mRNA Covid-19 vaccine remained safe and efficacious through 6 months

1. The mRNA Covid-19 vaccine, BNT162b2, has maintained its favorable safety profile through 6 months following vaccination.

2. Despite a gradual decline, BNT162b2 remained highly efficacious in preventing Covid-19, including severe disease and the new beta-variant.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Two years following its emergence, the Covid-19 pandemic continues to affect the world, having caused more than 187 million cases and 4 million deaths. The mRNA Covid-19 vaccine BNT162b2 was among the first approved to prevent its spread and more than 1 billion doses have been distributed to date. BNT162b2 was originally reported to be safe and 95% effective against Covid-19 at 2 months following immunization. The current study is a randomized controlled follow-up trial to assess the efficacy and safety of BNT162b2 at 6 months after immunization. The safety profile of BNT162b2 observed at 2 months was maintained: adverse events were more common than with placebo but few led to trial withdrawal. Despite an estimate BNT162b2 was also shown to continue being effective against symptomatic Covid-19 infection, severe Covid-19, as well as the beta-variant. Although the placebo-controlled period has ended as placebo recipients have now been immunized, the study established evidence of continued safety and efficacy of BNT162b2 against Covid-19, 6 months after the receipt of the second dose.

Click here to read the study in NEJM

Relevant Reading: Safety, Immunogenicity, and Efficacy of the BNT162b2 Covid-19 Vaccine in Adolescents

In-Depth [randomized controlled trial] This study is a 6-month follow-up placebo-controlled, observer-blinded trial to assess the efficacy and safety of BNT162b2, an mRNA Covid-19 vaccine. 44,165 participants: 16 years of age or older and 2,264 participants 12 to 15 years were randomly assigned to receive two 30-μg doses (3 weeks apart) of BNT162b2 or placebo. Participants who were healthy or had stable chronic conditions were included. Participants who had a compromised immune system or a history of Covid-19 were excluded. Safety endpoints included local reactions, systemic events, antipyretic or analgesic use, and serious adverse events. Efficacy was measured against laboratory-confirmed Covid-19 with an onset of 7 days or more after the second dose. Additionally, efficacy against severe Covid-19 and various lineages of SARS-CoV-2 were also reported. Adverse events were found to be more common in the BNT162b2 group than placebo: 30% vs. 14%, as well as related adverse events (24% vs. 6%) and severe adverse events (1.2% vs. 0.7%), with few leading to trial withdrawal. New adverse events that were not previously reported included decreased appetite, lethargy, and malaise. Death rates were comparable between the BNT162b2 and placebo groups and none were attributable to BNT162b2. Among 42,094 participants 12 years of age and older with no history of Covid-19, new infection was observed in 77 BNT162b2 recipients and 850 placebo recipients, which translates to a 91.3% efficacy rate (95% confidence interval [CI], 89.0 to 93.2). In 44,486 participants with or without evidence of previous Covid-19, 81 cases were observed in the BNT162b2 group and 873 cases in the placebo group, corresponding to a 91.1% efficacy rate (95% CI, 88.8 to 93.0). Conversely, the previous infection was estimated to confer 72.6% protection. Severe Covid-19 with an onset after the first dose occurred in 1 BNT162b2 recipients and 30 placebo recipients, corresponding to efficacy of 96.7% (95% CI, 80.3 to 99.9). Lastly, BNT162b2 was found to confer 100% protection (95% CI, 53.5 to 100) against the B.1.351 (beta) variant in the South African study cohort. Overall, the efficacy rate was estimated to decline by 6% every 2 months. A notable limitation is that the blinded placebo-controlled period was limited by the ethical need to immunize placebo recipients. Furthermore, the results did not address whether vaccination prevented asymptomatic infection. Nevertheless, the study provided concrete evidence of the safety and efficacy of the mRNA Covid-19 vaccine at 6 months post-immunization.

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