12 May 2017

Studies urge greater flu vaccine uptake

"Be like me, be flu free" says the bandaid
of 2017 Day of Immunology vaccination café
participant Dr Dimitra Zotos
by Anne Crawford

As the flu season sets in, studies by Monash University researchers have reinforced the need for at-risk groups to have influenza vaccinations.

The two studies were led by Professor Allen Cheng, (Department of Epidemiology and Preventive Medicine), and Associate Professor Tom Kotsimbos (Department of Respiratory Medicine) in association with other researchers who are part of FluCAN (the Influenza Complications Alert Network), a sentinel surveillance program of 17 hospitals operating throughout Australia.


The first study, the annual assessment of the 2015 flu season (1 April to 30 October), found that 2,070 patients were admitted to the sentinel hospitals with confirmed influenza. Of these, 46% were elderly (65 years and over), 15% were children (less than 16 years), 5% were Indigenous Australians, 2.1% were pregnant and 75% had chronic co-morbidities.

While similar to that reported in 2014, the figure represented the largest number of admissions documented since hospital-based surveillance commenced in 2009. Extrapolated, this is likely to represent around 17,000 admissions nationally although this figure was probably an underestimate as influenza testing is not performed on all patients with acute respiratory presentations, the authors said.

The national immunisation program was estimated to have averted 46% of admissions with confirmed influenza, but more complete vaccination coverage in target groups could further reduce influenza admissions by as much as 14%, they said. Around half the influenza cases recorded were unvaccinated.

The Australian Government provides free vaccines for at-risk people: the elderly, pregnant women, Indigenous people and those with underlying medical conditions. Around three quarters of patients admitted to hospital with influenza had medical comorbidities, and of these, around 2% died in hospital.  

This year will be the second that a quadrivalent, rather than trivalent, vaccine is offered. It covers two A strains of influenza (Michigan and Hong Kong) and two B strains of influenza (Brisbane and Phuket). FluCAN researchers are yet to determine how comparatively effective the quadrivalent vaccines are.

The second study led by Professor Cheng set out to test reports that serial influenza vaccination had a negative impact of on vaccine protection. Previous studies had raised concerns about the recommendation for annual influenza vaccines, particularly for those at greatest risk.

It analysed data from 2010 to 2015: 6223 hospitalised influenza cases and 6505 controls who presented with influenza-test negative Acute Respiratory Illness.

In the six influenza seasons, vaccine effectiveness (VE) was estimated to be 43% overall. It was estimated to be 51% in those vaccinated in both the current and previous season, compared with 33% vaccinated in the current season only and 35% in the previous season only. 

The findings that vaccination in subsequent seasons was associated with a higher protection against hospitalisation with influenza than vaccination in either single season reinforced the current recommendations for annual influenza vaccination, particularly those at greatest risk of influenza disease, the study concluded.

References

Cheng AC, Holmes M, Dwyer DE, Irving LB, Korman TM, Senenayake S, Macartney KK, Blyth CC, Brown S, Waterer G, Hewer R, Friedman ND, Wark PA, Simpson G, Upham J, Bowler SD, Lessing A, Kotsimbos T, Kelly PM. Influenza epidemiology in patients admitted to sentinel Australian hospitals in 2015: the Influenza Complications Alert Network. Commun Dis Intell Q Rep. 2016 Dec 24;40(4):E521-E526.

Cheng AC, Macartney KK, Waterer GW, Kotsimbos T, Kelly PM, Blyth CC; FluCAN Investigators. Repeated vaccination does not appear to impact on influenza vaccine effectiveness against hospitalisation with confirmed influenza. Clin Infect Dis. 2017 Mar 17. doi: 10.1093/cid/cix209. [Epub ahead of print]
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