Influenza nursing: assessment, interventions, and NCLEX review

Influenza is an acute respiratory illness caused by influenza A or B viruses that infects millions of Americans each season and kills tens of thousands. During the 2022–2023 influenza season, the CDC estimated 26–50 million illnesses, 290,000–650,000 hospitalizations, and 19,000–58,000 deaths in the United States. For nursing students, influenza is an NCLEX-guaranteed topic that spans pharmacology (antivirals must start within 48 hours), infection control (droplet precautions with specific airborne upgrade scenarios), high-risk population management, and recognition of life-threatening complications including primary viral pneumonia, secondary bacterial pneumonia, ARDS, and septic shock.

This reference covers pathophysiology, symptom recognition, comparison with common mimics, nursing assessment priorities, interventions by body system, antiviral therapy, transmission and isolation, high-risk populations, complications, prevention, and six NCLEX-style practice questions. Use alongside the pneumonia nursing reference for lower respiratory complication management, the ARDS nursing reference for severe respiratory failure, the sepsis nursing reference for secondary bacterial sepsis, the MRSA nursing reference for post-influenza staphylococcal pneumonia, and the COVID-19 nursing reference for airborne respiratory viral illness comparison.

Influenza at a glance

Pathophysiology

Viral structure and the significance of antigenic variation

Influenza viruses are enveloped, negative-sense single-stranded RNA viruses in the Orthomyxoviridae family. The two surface glycoproteins — hemagglutinin (HA) and neuraminidase (NA) — are central to pathogenesis, diagnosis, immunity, and antiviral targeting.

Hemagglutinin mediates viral attachment to sialic acid receptors on respiratory epithelial cells and is the primary target of the host’s neutralizing antibody response. Human influenza viruses preferentially bind alpha-2,6-linked sialic acid receptors located in the upper respiratory tract (nose, throat, trachea). Avian influenza viruses preferentially bind alpha-2,3-linked receptors found deeper in the lower respiratory tract — which partly explains why human-to-human transmission is inefficient for most avian strains but why those that do infect humans tend to cause severe lower respiratory disease.

Neuraminidase cleaves sialic acid linkages, releasing newly assembled viral particles from infected cells and enabling spread to adjacent epithelium. Neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) exploit this mechanism — by blocking neuraminidase, they trap new viral particles at the cell surface and prevent infection spread.

Antigenic drift and antigenic shift

Two processes drive the perpetual mismatch between circulating influenza viruses and existing immunity:

Antigenic drift is the accumulation of point mutations in the HA and NA genes as the virus replicates. RNA polymerase lacks proofreading ability, so errors accumulate continuously. This gradual change is why influenza vaccines must be reformulated annually — last year’s antibodies may not fully neutralize this year’s circulating strains.

Antigenic shift is a sudden, major change in HA or NA that occurs when two different influenza A strains co-infect the same cell and exchange genomic segments (reassortment). The result is a novel subtype for which most humans have little or no pre-existing immunity — the conditions for pandemic influenza. The 2009 H1N1 pandemic resulted from a reassortment event combining human, avian, and swine influenza genes. Influenza B does not undergo antigenic shift because it has no animal reservoir, which is why influenza A has pandemic potential and influenza B does not.

Viral replication and mucosal injury

Once hemagglutinin binds sialic acid receptors, the virus is internalized via endocytosis. Inside the endosome, low pH triggers conformational changes that fuse the viral envelope with the endosomal membrane, releasing the viral RNA into the cytoplasm. The RNA travels to the nucleus, where viral RNA polymerase transcribes viral genes. Newly assembled virions bud from the cell surface — aided by neuraminidase — to infect neighboring cells.

The respiratory epithelium responds to infection with local inflammation. Infected cells release cytokines and chemokines — including IL-6, TNF-alpha, IFN-alpha, and IFN-beta — that recruit innate immune cells and produce the systemic symptoms of fever, myalgia, and malaise. The respiratory epithelium itself is damaged and denuded, impairing mucociliary clearance and creating a substrate for secondary bacterial invasion.

Cytokine storm

In severe influenza — particularly with novel pandemic strains like H5N1 and the 2009 H1N1 — an exaggerated, dysregulated immune response amplifies tissue injury beyond what the virus alone causes. This cytokine storm produces capillary leak, diffuse alveolar damage, and progression to acute respiratory distress syndrome (ARDS). Cytokine storm is most prominent in young adults with intact immune systems (which partly explains the W-shaped mortality curve of the 1918 pandemic, where 20–40-year-olds had the highest death rates) and in immunocompromised patients who cannot control viral replication. See the ARDS nursing reference for management of respiratory failure in this setting.

Clinical presentation

Symptom onset and pattern

Influenza is characterized by the abrupt onset of systemic symptoms — patients often describe knowing the exact hour they became ill. This distinguishes influenza from rhinovirus (common cold), which begins gradually.

Classic presentation:

• Fever — typically 38°C–40°C (100.4°F–104°F), often with rigors (shaking chills)
• Prominent myalgia — described as severe muscle aches, especially in back, legs, and arms
• Headache — often severe, frontal or retro-orbital
• Fatigue and malaise — profound, frequently described as inability to get out of bed
• Dry cough — present in most cases, initially non-productive
• Nasal congestion and rhinorrhea — less prominent than in common cold
• Sore throat

Fever typically peaks in the first 24–48 hours and resolves by day 3–5 in uncomplicated cases. Cough and fatigue may persist for 1–2 weeks after fever resolution. Gastrointestinal symptoms (nausea, vomiting, diarrhea) occur more commonly in children and with certain strains.

Flu vs cold vs COVID-19: comparison table

Diagnosis

Rapid influenza diagnostic tests (RIDTs)

RIDTs are immunoassay-based point-of-care tests that detect influenza A and B antigens from nasopharyngeal swabs. Results are available in 10–15 minutes, making them useful for rapid clinical decision-making in the ED and urgent care settings.

Key nursing knowledge about RIDTs:

• Sensitivity: 50–70% (moderate) — a negative RIDT does NOT rule out influenza, particularly early in illness or in high clinical suspicion cases
• Specificity: 90–99% — a positive RIDT is highly reliable
• During peak influenza season, clinical diagnosis may be more reliable than RIDTs given the low pre-test probability of false positives and the risk of false-negative RIDTs
• Newer digital immunoassay RIDTs have improved sensitivity (80–90%) and are now available in many hospitals

Reverse transcription PCR (RT-PCR)

RT-PCR is the gold standard for influenza diagnosis. It detects viral RNA with high sensitivity (90–99%) and specificity, distinguishes influenza A from B, and can subtype influenza A (important for identifying novel strains). Nasopharyngeal swab is the preferred specimen. Results typically take 1–4 hours with rapid PCR platforms. RT-PCR is indicated when RIDTs are negative but clinical suspicion remains high, when novel influenza is suspected, or for hospitalized patients.

Clinical diagnosis

During known influenza outbreaks or peak flu season, the combination of abrupt fever + cough + myalgia has a positive predictive value of approximately 79–85% for influenza in adults presenting with influenza-like illness (ILI). Clinical diagnosis is acceptable when testing resources are limited; antiviral therapy should not be delayed for test results in high-risk hospitalized patients.

Nursing assessment

Systematic nursing assessment for suspected influenza focuses on respiratory compromise, fluid status, and identification of high-risk features that signal potential deterioration.

Respiratory status

• Auscultate lungs — note presence of crackles (suggests developing pneumonia), wheezing, or decreased breath sounds
• Measure SpO2 by pulse oximetry — SpO2 <94% warrants escalation; <90% is an emergency
• Assess respiratory rate and work of breathing — tachypnea (RR >20), use of accessory muscles, intercostal retractions, or nasal flaring indicate respiratory distress
• Monitor for cyanosis (central cyanosis — lips, tongue — is more reliable than peripheral)

Vital sign pattern

• Temperature — document pattern and height of fever; rigors suggest rapid rise
• Heart rate — tachycardia is expected with fever (approximately 10 bpm per 1°C rise); persistent tachycardia after fever resolution warrants investigation
• Blood pressure — hypotension is not expected in uncomplicated influenza; presence should prompt sepsis workup
• Respiratory rate — the single most sensitive vital sign for respiratory deterioration; refer to vital signs by age reference for pediatric normal ranges

Fluid and nutritional status

• Assess skin turgor, mucous membrane moisture, urine output (goal ≥0.5 mL/kg/hr)
• Fever increases insensible fluid losses by approximately 100–150 mL per day per degree above normal
• Children and elderly patients are at highest risk for dehydration; monitor more frequently
• Review intake and output every shift

High-risk feature identification

Identify patients requiring closer monitoring or early antiviral therapy regardless of symptom duration:

• Age ≥65 years or children <2 years
• Pregnancy or within 2 weeks postpartum
• BMI ≥40
• Chronic pulmonary disease (asthma, COPD), cardiovascular disease, renal disease, hepatic disease, neurologic disease
• Immunosuppression (HIV, transplant recipients, chemotherapy)
• Residents of long-term care facilities

Nursing interventions

Pharmacological management

Neuraminidase inhibitors

Oseltamivir (Tamiflu) is the most widely used antiviral for influenza. It is an oral neuraminidase inhibitor that reduces illness duration by approximately 1 day in otherwise healthy adults, and reduces hospitalization rates, complications, and mortality in high-risk populations when started promptly.

Critical timing: Oseltamivir must be started within 48 hours of symptom onset to provide maximum benefit in outpatient treatment. In hospitalized patients with severe influenza or high-risk features, antiviral treatment should be started regardless of time since symptom onset — benefit has been demonstrated even when started 4–5 days after onset in severely ill patients.

Dosing:

• Adults: 75 mg orally twice daily × 5 days (treatment); 75 mg once daily × 10 days post-exposure (prophylaxis)
• Renal dose adjustment required for creatinine clearance <30 mL/min
• Available as capsules and oral suspension; may be administered via NG tube in ICU patients

Nursing considerations:

• Administer with food to reduce GI side effects (nausea, vomiting)
• Monitor for neuropsychiatric side effects (confusion, hallucinations, self-harm behaviors) — rare but reported, particularly in adolescents; FDA labeling includes a warning
• Do NOT stop antiviral therapy early if symptoms persist — complete the full 5-day course
• Educate patients: oseltamivir is not a substitute for annual vaccination

Zanamivir (Relenza) is an inhaled neuraminidase inhibitor delivered via a breath-activated inhaler. It achieves high local respiratory tract concentrations with minimal systemic absorption.

Contraindicated in: Asthma and COPD — zanamivir can trigger bronchospasm due to the lactose carrier in the inhaler formulation. This is a frequently tested NCLEX pharmacology contraindication.

Baloxavir marboxil (Xofluza) is a cap-dependent endonuclease inhibitor with a novel mechanism of action (different from neuraminidase inhibitors). It is given as a single oral dose, offers activity against oseltamivir-resistant strains, and was approved by the FDA in 2018. It is indicated for uncomplicated influenza in adults and adolescents ≥12 years within 48 hours of symptom onset.

Antiviral comparison table

Transmission and isolation precautions

Transmission routes

Influenza spreads primarily via respiratory droplets (particles >5 microns in diameter) generated when an infected person coughs, sneezes, speaks, or breathes. These droplets travel up to 6 feet and are inhaled by susceptible individuals or deposited on mucous membranes.

Contact transmission also occurs — influenza virus survives on hard surfaces for 24–48 hours. Touching a contaminated surface and then touching the mouth, nose, or eyes is an important transmission route, particularly in household and healthcare settings.

Airborne transmission of smaller aerosol particles (≤5 microns) is possible but plays a minor role in typical settings. However, aerosol-generating procedures (AGPs) — intubation, bronchoscopy, suctioning, CPR, nebulized medication administration — significantly increase aerosol production and require upgraded precautions.

Standard droplet precautions for influenza

• Private room or cohort patients with confirmed influenza; close door when possible
• Surgical mask worn by all staff entering within 6 feet of the patient
• Eye protection (goggles or face shield) when splashes are anticipated
• Hand hygiene before and after all patient contact — soap and water preferred when hands are visibly soiled or contaminated; alcohol-based hand rub is acceptable for routine decontamination
• Patient transport: patient wears surgical mask when outside room; minimize transport; notify receiving areas in advance
• Precautions maintained for 7 days from illness onset or 24 hours after resolution of fever and respiratory symptoms, whichever is longer; for immunocompromised patients, maintain precautions for the duration of illness

Upgrading to airborne precautions

For all aerosol-generating procedures, apply:

• N95 respirator (or higher) — must be fit-tested per OSHA requirements
• Gown and gloves (contact precautions component)
• Eye protection
• Procedure performed in a negative-pressure room when available

Nurses must distinguish this from TB, which requires airborne precautions at all times (not only during procedures). See the TB nursing reference for comparison of respiratory isolation levels.

High-risk populations

Certain populations face disproportionate risk of severe influenza, complications, and death. Nurses must identify these patients early and prioritize antiviral treatment, closer monitoring, and escalation planning.

Complications

Primary influenza pneumonia

Primary influenza pneumonia occurs when the virus directly invades the lower respiratory tract, causing diffuse alveolar damage and bilateral interstitial infiltrates on chest X-ray. It is less common than secondary bacterial pneumonia but clinically severe, progressing rapidly from typical influenza to respiratory failure over 24–48 hours. Risk is highest in patients with pre-existing cardiac disease (particularly mitral stenosis) and immunocompromised individuals.

Clinical features that distinguish primary influenza pneumonia from uncomplicated influenza: persistent or worsening fever beyond day 3, progressive dyspnea, SpO2 decline, bilateral infiltrates on imaging. Management requires oxygen supplementation, antiviral therapy (oseltamivir regardless of time since onset), and ICU-level respiratory support for patients progressing to ARDS. See the pneumonia nursing reference for comprehensive respiratory management.

Secondary bacterial pneumonia

Secondary bacterial pneumonia is more common than primary viral pneumonia and typically presents 5–7 days after initial influenza illness — after the patient appeared to be improving. The mechanism is impaired mucociliary defense, epithelial denudation, and altered innate immunity from the initial viral infection, creating a permissive environment for bacterial superinfection.

Key pathogens:

• Streptococcus pneumoniae — most common bacterial cause of post-influenza pneumonia
• Staphylococcus aureus (including MRSA) — associated with necrotizing pneumonia; produces rapid, severe deterioration; mortality is high. Post-influenza MRSA pneumonia is a key clinical scenario — see the MRSA nursing reference for management
• Haemophilus influenzae — particularly in patients with underlying pulmonary disease
• Group A Streptococcus

Clinical presentation: Recurrence of fever after initial improvement; new productive (purulent) cough; new or worsening infiltrate on chest X-ray; rising WBC count. Refer to the nursing lab values cheat sheet for WBC interpretation.

Secondary bacterial pneumonia that progresses to bacteremia can cause septic shock. See the sepsis nursing reference for sepsis management.

ARDS (acute respiratory distress syndrome)

ARDS is the most severe complication of influenza-related respiratory disease. It results from cytokine storm causing diffuse alveolar damage, capillary leak, and refractory hypoxemia. The Berlin definition requires: onset within 1 week of a known insult, bilateral infiltrates on imaging, PaO2/FiO2 ≤300 mmHg, and absence of cardiogenic edema as primary cause.

Nursing management of influenza-associated ARDS requires ICU-level care: lung-protective ventilation (tidal volume 6 mL/kg ideal body weight, plateau pressure ≤30 cmH2O), prone positioning, PEEP optimization, and hemodynamic support. See the ARDS nursing reference for detailed management.

Myocarditis and cardiac complications

Influenza can cause direct viral myocarditis and cardiac arrhythmias. Epidemiological studies demonstrate a 6-fold increase in acute myocardial infarction risk in the week following influenza diagnosis — attributed to plaque destabilization from systemic inflammation. Nursing assessment should include monitoring for new chest pain, palpitations, or ECG changes in hospitalized influenza patients, particularly those with known cardiovascular disease.

Encephalitis and neurologic complications

Influenza-associated encephalitis/encephalopathy (IAE) is rare but potentially fatal. It most commonly occurs in children. Symptoms include altered mental status, seizures, and focal neurologic deficits developing during or shortly after influenza illness. It is distinct from febrile seizures, which are benign. Nursing priorities: monitor mental status in febrile children; avoid aspirin in children (see Reye’s syndrome below).

Reye’s syndrome

Reye’s syndrome is a rare but life-threatening condition characterized by acute non-inflammatory encephalopathy and hepatic dysfunction, occurring almost exclusively in children and adolescents who receive aspirin during a viral illness (influenza or varicella). The mechanism involves aspirin disrupting mitochondrial beta-oxidation in the context of viral infection. Since widespread awareness and aspirin avoidance recommendations were adopted in the 1980s, Reye’s syndrome has become rare in the United States.

Nursing implication: NEVER administer aspirin or aspirin-containing products (Pepto-Bismol contains bismuth subsalicylate) to patients ≤18 years with influenza. Use acetaminophen or ibuprofen for fever and pain management.

Septic shock

Progression from secondary bacterial pneumonia to bacteremia and septic shock represents the most common cause of influenza-related ICU admission and death. Early recognition using sepsis screening criteria (qSOFA, SOFA) is essential. See the sepsis nursing reference for complete management.

Prevention

Annual influenza vaccination

The single most effective preventive measure against influenza is annual vaccination. Annual vaccination is recommended by the CDC for all persons aged 6 months and older in the United States, with rare exceptions. Vaccination should ideally occur before the end of October (when influenza activity typically begins), but vaccination at any time during the season provides benefit.

Vaccine types

Vaccine effectiveness and herd immunity

Influenza vaccine effectiveness varies by season (typically 40–60%) depending on how well the vaccine strains match circulating viruses. Even imperfect vaccines reduce severity, complications, and death, particularly in high-risk groups. Vaccination of healthcare workers and household contacts reduces transmission to vulnerable patients who cannot mount adequate vaccine responses — the herd immunity principle.

Nursing education points: Patients frequently believe the influenza vaccine can cause influenza. It cannot — IIV contains inactivated virus (no live virus), and LAIV is attenuated to replicate only in the cooler nasal epithelium, not in the lower respiratory tract. Post-vaccination arm soreness, low-grade fever, and mild myalgia in the first 24–48 hours are normal immune responses, not influenza illness.

Non-pharmacologic prevention

Hand hygiene (soap and water for ≥20 seconds, or alcohol-based hand rub with ≥60% alcohol) is the most important non-vaccine preventive measure. Respiratory etiquette (cover coughs and sneezes with elbow, not hands), avoiding touching face with unwashed hands, and staying home when ill all reduce community spread.

NCLEX-style practice questions

Question 1

A nurse is caring for a 72-year-old patient admitted with influenza A. The patient’s oxygen saturation is 91% on room air, respiratory rate is 24 breaths/minute, and temperature is 39.2°C. Which nursing action has the highest priority?

A. Administer acetaminophen to reduce fever B. Apply supplemental oxygen and notify the provider C. Initiate droplet precautions and place a surgical mask on the patient D. Encourage oral fluid intake and reposition to semi-Fowler’s

Correct answer: B

Rationale: The priority concern is impaired gas exchange — SpO2 of 91% is below the acceptable threshold of ≥94%, and the elevated respiratory rate indicates respiratory distress. Applying supplemental oxygen and notifying the provider addresses the immediate life-threatening priority. While fever management (A) and fluid encouragement (D) are important, hypoxemia is the emergent concern. Droplet precautions (C) should already be in place and are not the priority action at this moment.

Question 2

A nurse is preparing to administer oseltamivir (Tamiflu) to a patient with confirmed influenza. The patient states, “I’ve been sick for 4 days — will this still help me?” Which response is most accurate?

A. “Oseltamivir is most effective within the first 48 hours, but you should still receive it because you are hospitalized.” B. “Since it’s been more than 48 hours, the medication is unlikely to help at this point.” C. “Oseltamivir works at any point in the illness and will provide full benefit.” D. “We will need to check a viral load before deciding whether to continue the medication.”

Correct answer: A

Rationale: The 48-hour window is the threshold for maximum benefit in outpatient, otherwise healthy adults. However, in hospitalized patients and those with high-risk conditions, antivirals should be administered regardless of the time since symptom onset — clinical benefit has been demonstrated even when started later. Option B is incorrect in the context of a hospitalized patient. Option C overstates the benefit — the window does matter for optimal efficacy. Option D is incorrect — influenza viral loads are not routinely used to guide antiviral decisions in clinical practice.

Question 3

A nurse is reviewing medication orders for a 14-year-old with influenza and high fever. Which medication, if ordered, should the nurse question?

A. Acetaminophen 650 mg orally every 6 hours B. Ibuprofen 400 mg orally every 8 hours C. Aspirin 325 mg orally every 4 hours D. Oseltamivir 75 mg orally twice daily for 5 days

Correct answer: C

Rationale: Aspirin is contraindicated in children and adolescents (≤18 years) with influenza due to the risk of Reye’s syndrome — a rare but life-threatening condition causing acute encephalopathy and hepatic failure. Acetaminophen (A) and ibuprofen (B) are both appropriate analgesic/antipyretic choices in this age group. Oseltamivir (D) is indicated and appropriate for influenza treatment in a 14-year-old.

Question 4

A nurse is preparing a patient with asthma for discharge with a prescription for zanamivir (Relenza) for influenza treatment. What is the priority nursing action?

A. Instruct the patient to use the Diskhaler device with each dose B. Notify the provider and clarify the order — zanamivir is contraindicated in asthma C. Teach the patient to take zanamivir with food to reduce GI side effects D. Inform the patient that zanamivir provides maximum benefit if started within 48 hours

Correct answer: B

Rationale: Zanamivir is contraindicated in patients with asthma or COPD because the lactose carrier in the inhaler formulation can trigger severe bronchospasm, which may be life-threatening. The nurse has a responsibility to clarify this order with the prescriber before administration. Oseltamivir should be prescribed instead for patients with reactive airway disease. Options A and D are accurate statements about zanamivir but do not address the safety concern. Option C is incorrect — zanamivir is inhaled, not oral; GI concerns are irrelevant.

Question 5

A nurse is implementing droplet precautions for a patient with influenza. Which action requires correction?

A. Placing a surgical mask on the patient when transporting to radiology B. Wearing a surgical mask upon entering the patient’s room C. Applying an N95 respirator when performing nasotracheal suctioning D. Discontinuing precautions 24 hours after the patient’s temperature normalizes without antipyretics

Correct answer: D

Rationale: Droplet precautions for influenza should be maintained for 7 days from illness onset OR until 24 hours after fever and respiratory symptoms resolve without antipyretics — whichever is longer. Simply waiting 24 hours after temperature normalization without considering the 7-day minimum may allow premature discontinuation. Options A (patient wears mask for transport), B (surgical mask within 6 feet), and C (N95 for aerosol-generating procedures) are all correct infection control practices.

Question 6

A patient recovering from influenza develops a new fever of 39.8°C, productive cough with yellow-green sputum, and chest pain on day 7 of illness — after having improved on days 4–6. Which complication does the nurse recognize?

A. Primary influenza pneumonia B. Secondary bacterial pneumonia C. Influenza-associated encephalitis D. Cytokine storm syndrome

Correct answer: B

Rationale: The biphasic illness course — initial influenza illness, apparent improvement, followed by worsening symptoms with purulent sputum — is the classic presentation of secondary bacterial pneumonia. This complication typically occurs 5–7 days after initial influenza onset when damaged respiratory epithelium becomes colonized by bacteria such as Streptococcus pneumoniae or Staphylococcus aureus (including MRSA). Primary influenza pneumonia (A) occurs during, not after, the initial illness and presents with progressive hypoxemia rather than this pattern. Encephalitis (C) presents with neurologic symptoms, not purulent pulmonary findings. Cytokine storm (D) would have been evident early in the illness course with rapid hemodynamic deterioration.

Related references

• RSV nursing reference — RSV and influenza co-circulate October–March and can be clinically similar. This guide covers RSV bronchiolitis, high-flow nasal cannula, nirsevimab prophylaxis, and NCLEX-tested distinctions between the two viruses.
• Pneumonia nursing reference — influenza is a major cause of both primary viral pneumonia and secondary bacterial pneumonia. Covers CAP vs HAP classification, CURB-65 scoring, and antibiotic selection.
• ARDS nursing reference — severe influenza with cytokine storm can progress to ARDS. Covers lung-protective ventilation and prone positioning.
• Sepsis nursing reference — secondary bacterial pneumonia after influenza can trigger sepsis. Covers SIRS criteria, qSOFA, and the hour-1 bundle.
• COVID-19 nursing reference — compare airborne respiratory viral illness, including isolation precaution differences and antiviral strategies.

Sources: CDC Influenza Information (2023–2024 season); ACIP Influenza Vaccine Recommendations (MMWR 2023); IDSA Clinical Practice Guidelines for Influenza (Uyeki et al., 2019); FDA prescribing information — oseltamivir, zanamivir, baloxavir; Guidance for the Prevention and Control of Influenza in the Peri- and Postpartum Settings; Hayden FG and Shindo N. Influenza virus polymerase inhibitors in clinical development. Curr Opin Infect Dis. 2019.