An RNA vaccine candidate, BNT162b1, is shown to induce a robust immune response in healthy adults aged 18–55 years in an interim report of a phase 1/2 clinical trial published in Nature.
RNA vaccine platforms, which use messenger RNA to elicit an immune response, are generally considered safe and have facilitated the rapid development of vaccines against SARS-CoV-2. Delivered intramuscularly, BNT162b1, which encodes a SARS-CoV-2 receptor-binding domain antigen, is one of several RNA vaccine candidates that are being studied in parallel for selection to advance to a trial of their safety and efficacy.
Judith Absalon and colleagues report interim data from an ongoing phase 1/2 clinical study of BNT162b1. Forty-five healthy adults (23 men and 22 non-pregnant women; 37 participants were white) aged 18–55 years were randomized to receive 10 micrograms (μg), 30 μg or 100 μg of BNT162b1, or a placebo. Participants in the 10-μg and 30- μg 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, which increased with dose level, in the seven days following vaccination, including pain at the injection site, fatigue, headache, fever and sleep disturbance.
The vaccine elicited a robust immune response in participants, which increased with dose level and with a second dose. Antibodies against SARS-CoV-2 were present 21 days after a single vaccination at all dose levels, and there was a substantial increase in SARS-CoV-2-neutralizing antibodies 7 days after the second 10-μg or 30-μg dose was given. The immune response was much stronger in the 30-μg group than in the 10-μg group. However, there were no notable differences in immune response between the 30-μg and 100-μg groups after one dose, and as participants who received the 100-μg dose also experienced greater side effects, they did not receive a second dose.
Participants’ levels of neutralizing antibodies were 1.9 to 4.6 times higher than those in patients recovering from SARS-CoV-2 infection. However, although this comparison provides a benchmark for evaluating the vaccine-elicited immune response and the vaccine’s potential to provide protection, phase 3 trials are needed to determine the efficacy of BNT162b1. The study is also enrolling adults aged 65–85 years, and later phases will prioritize the enrolment of more-diverse populations.
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