(Bloomberg) -- Moderna Inc. shares sank after new data showed the efficacy of its RSV shot fell sharply in the second year and was lower than that of rival vaccines.

The results could further raise doubts over the prospects for its shot, which is already third to the market. Moderna shares fell as much as 11%, their biggest intraday decline since November.

Moderna’s shot dropped from 55% efficacy over the first 12 months to 36% in the second year in patients with at least three “lower respiratory” symptoms of RSV, according to documents posted Wednesday on the Centers for Disease Control and Prevention website.

The efficacy of Pfizer Inc.’s shot declined from 86% in the first year to 74% in the second year. GSK Plc’s vaccine fell from 79% to 59%, according to a CDC presentation.

Jefferies analyst Michael Yee said in a research note that Moderna’s new figures were “on the lower end of expectations,” while pointing out that comparisons were difficult because the companies studied their vaccines during different seasons.

Moderna also presented updated data about its shot, called mRESVIA, during a CDC committee meeting that develops recommendations on how to use vaccines.

Last month, Moderna gained US approval for its RSV vaccine in older adults, giving the company a second product as it seeks to shake its reliance on the fading market for Covid-19 shots.

--With assistance from Robert Langreth.

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