Late Wednesday, German pharmaceutical CureVac announced what it called “sobering” news about its experimental covid-19 vaccine candidate: In the interim results from a large clinical trial, the vaccine appeared to be only 47% effective. This latest disappointment is a reminder of how lucky the U.S. has been to have access to highly effective vaccines created in a relatively short time with few stumbles.
CureVac’s Phase III trial of its candidate, an mRNA vaccine in the vein of those already developed by Moderna and Pfizer/BioNTech, involved 40,000 participants in 10 countries across Latin America and Europe. CureVac’s candidate faced harsher headwinds than earlier vaccines, though, as it was tested during a time when several concerning variants of the coronavirus have widely spread, at least some of which appear to partly evade the immunity that would be provided by vaccines created against the original strain of the virus.
According to the company’s reporting of the data (which has yet to be seen by the scientific community at large), there were at least 13 distinct variants found among the 134 people who contracted covid-19 during the trial; more than half of these infections involved variants of concern. All told, the vaccine was found to be 47% effective at preventing any level of illness from covid-19—below the bare minimum of 50% effectiveness needed for approval in many countries, including the U.S.
“While we were hoping for a stronger interim outcome, we recognize that demonstrating high efficacy in this unprecedented broad diversity of variants is challenging,” said Franz-Werner Haas, CEO of CureVac, in a statement from the company.
Though there’s still a chance the results could look better by the time of the full analysis (meant to include 80 more confirmed cases of covid-19 across the control and treatment groups), it’s more likely that the vaccine will sputter out. If so, it would join four other vaccine candidates that were abandoned during development, including two others that had reached clinical trials.
There have also been challenges for covid-19 vaccines that managed to pass clinical trials and reach the public. China’s widely distributed Sinopharm and Sinovac vaccines seem to have been substantially less effective in the real world than the clinical trial data suggested, with countries that relied on them like Chile and Seychelles still having faced large outbreaks after successful vaccination campaigns. Other vaccines, like AstraZeneca’s and Johnson & Johnson’s, have experienced their own troubles, from safety concerns to disastrous production delays.
Through it all, though, Pfizer and Moderna’s vaccine rollouts have largely gone smoothly in the U.S., where the majority of Americans have been vaccinated with either one. They remain highly effective against all the variants so far identified, and no wide-reaching serious side effects have been identified (there may be a very rare risk of heart inflammation among younger people, but it’s still being studied).
It will take time to find out why CureVac’s mRNA vaccine isn’t as effective as its cousins, though some outside scientists have already speculated that small differences in the mRNA design used across these vaccines may be to blame. If that’s the case, it further emphasizes the luck we’ve had. One tiny structural tweak here, one production misstep there, and the U.S. may have had a much harder time combatting the pandemic these past few months. Other not-so-lucky countries have experienced renewed peaks during this same time period, fueled by the arrival of more potent variants and the shortage of effective vaccines (a shortage, it should be said, that countries like the U.S. have played a part in causing).
Until everyone worldwide has access to these vaccines, the pandemic will continue to jump from peak to peak, killing and sickening more people. CureVac’s pending failure may not matter for the U.S., but it’s yet another stumble that the rest of the world can hardly afford.