Influenza and antiviral treatment: Viva

Branch 1: Recognising influenza and triaging severity

The candidate should recognise the classic picture of influenza in an older child: the abrupt onset — within hours of appearing well — of high fever, dry cough, sore throat, myalgia and marked fatigue, against a background of community influenza activity. The suddenness is the clue that distinguishes influenza from the gradual, predominantly coryzal common cold, and the classroom cluster raises the pre-test probability in season. [2]

The candidate should then triage severity and risk. This child is alert and cardiovascularly stable with acceptable oxygenation, placing him in the non-severe category, but the candidate must state explicitly the features that would escalate management: respiratory distress or hypoxia, dehydration or poor feeding, altered consciousness or seizures suggesting encephalopathy, tachycardia out of proportion to fever or poor perfusion suggesting myocarditis, and a biphasic deterioration suggesting secondary bacterial pneumonia. The candidate should also establish the host risk profile — age under two, chronic lung, cardiac or neurologic disease, immunocompromise, long-term aspirin — because high-risk status lowers the threshold to treat. [2]

The examiner will probe the atypical infant presentation. The candidate should explain that an infant under two may have no localising respiratory story at all: fever, poor feeding, irritability, lethargy, apnoea or a sepsis-like picture can be the whole illness, and that influenza belongs in the differential of the unwell infant alongside bronchiolitis, sepsis and urinary infection. A low threshold to test and treat in season is what prevents the catastrophic miss. [2]

Branch 2: Testing, and the decision to treat

The examiner pivots to investigation and treatment. The candidate should describe a nasopharyngeal swab or aspirate for influenza PCR — often as part of a respiratory-virus panel — as the confirmatory test, and should caution that rapid antigen tests have lower sensitivity, so a negative rapid test in a sick child does not exclude influenza and must not withhold antivirals. The principle is that a sick child should never wait for the PCR result before starting antivirals. [2]

For this well, low-risk older child seen within 12 hours of onset, the candidate should weigh the benefit of antivirals against the modest symptom reduction. Treating within 48 hours can shorten illness and reduce household transmission, and is a reasonable shared decision when the family is keen. The candidate should contrast this with the rule for high-risk and hospitalised children — those under two, with chronic conditions, or severe disease — in whom oseltamivir is started empirically regardless of the duration of symptoms, because severity, not the clock, drives treatment. [1]

The examiner will probe the antivirals. Oseltamivir is first-line: a five-day oral course dose-adjusted for weight and age, with the landmark trial showing it shortened illness and reduced acute otitis media in children, and pharmacokinetic work establishing safe dosing even in neonates. Baloxavir marboxil is a single-dose oral option that works one step earlier, blocking the viral cap-dependent endonuclease rather than virion release; its pivotal trial showed faster reduction in viral shedding. The candidate should place baloxavir as an option in eligible older children and adolescents while keeping oseltamivir as the evidence anchor for severe disease and the youngest infants. [3]

Branch 3: The biphasic deterioration

The examiner may pivot: the child is sent home with oseltamivir and safety-netting, but returns on day four with a new fever, worsening breathlessness and looking septic. The candidate must now recognise the classic biphasic course of secondary bacterial pneumonia and abandon the reassurance of an uncomplicated illness. [2]

The candidate should state that secondary bacterial pneumonia — most often Staphylococcus aureus including methicillin-resistant strains, Streptococcus pneumoniae and Haemophilus influenzae — is a leading cause of influenza death, and that a new fever with worsening breathlessness after initial improvement warrants empirical antibiotics covering these organisms immediately, alongside ongoing supportive care and completion of the oseltamivir course. The candidate should emphasise that recognising this biphasic course and treating it early is one of the few things that genuinely changes the outcome of severe influenza. [2]

Finally the candidate should close the loop with prevention. The clinical encounter does not end when the child improves; it ends when the contacts are protected and the family is vaccinated. The candidate should describe the annual inactivated influenza vaccine from six months (two doses in the first season under nine years), maternal vaccination in pregnancy to protect the newborn, household vaccination to protect the infant too young to be fully covered, and post-exposure prophylaxis for high-risk contacts. A clear explanation that prevention is the backbone of influenza control demonstrates the understanding that examiners are testing. [1]