Vaxcyte pneumococcal vaccine succeeds in Phase 3 trial

Vaxcyte announced on October 5, 2026, that its experimental pneumococcal vaccine, VAX-31, successfully met all primary endpoints in a Phase 3 trial of over 3,500 adults. The vaccine matched or exceeded the efficacy of Pfizer's Prevnar 20 and Merck's Capvaxive across 28 shared strains and showed superior protection on unique strains. Following the news, Vaxcyte's shares surged over 50%, pushing its market value past $12 billion as analysts hailed the data as a best-case scenario for challenging Pfizer's dominant market share.

Phase 3 trial efficacy results

• ▪In a Phase 3 trial of over 3,500 adults aged 50 and older, VAX-31 matched the effectiveness of Pfizer's Prevnar 20 and Merck's Capvaxive across 28 shared bacterial strains
• ▪VAX-31 missed a stricter statistical benchmark on two strains shared with Merck's Capvaxive, but met a historical threshold on those strains
• ▪VAX-31 demonstrated superior immune responses compared to rival vaccines against three bacterial strains unique to VAX-31 and against strain 20B
• ▪Vaxcyte announced on October 5, 2026, that its experimental pneumococcal vaccine, VAX-31, met all primary efficacy endpoints in its first Phase 3 clinical trial

Vaccine safety and tolerability

• ▪Vaxcyte reported that VAX-31 was well tolerated with a safety profile similar to Prevnar 20 and Capvaxive, showing no serious vaccine-related adverse events
• ▪The most common adverse events from VAX-31 were generally mild-to-moderate and the majority resolved within two days of vaccination

Financial analyst assessments

• ▪Mizuho Securities analyst Salim Syed characterized the Phase 3 trial results as a near best-case scenario showing best-in-class potential in an $8 billion annual market
• ▪Leerink Partners analyst David Risinger stated that VAX-31's minor statistical misses against Merck's Capvaxive are unlikely to affect its regulatory approval chances
• ▪Jefferies analyst Roger Song stated that the trial results hit the blue-sky case, positioning VAX-31 to capture significant share of the adult vaccine market

Investor sentiment and expectations

• ▪Vaxcyte shares surged between 50% and 57% in morning trading on October 5, 2026, following the Phase 3 trial announcement, pushing its total market valuation past $12 billion
• ▪In May 2026, some Wall Street investors became skeptical of VAX-31's prospects after Vaxcyte executives implied the vaccine might miss against some strains covered by Capvaxive

Future clinical and regulatory timeline

• ▪Vaxcyte plans to submit a U.S. marketing application for VAX-31 in the first half of 2028
• ▪Vaxcyte expects to report results from two additional late-stage clinical trials of VAX-31 in the first half of 2027

Vaccine design and testing

• ▪In earlier testing, VAX-31 matched the effectiveness of Pfizer's 20-strain pneumococcal vaccine
• ▪VAX-31 is designed to protect against 31 bacterial strains, whereas Pfizer's Prevnar 20 covers 20 strains and Merck's Capvaxive covers 21 strains

Pfizer's vaccine franchise

• ▪Pfizer's pneumococcal vaccine business was built on a 13-strain shot that emerged in 2010 and later expanded to a 20-strain alternative
• ▪Pfizer's dominant pneumococcal vaccine franchise generated more than $6 billion in revenue in 2025