A genetically engineered version of the vaccinia virus has trebled the average survival time of people with a severe form of liver cancer, with only mild, flu-like side effects.

Thirty people with hepatocellular carcinoma received three doses of the modified virus – code-named JX-594 – directly into their liver tumour over one month. Half the volunteers received a low dose of the virus, the other half a high dose. Members of the low and high-dose groups subsequently survived for, on average, 6.7 and 14.1 months respectively. By contrast, trials several years ago showed that sorafenib, the best existing medication for this cancer, prolonged life by only three months.