Sanofi and GlaxoSmithKline say their COVID-19 vaccine triggers a strong immune response, bolstering the late-comer program's potential as a booster shot

• Sanofi and GlaxoSmithKline said that their experimental COVID-19 vaccine succeeded in a mid-stage trial.
• The pharma giants plan to launch a pivotal-stage study with 35,000 volunteers in the coming weeks.
• The shot suffered from disappointing data and delays in 2020. The companies now hope for approval by year's end.

One of the world's most closely watched coronavirus vaccine programs reported positive data on Monday from a mid-stage clinical trial, paving the way for the start of a massive human trial that could allow the shot to be authorized before the end of this year.

Sanofi and GlaxoSmithKline, two of the largest vaccine-makers in the world, said in a press release that their experimental coronavirus vaccine led to strong immune responses across all ages in a study that enrolled 722 volunteers. It's a much-needed piece of positive news for the two industry leaders, which saw their vaccine effort delayed by disappointing data announced in December, and have fallen far behind rivals like Moderna, Pfizer-BioNTech, and Johnson & Johnson.

Read more: GlaxoSmithKline stumbled with COVID-19 shots. Now it's facing an exodus of US talent and an uncertain future as the world's vaccine leader.

The companies did not release specific data on the antibody response, nor did they publish results in a peer-reviewed medical journal or post a paper on a preprint server.

Instead, the companies issued a press release describing the neutralizing antibody responses as "comparable to those generated by natural infection."

Neutralizing antibodies are the virus-fighting proteins that play a critical role in our immune response. GSK and Sanofi added that younger volunteers had generally stronger immune responses to the vaccine.

The two pharma giants expect to launch a final-stage clinical study, called a Phase 3 trial, in the coming weeks that will enroll more than 35,000 people. They also plan to simultaneously run smaller studies that test their vaccine, including versions tailored to neutralize specific coronavirus variants, as booster shots in people who've already been immunized.

If everything goes to plan, Sanofi and GSK expect their vaccine to be approved in October, November, or December of 2021, the companies said.