The company now hopes to file for authorisation in the US and Europe in the third quarter of 2021, it said in a statement, sending shares tumbling 12%.

Novavax’s vaccine is key to the Covax programme, which was set up to try to ensure poor countries have equitable access to vaccines to combat the coronavirus pandemic.

Its NVX-CoV2373 vaccine candidate demonstrated 100% protection against severe disease in a Phase 3 clinical trial in Britain, with 89.7% efficacy against any form of the disease.

It uses a piece of the SARS-CoV-2 virus called the spike protein, which the company mass-produces inside insect cells, and can be stored at regular refrigeration temperatures.

Novavax also said Monday it had had positive results from preclinical studies of a shot combining its influenza and Covid vaccine candidates.

The company said a study, which will now undergo peer review, showed that the shot produced strong levels of antibodies against both diseases in ferrets and hamsters.

“Despite low rates during the Covid-19 pandemic, influenza remains a significant risk to global public health and the need for versatile, more effective vaccines is as important as ever, including against the flu,” said Gregory Glenn, the company’s president of R&D.

The new vaccine combines NanoFlu and NVX-CoV2373.

Hamsters that were vaccinated and then deliberately infected with the coronavirus retained their body weight compared to those that received a placebo.

Lung samples taken from the immunised animals after they were put down showed they were Covid-free.