Influenza Virus Subtypes
• Influenza A
• Influenza B
• Influenza C
Structure of influenza virus
Two surface antigens
Why influenza epidemics
• ‘Antigenic drift’
- Minor changes in
- No protection
(Karl G Nicholson, et al Lancet 2003; 362: 1733-45)
•Many subtypes (H and N)
•3 subtypes have caused
Avian Influenza (H5N1)
• 1st seen in 1997
• History of contact to dead/sick poultry
• Highly pathogenic
(Case Fatality Rate 60%)
• Most cases seen in children and adults
<40yrs, most deaths in 10-19 yr old.
cause high morbidity & mortality
A(H1N1) A(H2N2) A(H3N2)
“Hong Kong Flu”
20 - 40 m deaths 1 - 4 m deaths 1 - 4 m deaths
Credit: US National Museum of Health and Medicine
“Spanish Flu” “Asian Flu”
INFLUENZA PANDEMIC in the
PACIFIC ISLAND HISTORY - 1918
Some Pacific Islands amongst the worst affected:
1/3 to ½ of the pop. affected & ¼ died in some PICTs
Samoa (22% pop. Killed -7542 deaths),
Fiji (5% ~9000), Tonga (6%), Nauru (6%)
French Polynesia: Tahiti (25%) Guam (5%)
Others were totally spared:
American Samoa (strict maritime quarantine)
Kiribati, Tuvalu, Solomon Islands & Vanuatu (Australian
quarantine policy for outgoing steamships exclusively
servicing these islands)
• 1st wave generally mild
• Historically 2nd wave associated with
greater morbidity and mortality.
• Pandemics occur when a novel virus
infects a community
• As of 12 July lab confirmed cases in 214
WHO member states; 18337 deaths
• World wide pandemic activity is low.
Nasophaeyngeal swab to confirm
• Must be collected
within 3 days of onset
• Must have fever with
cough or sore throat.
Critical issues for Infection control
• Avoid crowding patients together, promote
distance between patients
• Protect mucosa of mouth and nose
• Perform hand hygiene
• Hand hygiene
• Respiratory hygiene/cough etiquette
• Avoid touching your face
• Environmental surfaces to be kept clean;
wipe with Sodium hypochlorite 1%
(Janola). Also hydrogen peroxide,
chlorine, detergents, iodine based
antiseptics and alcohols.
• Influenza can survive on environmental
Influenza Like Illness (ILI)
•Sudden onset of fever (38ºC or higher,
if no thermometer available, reported
chills or high temperature)
•At leas one of the following symptoms:
cough, sore throat, runny nose, nasal
congestion; in the absence of
Severe Acute Respiratory Illness
• Meets ILI case definition AND
• Shortness of breath or difficulty breathing
• Requiring hospital admission.
High risk group for severe disease
• 3rd trimester pregnancy, under 2yrs, 65+
yrs, diabetics, long term steroid therapy,
chronic lung and heart disease,
• Neurological disorders can increase risk of
severe disease in children.
• Large proportion of severe & fatal cases:
obese & morbidly obese, ye obesity hasn’t
been recognized as a risk factor.
• Majority have uncomplicated ILI, recovery
within a week, even with no medical Rx.
• Severe cases deteriorate about day 3 to 5
• Rapid deterioration, many progress to
respiratory failure within 24 hours – require
IMMEDIATE ICU admission.
• Oseltamivir (Tamiflu): used in cases with
high risk of severe disease
• Rx must be started early to reduce
disease severity & improve survival
chances, even without confirmatory test.
• Paracetamol, Vit. C, Increase fluid intake
• Most effective preventive tool
• May prove less effective if virus evolves
rapidly, and virus may get around growing
immunity in the population.
Must remain alert
• Second wave may or may not occur
• Pandemic continues, virus may evolve
without it being possible to predict when.