Merck & Co. said an experimental pneumonia vaccine it’s developing spurred an immune response that was equal to Pfizer’s market-leading Prevnar 13, reporting Wednesday summary details from two key Phase 3 trials.In one of the studies, Merck’s candidate outperformed Pfizer’s shot on three strains of pneumonia-causing bacteria that are major drivers of disease. Merck plans to ask the Food and Drug Administration for approval of its vaccine later this year, while Pfizer is due to soon report late-stage study data for its own next-generation pneumococcal shot.Vaccines already on the market can prevent disease caused by up to 23 different strains of pneumococcal bacteria. But strains not covered by current vaccines are becoming increasingly responsible for new pneumonia cases.

For years, Pfizer has led the pneumococcal vaccine market with Prevnar 13, which launched in 2010 and prevents invasive disease resulting from 13 strains of the bacteria. The shot is Pfizer’s biggest selling product, earning nearly $6 billion in sales in 2019.

Launched in 1983, Merck’s Pneumovax 23 addresses 23 bacterial strains, but Centers for Disease Control and Prevention guidelines had until late last year suggested it only be used in series after Prevnar 13 in people age 65 and older.

The change, which recommends “shared clinical decision-making” before receiving a Prevnar 13 shot, came in part because routine vaccination of children with Prevnar 13 had driven disease levels from its 13 strains in older people to “historically low levels.”

Pneumovax is a much smaller drug for Merck, bringing in $926 million in sales in 2019.

With the current clinical programs, each company is trying to compete with the other’s vaccine. Merck’s new drug, V114, inoculates against 15 bacterial strains, while Pfizer’s covers 20.

In the results announced Wednesday from the PNEU-AGE trial, V114 in healthy adults age 50 and older met “non-inferiority” in stimulating an immune response to the 13 strains addressed by Prevnar 13, and superiority for strains 22F and 33F, which Prevnar doesn’t cover. Those two strains cause 13% of invasive pneumonia cases in people 65 and older, Cantor Fitzgerald analyst Louise Chen wrote in a Sept. 9 note to clients.

A secondary test in PNEU-AGE measuring the immune response stimulated by V114 to strain 3 also found V114 superior to Prevnar 13. Merck described that strain as “a leading cause of invasive pneumococcal disease globally.”

Merck also reported results from another trial, dubbed PNEU-TRUE, which compared immune response stimulated by three different manufacturing lots of V114, and all were found to be similar.

Pfizer’s new vaccine, code-named PF-06482077, aims to cover 20 bacterial strains. The pharma has also reported Phase 3 data, announcing March 18 that it had stimulated an equivalent immune response to all 13 strains blocked by Prevnar 13 and six of the seven PF-06482017 has in common with Pneumovax 23. The seventh missed that benchmark “by a small margin.”

The competition could drive significant new sales for both companies, Cantor’s Chen wrote in a January note to clients, estimating potential annual sales of $7 to $10 billion cumulatively over the next decade.