The Cochrane Collaboration claims to have unearthed evidence that the drug did not prevent the spread of flu or reduce dangerous complications and only slightly helped symptoms. It concluded that the drug reduced the persistence of symptoms of an Influenza infection from seven days to 6.3 days in adults and to 5.8 days in children. But the report's authors said drugs such as paracetamol could have a similar impact.
The new study used data from 46 trials (20 with oseltamivir and 26 with zanamivir) and found several problems in the design of many of those studies, which affected the confidence in their results.
On claims that the drug prevented complications such as pneumonia and other complications, like bronchitis, middle ear infection (otitis media) and sinusitis, developing, Cochrane suggested the trials were so poor there was "no visible effect". It also claimed that the drug had a number of underreported side-effects, including nausea, headaches, psychiatric events, kidney problems and hyperglycaemia.
However, the scientists fail to mention that Tamiflu may provide a slight survival advantage in the very ill. But the fact remains that antivirals like Tamiflu and Relenza cannot replace vaccination. It offers little benefit in the routine treatment of influenza in the otherwise-well individual, but may have a role in those with other medical conditions, or when used to prevent influenza’s spread.
It may not come as a surprise to you, but pharmaceutical companies, like Roche, disagree with the overall conclusions.
 Jefferson et al: Neuraminidase inhibitors for preventing and treating influenza in healthy adults and children in The Cochrane Library – 2014. Pdf of report is here.