Vaxcyte Shares Jump About 30% as VAX-31 Clears All Primary Endpoints in Pivotal OPUS-1 Trial

Vaxcyte shares surged roughly 30% after the company reported that its 31-valent pneumococcal conjugate vaccine candidate, VAX-31, met all primary endpoints in OPUS-1, a pivotal Phase 3 trial in adults. StockTitan reported the stock move as +29.52% versus the previous close on heavy trading volume, while CNBC described the midday jump as "about 30%" following the release of top-line results from the trial in adults aged 50 and over.

The data, detailed in a company statement carried by StockTitan, cover immunogenicity, immunobridging and safety comparisons against two already-marketed pneumococcal vaccines, Pfizer's Prevnar 20 (PCV20) and Merck's Capvaxive (PCV21).

OPUS-1 Results: Clearing the Bar on Immune Response

According to the StockTitan report, VAX-31 met the noninferiority criterion, a lower bound confidence interval (LBCI) above 0.667, on all 32 serotype opsonophagocytic activity (OPA) geometric mean ratio comparisons tested in the trial's immunobridging analysis, which compared adults aged 18-49 with adults aged 50-64. That set of 32 comparisons includes the 31 vaccine serotypes plus a cross-reactive serotype, 20B.

On the superiority side, the three serotypes unique to VAX-31, together with cross-reactive serotype 20B, met a stricter prespecified superiority criterion (LBCI above 2.0) against PCV20 and/or PCV21, clearing all four of those comparisons, per the statement.

In separate head-to-head comparisons against each individual comparator, VAX-31 met the LBCI above 0.667 noninferiority threshold for all 20 serotypes it shares with PCV20 and for 17 of the 19 serotypes it shares with PCV21.

Two Serotypes Miss the Stricter Standard Against PCV21

The two shortfalls both came in comparisons with PCV21: serotypes 3 and 12F missed the LBCI above 0.667 criterion but met a historical LBCI above 0.5 threshold, which Vaxcyte's statement describes as a prespecified key secondary endpoint. Company Chief Scientific and Operating Officer James Wassil said, in the statement carried by StockTitan, that "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," adding that PCV20 remains an important comparator for serotypes 4 and 19F, which are not contained in PCV21.

Safety Profile Described as Comparable to Existing Vaccines

On the trial's primary safety endpoint, Vaxcyte's statement said VAX-31 was well tolerated with a safety profile similar to PCV20 and PCV21 across all ages studied. No serious adverse events were considered related to the study vaccines, and there were no discontinuations due to adverse events, according to the release. Solicited local and systemic reactions tracked from Day 1 through Day 7 were generally mild to moderate, with most resolving within 48 hours and no meaningful differences observed across cohorts, the statement said. Immune responses were measured one month after vaccination, while safety follow-up continues for six months. In the adult High Dose formulation used in the trial, all serotypes are dosed at 3.3 mcg except serotypes 1, 5 and 22F, which are dosed at 4.4 mcg.

Positioning Against Prevnar 20 and Capvaxive

CNBC characterized the readout by noting that VAX-31's immune responses were comparable to those of Prevnar 20 and Capvaxive, the two active comparators used in the trial. Vaxcyte's own materials describe VAX-31 as the broadest-spectrum pneumococcal conjugate vaccine candidate currently in clinical development, built using XpressCF, a cell-free protein synthesis platform the company licenses exclusively from Sutro Biopharma.

The company's statement also includes a design estimate: VAX-31 is intended to cover approximately 95% of invasive pneumococcal disease (IPD) and approximately 88% of pneumococcal pneumonia circulating among U.S. adults aged 50 and older. By our calculation using those two company-provided figures, the IPD coverage estimate is 7 percentage points higher than the pneumonia coverage estimate (95 minus 88), a relative difference of roughly 8% (7 divided by 88, times 100). This is a company design estimate rather than a trial-measured efficacy outcome, and it should be read as such.

Vaxcyte Chief Medical Officer Luis Jodar framed the strategic pitch in the statement by pointing to tradeoffs in the current market: "Today's adult PCVs differ in the serotypes they cover, requiring tradeoffs between coverage of currently circulating disease-causing serotypes and preserving coverage of historically important serotypes." He said VAX-31 is designed to bring both considerations into a single 31-valent vaccine. CEO Grant Pickering, in the same statement, said the results were produced "in a trial inaugurating a more stringent noninferiority standard" that he said "sets a new benchmark for the class" and gives the company confidence in the vaccine's approval potential.

Regulatory Timeline and What Comes Next

Vaxcyte said it expects results from two additional adult Phase 3 trials, OPUS-2 and OPUS-3, in the first half of 2027. Those results are intended to support a planned Biologics License Application submission to the FDA in the first half of 2028, subject to regulatory review, followed by a manufacturing consistency study, according to the company statement.

On the infant side of the program, Vaxcyte said it plans to report topline safety, tolerability and immunogenicity data from a VAX-31 infant Phase 2 dose-finding study, covering both the three-dose primary immunization series and a booster dose, either sequentially or together, by the end of the first half of 2027. In May 2025, the FDA expanded VAX-31's Breakthrough Therapy designation to include prevention of pneumococcal pneumonia in addition to invasive pneumococcal disease in adults, a decision the company statement said was based on positive topline results from an earlier adult Phase 1/2 study.

Bottom Line

The OPUS-1 top-line data, as described in Vaxcyte's statement, met both prespecified primary endpoints: noninferiority on all 32 serotype OPA GMR comparisons in the immunobridging analysis of adults aged 18-49 versus adults aged 50-64, and a safety profile similar to PCV20 and PCV21 at all ages studied. The shortfalls came in the prespecified individual comparator analyses, where two serotypes — 3 and 12F — missed the stricter LBCI above 0.667 threshold against PCV21, though both cleared the historical LBCI above 0.5 threshold the company says was a prespecified key secondary endpoint. The roughly 30% share move reported by CNBC and StockTitan reflects how much weight investors placed on a clean primary-endpoint readout for a candidate whose BLA submission is not planned until the first half of 2028. Our reading of the company's own framing is that the decisive regulatory question is how the FDA weighs the PCV21 comparison given current U.S. epidemiology — with the next scheduled data points, OPUS-2 and OPUS-3, not expected until the first half of 2027.