Vaccine maker Novavax Inc said on Tuesday its COVID-19 shot retooled against the omicron BA.1 variant showed a strong immune response as the fourth dose and met the main goal of strain change in a late-stage study.

Data showed the shot, NVX-CoV2515, produced 1.6 times the amount of neutralizing antibodies in people who had previously not been exposed to COVID-19 compared to Novavax's original coronavirus vaccine.

The trial included Novavax's so-called bivalent vaccine, the BA.1-tailored shot and its prototype vaccine.

Novavax says the results from the study showed its omicron-tailored shot can be changed to target a new variant vaccine if necessary.

It added the bivalent vaccine — aimed at combating the BA.1 version of omicron and the original virus strain first detected in China — did not show any benefit over its BA.1-tailored shot or its prototype vaccine.

Meanwhile, the prototype vaccine produced a broad immune response against the original strain of the virus as well as both BA.1 and BA.5 omicron variants, data showed, but the company did not disclose details about the levels of antibodies produced in the study.

The U.S. Food and Drug Administration in June recommended COVID vaccine makers change the design of their booster shots to include components tailored to combat the omicron BA.4 and BA.5 subvariants.

Novavax's COVID shot has not yet received approval in the United States as a second booster dose. The FDA allowed the use of its shot as first booster in adults in mid October, and since then shares of the Maryland-based company have risen nearly 13%.

Novavax, like rivals Moderna Inc and Pfizer Inc , is also developing a combination vaccine targeting both COVID-19 and influenza.