German biotech CureVac (CVAC  ) released disappointing preliminary efficacy results for its COVID-19 vaccine candidate on Wednesday, dimming hopes that the vaccine can meet any regulatory approvals.

The vaccine candidate, CVnCoV, demonstrated an interim efficacy of 47% against SARS-CoV-2 at "any severity," and "did not meet prespecified statistical success criteria," CureVac stated in a press release. For comparison, annual flu vaccines are usually in the range of 40% to 60% effective. The study found varying levels of efficiency among different age groups and certain mutant strains of the virus may affect efficacy.

Compared to other mRNA vaccines, CVnCoV also falls short. Both shots developed by Pfizer (PFE  )-BioNTech (BNTX  ) and Moderna (MRNA  ) offer about 95% effectiveness against symptomatic COVID-19 infection. CVnCoV's advantages of remaining stable at refrigerator temperatures for months and offering a lower cost option with fewer mRNA molecules per dose seem to have brought its downfall of low efficacy.

CureVac plans to complete a final analysis of the results in the coming weeks.

Both the World Health Organization and the U.S. Food and Drug Administration require a COVID-19 vaccine to be at least 50% effective to be considered for emergency authorization.

"We we were hoping for a stronger interim outcome, we recognize that demonstrating high efficacy in this unprecedented broad diversity of variants is challenging. As we are continuing toward the final analysis with a minitm of 80 additional cases, the overall vaccine efficacy may change," said Dr. Franz-Werner Haas, chief executive officer, in a statement. "In addition, the variant-rich environment underlines the importance of developing next-generation vaccines as new virus variants continue to emerge."

CureVac's late-stage trial of approximately 40,000 participants, conducted in partnership with Bayer (BAYRY  ), found a high prevalence of variant strains across 10 countries in Latin America and Europe. In total, the study's researchers found that more than half of the 124 COVID-19 cases sequenced were caused by Variants of Concern. Most cases were caused by the emerging Lambda variant, which was first identified in Peru.

Beyond its own vaccine candidate, CureVac is working on second-generation COVID-19 vaccine candidates in partnership with GlaxoSmithKline (GSK  ). "These candidates are based on new mRNA backbones and include potential variants in multivalent vaccine formats as well as combination vaccines for potential protection against multiple infectious diseases in one vaccine," according to CureVac.

Both companies expect to begin clinical testing in the third quarter of this year.