A COVID-19 vaccine candidate co-developed by the pharmaceutical giant Pfizer and the German biotech company BioNTech induces a "robust" immune response in healthy adults aged 18-55 years, according to an interim report of an early phase clinical trial, published in the journal Nature on Wednesday.
The researchers noted that BNT162b1 is an RNA vaccine that elicits an immune response by mimicking the mRNA molecule used by the novel coronavirus SARS-CoV-2 to build its infectious proteins.
According to the study the vaccine candidate is delivered intramuscularly, and enables human cells to produce proteins part of the SARS-CoV-2 receptor-binding domain, against which the immune system is trained to produce antibodies.
They said such vaccines are generally considered safe and have facilitated the rapid development of vaccines against SARS-CoV-2.
They said it 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.
In the ongoing phase 1/2 trial, the scientists assessed the safety, side effects, and safe dose of the vaccine candidate in 45 healthy adults (23 men and 22 non-pregnant women) aged 18-55 years.
The participants were randomised to receive 10 micrograms (g), 30 g or 100 g of BNT162b1, or a placebo, the study noted.
Participants in the 10-g and 30-g groups also received a second dose on day 21, the scientists said.
Based on the study, the researchers said 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.
They said the vaccine elicited a "robust immune response" in participants, which increased with dose level, and with a second shot.
According to the study, 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-neutralising antibodies seven days after the second 10-g or 30-g dose was given.
It noted that the immune response was much stronger in the 30-g group than in the 10-g group.
However, the scientists said there were no notable differences in immune response between the 30-g and 100-g groups after one dose, and as participants who received the 100-g dose also experienced greater side effects, they did not receive a second dose.
They said the participants' levels of neutralising antibodies were 1.9 to 4.6 times higher than those in patients recovering from SARS-CoV-2 infection.
Although this comparison provides a benchmark for evaluating the vaccine-elicited immune response and the vaccine's potential to provide protection, the researchers believe phase 3 trials are needed to determine the efficacy of BNT162b1.
They said the study is also enrolling adults aged 65-85 years, adding that later phases would prioritise the enrolment of more-diverse populations.
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