The Australian experience of swine flu (or swine influenza A as it is currently known) has been much milder than anticipated. However, there is concern that this is just the dress rehearsal for a future, more deadly mutation of this particular virus.
In the Medical Journal of Australia’s online report this week ”Swine flu update: bringing home the bacon”, several characteristics of this virus have been observed:
– the symptoms have been milder than expected
– on average there is an incubation period of 3-4 days between exposure to the virus and onset of symptoms
– unlike most strains of influenza, the majority of people with swine flu do not experience a significant fever (in both mild and severe presentations of swine flu)
– in the US over a third of cases have diarrhoea and vomiting along with the usual symptoms such as a sore throat and malaise
– it is not as deadly – when the Mexican death rate is excluded from the statistics the mortality rate is 0.2% (including Mexico it brings it to 0.5%)
– older people may have some degree of immunity despite it being a new virus as there may be some viral similarity with a previous seasonal flu or flu vaccine, explaining why younger people have been more vulnerable to acquiring swine flu
The MJA published another piece this week, “Australia’s influenza containment plan and the swine flu epidemic in Victoria” examining the response to the Swine Flu at the epicentre of the Australian outbreak.
In reality, the severity of the 2009 swine flu outbreak has fallen well short of the worst-case scenario: instead of resulting in high mortality, swine flu has been associated with only a 1%–2% hospital admission rate and zero mortality in Australia (so far); early experience has shown that the clinical case definition (fundamental to accurate disease modelling) was not an accurate model for the swine flu epidemic…”
The article also made an alarming reference to our faith in current antiviral medication (oseltamivir, marketed as Tamiflu) and its efficacy. Other than the drug needing to be administered within 48 hours of the onset of the disease the authors noted, “it is known that the main seasonal influenza strain in the United States in 2008 was resistant to oseltamivir. The real nightmare scenario will be if the current swine flu strain also develops resistance in the face of widespread use of oseltamivir, leaving us with few treatment options. We are currently wasting oseltamivir on a mild illness when we are likely to need it next year, when the current strain could become more aggressive.”
And on that note a sub-type of the H1N1 virus has just been identified in Brazil. It is not known yet if this mutation of swine flu is any more virulent or is resistant to medication.