China's CanSino Biologics Inc said on Wednesday that no serious blood clot cases had been reported so far in people who were injected with its Covid-19 vaccine Ad5-nCoV.

The announcement follows US federal health agencies' recommendation on Tuesday that the use of Johnson & Johnson's Covid-19 vaccine, which uses similar technology to CanSinoBIO's product, should be paused for at least a few days after six women younger than 50 developed rare blood clots after receiving the shot.

"No blood clot-related serious adverse events have been reported in around one million vaccinations of Ad5-nCoV," CanSinoBIO said in a filing.

CanSinoBIO's shares fell as much as 13.7 percent and 18.4 percent in Shanghai and Hong Kong, respectively, in morning trading.

Vaccines from Johnson & Johnson and CanSinoBIO contain another virus called adenoviruses, which have been modified to essentially render them harmless.

The adenoviruses are employed as a vector to ferry instructions for human cells to make parts of the new coronavirus, triggering the immune system to produce antibodies against it.

CanSinoBIO's Covid-19 vaccine, which has been approved in China and secured deal in Mexico, uses a different adenovirus than that for Johnson & Johnson's.

- Reuters