Vaxcyte says its 31-strain pneumococcal shot met Phase 3 goals against Prevnar and Capvaxive

The strongest part of this study is that it tested one new vaccine against both market leaders in a single randomized trial. Participants were assigned at random to VAX-31, Prevnar or Capvaxive ^[6], so the three groups should be alike in age and health. The same investigators then measured all of them ^[7]. When results come from separate trials, a difference in population or lab method can look like a difference between vaccines. Randomizing within one study removes most of that risk.

Counting serotypes sets a minimum for new coverage. VAX-31 must include at least 11 serotypes that Prevnar lacks and at least 10 that Capvaxive lacks ^[9][10]. The initial report did not list which serotypes the three shots share, give strain-by-strain antibody figures, or define the primary endpoints.

Those figures matter because the result for a 31-serotype shot ^[2] has two halves. One is whether its responses keep pace with Prevnar and Capvaxive on the serotypes they have in common. The other is how strong its responses are on the serotypes each rival lacks. Vaxcyte said the vaccine hit its primary endpoints ^[1]. Until the numbers are published, that statement is the company's own summary of both halves.

Antibody strength is one step removed from illness. The trial compared immune responses ^[7]. The direct test of protection would be a count of pneumococcal disease among vaccinated people.

In my view the result makes Vaxcyte a credible entrant for adults 50 and older ^[6], with one condition. Its responses on the shared serotypes have to hold up against Prevnar and Capvaxive in the full data. A broader shot that loses ground on the serotypes the incumbents already cover would be harder to sell than its count suggests. STAT calls the market at stake lucrative ^[8].