Vaxcyte surges as its 31-strain pneumococcal vaccine meets main goals in pivotal trial

Vaxcyte's bet that a single shot can protect against more strains of pneumonia-causing bacteria than the market leaders has cleared its biggest test so far. The San Carlos, California, company said Monday that its 31-strain vaccine, VAX-31, met all of its main goals in a pivotal late-stage trial in adults, and its shares jumped about 59% in premarket trading.

By 8:30 a.m. ET, Vaxcyte (Nasdaq: PCVX) was at $89.90, up $33.42 from Friday's close of $56.48, which had valued the company at about $8.4 billion. Through Friday the stock was up 22% this year. Shares of Pfizer and Merck, whose vaccines were the comparators in the study, were little changed, each down less than half a percent.

These are topline results released by the company. They are not an approval, and the full data set has not yet been published.

What the trial showed

The study, called OPUS-1, enrolled 4,047 people at about 30 U.S. sites. Its main group, 3,572 adults aged 50 and older who had never received a pneumococcal vaccine, was randomly assigned in equal numbers to a single dose of VAX-31, Pfizer's Prevnar 20 or Merck's Capvaxive. Immune responses were measured a month later.

Like other recent pneumococcal vaccine trials, this one measured antibodies rather than infections prevented. For each strain, or serotype, VAX-31 had to show it was not meaningfully weaker than the approved vaccines, using a cutoff stricter than the one historically used in such studies.

All 28 serotypes that VAX-31 shares with one or both rivals met that goal. For the three serotypes found only in VAX-31, plus a related strain known as 20B, the bar was higher: the new vaccine had to produce clearly stronger responses, and it did. A separate group of 475 adults aged 18 to 49 produced responses comparable to those of 50- to 64-year-olds on all 32 serotype comparisons.

Vaxcyte said the vaccine was well tolerated, with a safety profile similar to the two approved shots. No serious adverse events were judged to be related to the study vaccines, and no participant left the trial because of side effects. Safety follow-up runs for six months after vaccination.

The Capvaxive caveat

The soft spot is in the one-on-one comparisons. Against Prevnar 20, VAX-31 met the stricter bar on all 20 shared serotypes. Against Capvaxive, it met it on 17 of 19. Serotypes 3 and 12F missed that bar but cleared the lower threshold historically used in vaccine studies, the company said.

That gap matters more than its size suggests. Merck designed Capvaxive specifically for adults, and when the Food and Drug Administration approved it in June 2024, the company said its serotypes accounted for about 84% of invasive pneumococcal disease in U.S. adults 50 and older, against about 52% for Prevnar 20, based on 2018-2021 government data.

Vaxcyte acknowledged the point. "Given current U.S. epidemiology, with the serotypes unique to PCV21 accounting for a larger share of adult disease, we expect the comparison of VAX-31 to PCV21 to be a particular focus of FDA review," said James Wassil, the company's chief scientific officer and chief operating officer. PCV21 is the company's shorthand for Capvaxive.

Why investors care

Pneumococcal vaccines are a large, established business. In an investor presentation filed Monday, Vaxcyte put combined 2025 pneumococcal vaccine sales reported by Merck, Pfizer and GSK at $8.5 billion and cited an industry estimate that the market could reach about $12 billion by 2030, driven mainly by adult use. It also noted that U.S. guidance in 2024 extended a universal recommendation to adults 50 and older, from 65 and older.

Vaxcyte's pitch is breadth without weaker protection. It says its manufacturing approach can add strains "while maintaining the magnitude of immune responses." Luis Jodar, the chief medical officer, said today's adult vaccines require "tradeoffs between coverage of currently circulating disease-causing serotypes and preserving coverage of historically important serotypes."

The company estimates that VAX-31 could cover the strains behind about 95% of invasive pneumococcal disease in U.S. adults 50 and older, or 13% to 36% more than current adult vaccines. Those figures describe which strains cause disease, not how well the vaccine prevents illness. Chief Executive Grant Pickering said the mix of broader coverage and robust immune responses "sets a new benchmark for the class," a claim regulators have yet to test.

What comes next

Any approval is still years away. Vaxcyte expects topline results in the first half of 2027 from two more Phase 3 studies: OPUS-2, which tests VAX-31 given alongside a seasonal flu shot in 1,390 people, and OPUS-3, in 752 adults previously vaccinated against pneumococcal disease. A manufacturing consistency study is to follow, and the company plans to submit a biologics license application in the first half of 2028.

The FDA had already given VAX-31 Breakthrough Therapy designation for preventing invasive disease in adults and expanded it in May 2025 to cover pneumonia. Results from a Phase 2 study of the vaccine in infants are due by the end of the first half of 2027.