Pfizer and BioNTech's vaccine shows robust immune response

The RNA vaccine candidate developed by Pfizer and BioNTech has been shown to induce a robust immune response in a preliminary clinical trial conducted with 45 healthy adults aged 18-55 years, the results of which are published today in Nature.

BNT162b1 is the most promising of the four vaccines developed by the US pharmaceutical company Pfizer and the German company BioNTech, all of which are based on messenger RNA to elicit an immune response. These types of vaccine candidates are generally considered safe and have facilitated the rapid development of SARS-CoV-2 vaccines. 

Based on interim data from the Phase 1/2 clinical trial conducted to assess vaccine safety, tolerability, and immunogenicity, BNT162b1, which is administered intramuscularly, was tested in 45 healthy adults (23 men and 22 non-pregnant women; 37 participants were white) aged 18-55 years.

The candidates - randomly assigned - received 10 micrograms (μg), 30 μg or 100 μg of BNT162b1, or a placebo; in addition, participants in the 10μg and 30μg groups also received a second dose on day 21. 

The authors found that BNT162b1 was generally well tolerated, although some participants experienced mild to moderate side effects within seven days of vaccination, which increased with dose level.

The most common adverse reactions were local pain at the injection site, fatigue, headache, muscle pain, chills, fever, and sleep disturbances. However, the vaccine caused a robust immune response in participants, which increased with dose level and with a second dose.

Antibodies to SARS-CoV-2 remained 21 days after the first vaccination at all dose levels, and a substantial increase in neutralizing antibodies to SARS-CoV-2 was recorded seven days after the second dose of 10-μg or 30-μg was administered. The immune response was much stronger in the 30-μg group than in the 10-μg group. 

However, there was no noticeable difference in the immune response between the 30-μg and 100-μg groups after the first dose, and since participants who received the 100-μg dose also experienced increased side effects, they did not receive a second dose.

Participants' neutralizing antibody levels were 1.9 to 4.6 times higher than those of patients recovering from SARS-CoV-2 infection.

However, although this comparison provides a benchmark for assessing the immune response provoked by the vaccine and its potential to provide protection, phase 3 trials are needed to determine the efficacy of BNT162b1. 

Adults aged 65 to 85 are being recruited for this study, and priority will be given in subsequent phases to recruiting more diverse populations, the study notes.