Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine

Original: NEJM December 10, 2020

Author(s): Polack FP, Thomas SJ,Kitchin N et al.

Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine - article image

Reviewer: Stylianos Loukides, e-Learning Director

Published: 13 Dec, 2020

On December 10, 2020, Fernando Polack et al published a study in NEJM where they evaluated the safety and efficacy of the BNT162b2 vaccine. BNT162b2 is a mRNA-based vaccine that encodes the SARS-CoV-2 virus protein spike and uses a lipid nanoparticle as a vector.Exposure of the SARS-CoV-2 protein to the recipient’s immune system leads to an immune response to the specific protein and thus the body can rapidly respond to natural SARS-CoV-2 infection. This is a 2/3 phase study in which volunteers were randomly assigned to a 1: 1 ratio of either the active BNT162b2 vaccine or the placebo vaccine. Each volunteer received 2 doses with an interval of 21 days between them. The vaccine or placebo vaccine consisted of 0.3 ml solution for injection and was administered intramuscularly to the deltoid muscle of the upper extremity.

The study included volunteers aged 16 years and older who were healthy or had chronic stable health problems including but not limited HIV infection, hepatitis B or C. The study did not include immunocompromised patients and those receiving immunosuppressive therapy. In total, 43,448 volunteers received the vaccine, 21,270 received the BNT162b2 and 21,728 received the placebo. The primary outcome was the efficacy of BNT162b2 against confirmed Covid-19 with onset at least 7 days after the second dose in participants who had been without serologic or virologic evidence of SARS-CoV-2 infection up to 7 days after the second dose. Safety issues were also considered as primary outcome.

Among the volunteers who received BNT162b2, 8 cases of COVID-19 were recorded 7 days after the 2nd dose of the vaccine. Correspondingly, 162 cases of COVID-19 were reported among volunteers who received the placebo vaccine. The BNT162b2 vaccine was 95% effective in preventing COVID-19 (95% confidence interval 90.3-97.6). It is also important that the high efficiency rates (90% -100%) were maintained in the sub-analyzes in terms of age (16-55, over 55, 65 and over, 75 and over), gender (men, women), race (white, black, Hispanic-Latin, non-Spanish non-Latin, other race), nationality (Argentinean, Brazilian, American), body mass index (below 30, 30 and above) and the presence of comorbidities. In addition, it is worth noting that a total of 10 cases of COVID-19 were observed after the first dose of the vaccine. 9 were volunteers who had received a placebo vaccine and only 1 was a volunteer who had received BNT162b2.

In addition, this publication does not mention the rates of asymptomatic COVID-19 infections and the possible protection offered by the vaccine. These data are expected in a future publication. The efficacy and safety of the vaccine in children, pregnant women, and immunocompromised patients who were not included in the study also remains a question. Regarding vaccine safety, data were based on a follow-up period of at least 2 months from the 2nd dose of the vaccine and the most common side effects were short-term and included pain and erythema at the injection site, bowel movement and headache. Other systemic symptoms such as fever and lymphadenopathy were less common. The rate of severe adverse events was low and did not differ between the BNT162b2 group and the placebo group. Based on the follow-up period and the number of volunteers, there are no concerns about the safety of the vaccine. Of course, the monitoring of the participants will continue in order to identify any distant side effects.

Following the publication of the results of the study in the New England Journal of Medicine, an independent panel of experts and advisers from the US Food and Drug Administration (FDA) issued a statement a few hours ago recommending vaccination with BNT162b2 and opening the pathway for approval for emergency use by the US Supreme Drug Regulatory Authority (FDA).

Finally, it should be noted that the forthcoming approval of the vaccine is the primary step, which should be followed by a great deal of effort to ensure the required vaccination coverage of the population to achieve collective immunity.


  • The need for two-dose vaccination, the need for transport and storage at -70 ° C, and the attitude of the public towards the vaccine are key challenges that need to be addressed.
  • In conclusion, the BNT162b2 vaccine effectively paves the way for tackling the COVID-19 pandemic and returning to everyday life.
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