Two of the world's leading vaccine manufacturers have run into a big problem with their joint coronavirus vaccine program. Lackluster immune responses from some of the first patients injected with a candidate developed by Sanofi (SNY -0.78%) and GlaxoSmithKline (GSK -0.44%) led the partners to announce on Friday morning that they were delaying the phase 3 trial that they'd planned to start this month.
Interim results from the companies' phase 1/2 clinical trial showed the original vaccine formulation generated sufficient immune responses in volunteers aged 18 to 49. Unfortunately, the immune responses it produced in older adults were lower than levels seen among patients who have successfully recovered from COVID-19.
The partners aren't abandoning their recombinant protein-based coronavirus vaccine candidate, but the tests of it at its current concentration won't go much further. Instead, Sanofi and GlaxoSmithKline plan to begin a phase 2 clinical trial testing an improved formulation of their COVID-19 vaccine candidate in February.
That study will include a group randomized to receive an authorized vaccine for comparison. This will most likely be a messenger-RNA (mRNA) based vaccine candidate from Moderna (MRNA 2.96%), or Pfizer (PFE -1.03%), and BioNTech (BNTX 2.63%). BNT162b2 from Pfizer and BioNTech is likely to receive emergency use authorization from the FDA on Friday afternoon following the positive outcome of Thursday's independent advisory committee meeting. Moderna's candidate, mRNA-1273 will be the subject of a similar meeting on Dec. 17.
The key component of the vaccine candidate developed by Sanofi is a protein that resembles a portion of the SARS-CoV-2 virus responsible for COVID-19. It's delivered in combination with an adjuvant made by GlaxoSmithKline to enhance the immune system's response to the antigens. This old-fashioned method of training the immune system has worked for generations, but it's beginning to look like the mRNA-based approach has a strong efficacy advantage. We'll know more when a head-to-head trial reads out next year.