Pfizer said that subjects in its Phase III study of BNT162b2, a candidate mRNA-based vaccine against SARS-CoV-2, have so far exhibited only mild-to-moderate side effects, with fatigue and headache being the two most common. The company, which is developing the vaccine as part of a collaboration with BioNTech, noted that over 12,000 participants have now received a second dose of BNT162b2.
"So far there has been no safety signal reported," remarked Mikael Dolsten, Pfizer's chief scientific officer. The drugmaker noted that more than 29,000 people have been recruited into the study, which has a target enrolment of 44,000.
In July, Pfizer and BioNTech said that BNT162b2 was chosen to advance into late-stage testing ahead of another candidate vaccine, dubbed BNT162b1, as it has better "tolerability parameters." Results from a Phase I study released last month showed that while both vaccines induced similar immune responses in younger as well as older adults, BNT162b2 was found to be "associated with less systemic reactogenicity, particularly in older adults."
Pfizer also reaffirmed that based on current infection rates it expects to get conclusive data on the efficacy of BNT162b2 by the end of October. Company executives explained that the board monitoring the trial will conduct its first review of the data for efficacy when a total of 32 coronavirus cases have been seen among participants. "What we are doing in terms of releasing data is very unusual," commented CEO Albert Bourla, adding "it is a must to release this data."
The safety of vaccines against COVID-19 has come into focus recently, after AstraZeneca was forced to halt its late-stage programme for AZD1222 following a serious adverse event suspected to be transverse myelitis. The study has been cleared to resume in the UK and other locations, including Brazil and South Africa, although it remains on hold in the US while the FDA investigates the matter.
For related analysis, see ViewPoints: AstraZeneca proves COVID-19 vaccines aren't too big to fail.
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