Healthy people who caught swine flu during the 2009 pandemic may have been protected against developing radiographically (x-ray) confirmed pneumonia by taking the antiviral drug oseltamivir (Tamiflu), concludes a study of cases in China published on bmj.com today.
The researchers also show that oseltamivir treatment was associated with shorter duration of fever and viral RNA shedding (the period when a virus is contagious), although they stress that their findings should be interpreted with caution.
In 2009, pandemic influenza A (H1N1) virus spread rapidly, resulting in millions of cases and over 18,000 deaths in over 200 countries.
Trials carried out on seasonal flu viruses have shown that taking antiviral drugs within 48 hours of symptom onset can reduce the severity and duration of symptoms, and possibly the risk of complications.
However, the extent to which antivirals may benefit otherwise healthy individuals with mild 2009 H1N1 infection, remains unknown.
So researchers reviewed the medical records of 1,291 patients in China with laboratory confirmed mild H1N1 infection during the 2009 pandemic.
The average age of patients was 20 years. Three quarters (76%) were treated with oseltamivir from a median of the third day of symptoms. Of 920 patients who had a chest x-ray, a minority (12%) had abnormal findings consistent with pneumonia.
No patients required intensive care unit admission or mechanical ventilation.
Using statistical modelling of the patients' data, the researchers ruled out the effects of age, sex, influenza vaccination, and treatment with antibiotics on the main study outcomes: getting pneumonia, having prolonged high fever, and viral RNA shedding. Oseltamivir treatment was then identified as a significant protective factor against subsequent development of pneumonia, confirmed by a chest x-ray. This protective effect was seen in all patients including those who started treatment more than two days after onset of symptoms.
Oseltamivir treatment started within two days of symptom onset also reduced the duration of fever and viral RNA shedding, they add. They also found that 2009 H1N1 might be shed longer than seasonal influenza virus.
These findings are consistent with patients with the 2009 H1N1 benefiting from use of oseltamivir, conclude the authors. However, they stress that their finding that oseltamivir treatment protected against subsequent radiographic pneumonia should be interpreted with caution, given the retrospective design of this work and the fact that not all patients underwent a chest x-ray.
They call for continued investigation into the effectiveness of antiviral treatment 'to allow for improvement both in clinical treatment and public health guidance.'