32 HOW TO TREAT : INFLUENZA
32 HOW TO TREAT : INFLUENZA
14 MARCH 2025 ausdoc . com . au
However , the impact of collective community-wide interventions to reduce influenza are demonstrated by the epidemiology of influenza during the COVID-19 pandemic . In Australia during 2020 and 2021 there was a marked decline in influenza , with the condition effectively absent from circulation from March 2020 to October 2021 because of a suite of interventions , including international travel restrictions and quarantine requirements . 52 Other measures enacted worldwide ( such as school and workplace closures , indoor restaurant dining restrictions , social distancing , face mask wearing , public event cancellations , and isolation and quarantine measures ) likely contributed to low influenza virus circulation . 16 For example in the WHO European Region there was a 99.8 % reduction in the number of specimens returning positive for influenza from October 2020 to February 2021 despite high levels of influenza testing . 52
Vaccines
Vaccination is known to be the most effective strategy for the prevention of influenza . The performance of influenza vaccines varies by year , vaccine formulation , and the underlying age , health condition , and prior virus and vaccine exposure of the recipient . The high rate of antigenic drift means that vaccines must be reformulated each year with the potential for imperfect matching between circulating influenza virus and vaccine strains . 53
The Department of Health and Aged Care recommends annual influenza vaccination for everyone six months or older .
Vaccination is particularly emphasised for those at risk of complications and severe disease ( see box 1 ) and those more likely to be at risk of influenza acquisition , or transmission of influenza to people at higher risk of complications such as healthcare workers , commercial poultry and pork industry workers and those travelling during influenza season . Two vaccination doses , four weeks apart , are recommended in children aged six months to nine years receiving influenza vaccine for the first time and people of any age receiving influenza vaccine for the first time after haematopoietic stem cell or solid organ transplant or CAR T-cell therapy . 53
Those aged six months to less than 65 years should receive a standard-dose egg-based or cell-based
How to Treat Quiz .
1 . Which THREE statements regarding influenza are correct ? a Influenza accounts for minor or major epidemics of seasonal influenza most years . b Seasonal epidemics typically occur during winter months in the Southern Hemisphere . c Influenza A viruses are the only influenza viruses known to cause global influenza pandemics . d Outbreaks usually begin abruptly , peaking over 6-7 weeks and lasting 3-5 months .
2 . Which TWO statements regarding the pathophysiology of influenza are correct ? a Influenza C is the most common cause of respiratory illness . b Humans are the primary reservoir for seasonal influenza . c Influenza A is a constantly evolving pathogen with a propensity for periodic antigenic variation . d Antigenic drift only occurs among influenza A viruses because of their extensive animal reservoirs .
3 . Which THREE statements regarding the transmission of influenza are correct ? a Influenza virus spreads primarily via person-to-person respiratory transmission . b In immunocompetent hosts viral shedding peaks at 48-72 hours and then swiftly declines . influenza vaccine , while those 65 or older should receive adjuvanted or high-dose influenza vaccine ; they may receive standard-dose eggbased or cell-based influenza vaccine if the adjuvanted or high-dose vaccine is unavailable . 53
While influenza vaccine is not approved for infants younger than six months , prevention strategies in this group include vaccination of pregnant women , household contacts six months or older , and caregivers . Vaccinating pregnant women reduces the risks and complications
The high rate of antigenic drift means that vaccines must be reformulated each year . associated with severe influenza in their infants for the first six months because of transplacental transfer of influenza-specific antibodies . Influenza vaccine is safe in pregnant and breastfeeding women . 53
In most of Australia influenza usually peaks between June and September . Annual influenza vaccination is recommended before the influenza season starts , with protection expected to last the whole season , but optimal protection occurs within 3-4 months after vaccination . Late-season vaccination can be
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c The typical incubation period ( time between exposure and the appearance of first symptoms ) ranges from 1-4 days . d Viral shedding may be prolonged , lasting weeks to months , in immunocompromised patients .
4 . Which THREE may be features on presentation in extremes of age and immunocompromise ? a Altered mental status in older adults . b Fever in all patients . c Gastrointestinal complaints in children . d Non-specific , such as anorexia , malaise , weakness , or dizziness .
5 . Which THREE statements regarding the sequelae and complications of influenza are correct ? a Weakness or fatigue may last several weeks . b Serious complications of influenza are common . c Even those with a regular exercise routine such as runners may have reduced performance for a month or more . d In the elderly there is often a temporary decline in baseline activity and loss of appetite .
6 . Which ONE is the common cause of secondary bacterial pneumonia in influenza ? a Staphylococcus aureus . b Streptococcus pneumoniae . c Pseudomonas aeruginosa . d Haemophilus influenzae .
7 . Which TWO statements regarding the diagnosis of influenza are correct ? a When influenza viruses are the predominant respiratory viruses in the community , clinical diagnosis of uncomplicated infection is usually reliable . b Vaccinated patients do not get influenza . c The most useful test for the diagnosis of influenza is serological testing . d A positive test result for influenza alone does not rule out SARS-CoV-2 co-infection when both viruses are present in the community .
8 . Which THREE statements regarding the management of influenza are correct ? a Prescribe antiviral therapy to all patients with influenza . b The potential adverse effects of neuraminidase inhibitors include nausea , vomiting ,
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• RACGP points are uploaded every six weeks and ACRRM points quarterly . beneficial as influenza can circulate year-round . In particular , pregnant women and travellers can benefit from vaccination at any time of the year . 53
Vaccine-associated adverse events are usually mild and self-limiting ; the most common is injection site reactions with pain at the site for about two days . Less commonly fever , myalgia and malaise may occur and last 1-2 days . 7 , 53
In 1976 , a specific formulation of influenza vaccine was linked to an increased risk of GBS . Surveillance has since shown that GBS occurs at a low rate of about one case per million doses of influenza vaccine . In comparison , the risk of GBS following influenza is estimated to be nearly 15 times the risk of GBS following influenza vaccine ; thus , vaccination may reduce the overall risk of GBS by preventing influenza .
54 , 55
People with egg allergy , including anaphylaxis , can safely be vaccinated with any influenza vaccines ( including egg- and cell-based vaccines ) unless they have reported a serious adverse reaction to influenza vaccines . Egg-based vaccines may contain traces of egg-derived protein ( ovalbumin ), at less than 1μg of ovalbumin per dose . Most people with an egg allergy , including anaphylaxis , can safely receive influenza vaccines that contain less than 1μg of ovalbumin per dose . A 2012 review
INFLUENZA
headaches and neuropsychiatric events . c Oseltamivir is considered safe during pregnancy and breastfeeding . d Avoid aspirin in those with suspected or confirmed influenza because of the association between aspirin and the risk of Reye ’ s syndrome .
9 . Which THREE statements regarding antivirals in influenza are correct ? a Zanamivir is the first-line choice in patients with asthma . b Greatest clinical benefit occurs when antiviral treatment is started close to illness onset . c Resistance to baloxavir may emerge during treatment . d Rare serious skin reactions may occur with peramivir , zanamivir and oseltamivir .
10 . Which TWO statements regarding influenza prevention are correct ? a Collective community-wide behavioural interventions do reduce influenza . b Vaccination is known to be the most effective strategy for the prevention of influenza . c Influenza vaccine is contraindicated in pregnant and breastfeeding women . d Vaccination with an egg-based vaccine is contraindicated in all people with an egg allergy . of published studies including 4172 egg-allergic patients , of whom 513 reported a history of severe allergic reaction , found no cases of anaphylaxis after receiving an inactivated
53 , 56 , 57 influenza vaccine .
THE FUTURE
ONGOING research and development in pursuit of a universal influenza vaccine is underway . Key methodologies include induction of broadly neutralising antibodies that recognise less antigenically variable regions on the stalk of the haemagglutinin and use of mRNA technology to induce an immune response against all known
58 , 59 influenza virus subtypes .
CASE STUDY
ERIC , a 60-year-old male , presents to his GP complaining of a 12-hour history of fevers and cough . This is in the context of a recent exposure to his unwell granddaughter whose childcare facility has had recent cases of confirmed influenza . His SARS - CoV-2 rapid antigen test is negative .
His history is remarkable only for mild asthma , and he receives an annual influenza vaccination . Eric reports his partner has recently returned home after a renal transplant .
Given his history of asthma and potential for influenza transmission to a high-risk partner , Eric is provided with a treatment course of oseltamivir . In conjunction with his renal physician , his partner is provided a course of prophylactic oseltamivir . PCR testing performed on the day of presentation subsequently returns positive for influenza A .
Antiviral medication can reduce the severity and duration of influenza and reduce the risk of transmission . Advise contacts at high risk of developing severe disease to seek medical advice on prophylaxis and early medical review if symptoms develop .
CONCLUSION
Influenza is a constantly evolving pathogen and a major cause of morbidity and mortality in Australia . GPs play a vital role in influenza , seeing on average 300,000 seasonal influenza consultations in Australia each year . While most people with influenza recover without serious complications or sequelae , specific groups are at higher risk of poor outcomes ; those 65 or older , pregnant women , young children and the immunosuppressed . GPs play an important part in recognising those most at risk of poor outcomes especially where prompt diagnosis can facilitate early antiviral treatment that provides the greatest clinical benefit . Vaccination is the most effective strategy for the prevention of influenza and annual vaccination is recommended for those aged six months or older .
RESOURCES
• Influenza . In : Therapeutic Guidelines Antibiotic . Therapeutic Guidelines Limited , Melbourne , April 2019 ( Amended June 2019 ).
• Australian Immunisation Handbook — Influenza bit . ly / 41Cm4XO
References Available on request from howtotreat @ adg . com . au