Regret it or not, the Zika vaccine Sanofi walked away from shows early promise

Preliminary results from a trio of phase 1 studies showed promise for the Zika vaccine Sanofi had previously left behind.

The purified, inactivated Zika vaccine (ZPIV) candidate Sanofi left behind amid mounting political pressure over pricing has shown promise in a trio of phase 1 studies, having elicited robust neutralizing antibody responses in almost all vaccine recipients.

Researchers injected 67 early participants from three sites in the U.S. with either two injections of the Zika vaccine or placebo. Among 52 vaccine recipients, 48 (92%) had seroconverted, reaching a geometric mean titer threshold of 1:10, which means that they’ve developed meaningful antibodies. Only mild to moderate adverse events were observed.

Published in The Lancet, these results are of course still preliminary and therefore cannot guarantee the vaccine’s efficacy. But they offer an early glimpse into the vaccine’s safety profile and immunogenicity.

RELATED: Takeda pushes U.S.-backed Zika vaccine into the clinic

“Our results are limited by short-term follow-up, but data from longer-term follow-up will be published to indicate the durability of vaccine-elicited immune responses and expanded safety information,” the study authors wrote.

Across the three phase 1 trials, researchers are enrolling more subjects and testing the shot in stronger doses or with a third vaccination.

Plus, a fourth trial is underway in Puerto Rico to test the vaccine in a community with high prevalence of natural flavivirus immunity. Such trials are important because they will address concerns about antibody-dependent enhancement, an effect in people with flavivirus exposure prior to vaccination that could limit a vaccine’s application.

The vaccine was developed by the Walter Reed Army Institute of Research, which is also conducting one of the early-phase studies at its Silver Spring, Maryland, site. Sanofi had planned to license it from the U.S. Army but was practically forced out of the deal in September.

RELATED: Sanofi pulls out of Zika vaccine collaboration as feds gut its R&D contract

Sanofi’s decision was never about the vaccine’s promise. Public figures including Sen. Bernie Sanders, I-Vt., had pressed for pricing guarantees, and then the waning Zika epidemic made it more difficult to conduct trials. As a result, the Biomedical Advanced Research and Development Authority’s pulled funding for much of the project. Sanofi had to bow out in response.

BARDA, however, is still supporting a similar ZPIV candidate from Takeda, which just started human testing. In an email response to Reuters, Col. Nelson Michael of WRAIR said the U.S. Army was looking to license their ZPIV to other companies.