccination can help prevent influenza infection in pregnant women and hospital inpatients, but it is not a perfect intervention. For many years it has been suggested that trivalent inactivated influenza vaccine provided protection to 70%–90% of participants in randomised controlled trials (RCTs).4,6 However, a more recent estimate from a meta-analysis of vaccines licensed in the United States suggested that protection for adults under the age of 65 years, even in the controlled environment of the RCT, was around 59%.7 A large RCT conducted in Australia and New Zealand during the 2008 and 2009 influenza seasons estimated efficacy as 42% (95% CI, 30%–52%) against all strains of influenza, including the pandemic (H1N1) 2009 influenza virus, while the point estimate for matched strains was 60%. The higher efficacy against vaccine strains matched to circulating strains is expected.8 Participants in RCTs are generally young and healthy, whereas influenza vaccines are funded in Australia for people who are older or have underlying medical conditions, for whom the vaccine may be less effective.
How then do trial results compare with estimates from the field? Recent observational studies from Australia of influenza vaccine effectiveness in routine practice are broadly supportive of estimates from the trials.7,8 Over the period from 2007 to 2011, but excluding the pandemic year of 2009, influenza vaccine effectiveness among adults aged 20–64 years presenting to sentinel general practices in Victoria was estimated as 62% (95% CI, 43%–75%).9 In a study of sentinel Australian hospitals in 2010, vaccine effectiveness against hospitalisation with confirmed pandemic (H1N1) 2009 influenza, the dominant circulating virus that year, was estimated as 49% (95% CI, 13%–70%).10
Trial results can legitimately be compared with Australian observational studies because most of the vaccines used in the trials were trivalent inactivated vaccines, the only type of vaccine currently licensed in Australia, and the end points in all studies were laboratory-confirmed, medically attended influenza. There are no specific vaccine effectiveness estimates for pregnant women or health care workers in Australia, but it is not unreasonable to expect effectiveness for these two groups to be in the range for other adults.
It is important to continue to promote influenza vaccination as a cornerstone of protection against infection and adverse outcomes, but it is also important not to overstate the effectiveness of current inactivated vaccines. Estimates that are not based on contemporary evidence have the potential to undermine confidence in the vaccine. Although not ideal, a vaccine that may protect around half of all recipients from an infection requiring medical attention (a general practitioner visit or hospital admission) can definitely be recommended. Vaccination remains the single best option for controlling influenza, but improved vaccines will make policy setting and promotion of vaccination much easier.11,12
Competing interests
No relevant disclosures.
References
- Wiley KE, Massey PD, Cooper SC, et al. Uptake of influenza vaccine by pregnant women: a cross-sectional survey. Med J Aust 2013; 198: 373-375.
- Kelly H, Mercer G, Cheng A. Quantifying the risk of pandemic influenza in pregnancy and Indigenous people in Australia in 2009. Euro Surveill 2009; 14: pii 19441. 0_i1139908
- ANZIC Influenza Investigators and Australasian Maternity Outcomes Surveillance System. Critical illness due to 2009 A/H1N1 influenza in pregnant and postpartum women: population based cohort study. BMJ 2010; 340: c1279. doi: 10.1136/bmj.c1279. 0_i1139910
- World Health Organization. Vaccines against influenza: WHO position paper – November 2012. Wkly Epidemiol Rec 2012; 87: 461-476. 0_i1139912
- Macesic N, Kotsimbos TC, Kelly P, Cheng AC; FluCAN investigators. Hospital-acquired influenza in an Australian sentinel surveillance system. Med J Aust 2013; 198: 370-372. 0_i1139914
- National Health and Medical Research Council. Influenza. In: Australian immunisation handbook. 9th ed. Canberra: NHMRC, 2008. http://immunise.health.gov.au/internet/immunise/publishing.nsf/Content/Handbook-influenza (accessed Nov 2012).
- Osterholm MT, Kelley NS, Sommer A, Belongia EA. Efficacy and effectiveness of influenza vaccines: a systematic review and meta-analysis. Lancet Infect Dis 2012; 12: 36-44. 0_i1139918
- CSL Limited. A study of the efficacy, safety and tolerability profile of CSL Limited’s influenza virus vaccine (CSL’s IVV) administered intramuscularly in healthy adults. http://clinicaltrials.gov/ct2/show/NCT00562484 (accessed Mar 2013).
- Kelly HA, Sullivan SG, Grant KA, Fielding JE. Moderate influenza vaccine effectiveness with variable effectiveness by match between circulating and vaccine strains in Australian adults aged 20-64 years, 2007-2011. Influenza Other Respir Viruses 2012; 19 Oct. doi: 10.1111/irv.12018. 0_i1139922
- Cheng AC, Kotsimbos T, Kelly HA, et al. Effectiveness of H1N1/09 monovalent and trivalent influenza vaccines against hospitalization with laboratory-confirmed H1N1/09 influenza in Australia: a test-negative case control study. Vaccine 2011; 29: 7320-7325. 0_i1139924
- Nicoll A, Sprenger M. Low effectiveness undermines promotion of seasonal influenza vaccine. Lancet Infect Dis 2013; 13: 7-9. 0_i1139927
- Osterholm MT, Kelley NS, Manske JM, et al. The compelling need for game-changing influenza vaccines: an analysis of the influenza vaccine enterprise and recommendations for the future. Minneapolis: University of Minnesota Center for Infectious Disease Research and Policy, 2012. http://www.cidrap. umn.edu/cidrap/center/mission/articles/ccivi-landing.html (accessed Mar 2013).
Provenance: Commissioned; externally peer reviewed.