US health officials have launched an inquiry into a controversial study by scientists at Boston University who created an artificial form of Covid-19 in a laboratory.

The National Institutes of Health told the Financial Times its officials were investigating whether the study, which was partly funded by the US government, should have gone through extra checks before going ahead.

An early version of findings from the study, in which researchers combined a lab-made version of Covid-19’s original strain with the spike protein from the more transmissible Omicron variant, was published last Friday. Omicron has proved less deadly than the so-called “wild type” of the virus, but has spread far more quickly because it is better able to escape immune protection.