Pfizer, BioNTech share clinical data linking favored COVID-19 vaccine to improved tolerability

Pfizer and BioNTech have published clinical data on the COVID-19 vaccine they advanced into phase 3. The early clinical data link the phase 3 candidate to a far lower rate of adverse events than another prospect, explaining Pfizer and BioNTech’s decision to move it into late-stage testing.

At the start of July, Pfizer and BioNTech shared phase 1/2 data on the b1 variant of their BNT162 mRNA vaccine. The update, coupled with a subsequent release of data from the same trial, linked the vaccine to increases in neutralizing antibodies, CD4 and CD8 T cells, and immune-modulatory cytokines, putting Pfizer and BioNTech in a position to move into phase 3.

The partners duly started a 30,000-subject phase 3 trial late last month, but one key detail was a big surprise. Rather than move the b1 vaccine into phase 3, Pfizer and BioNTech selected its sibling, b2. At that stage, Pfizer and BioNTech were yet to share clinical data on b2. 

Now, the partners have presented data that back up their belief that b2 was the right candidate to take forward. The safety and tolerability profile is the big difference between the b1 and b2 vaccines. 

In a preprint paper, Pfizer and BioNTech revealed that 17% of 18- to 55-year-olds who received 30 μg of the b2 vaccine reported related adverse events. That compares to 50% of people who received b1. A big difference was also seen in the cohort of 65- to 85-year-olds. Nobody in that cohort who took 30 μg of b2 reported a vaccine-related adverse event, compared to 17% in the b1 study.

Pfizer and BioNTech also found systemic events experienced by people who received b2 were milder than those affecting their counterparts who took b2. Fever affected 17% of 18- to 55-year-olds who received b2, compared to 75% of people in the b1 group. In general, severe systemic events such as fatigue, headache, chills, muscle pain and joint pain happened less often in the b2 patients.

With b1 and b2 eliciting similar immune responses, the adverse event data helped persuade Pfizer and BioNTech to take the latter vaccine into phase 3. More tolerable vaccines may be more likely to be accepted by large numbers of people, boosting efforts to quickly vaccinate populations. 

Pfizer and BioNTech think they may be in a position to seek approval for b2 in October, putting them at the front of the race to bring a vaccine to market. The trial has now enrolled more than 11,000 people and begun administering second doses to some participants.