In clinical trials of the experimental messenger RNA (ribonucleic acid) COVID-19 vaccine (BNT162b1), which is being developed by Pfizer, Inc. of New York and BioNTech SE of Mainz, Germany, adverse reactions have occurred in more than 50 percent of the adult participants. The Phase 1/2 human trials of BNT162b1 vaccine, which were conducted May-June 2020, involved 45 healthy adults between the ages of 18 and 55 years.1
In the trials, 12 of the adults were injected with a 10-microgram dose of the BNT162b1 vaccine, and 12 adults received a 30-µg dose, 12 a 100-µg dose, while nine adults were given a placebo of a sterile saline solution (0.9 percent sodium chloride injection, in a 0.5-mL dose). Within seven days after vaccination, seven (58.3 percent) of the participants in the 10-µg group reported adverse reactions (pain) near the injection site and 24–or 100 percent–in the 30-µg and 100-µg groups and two (22.2 percent) in the placebo group reported reactions. Severe pain was reported by one participant who received 100-µg dose.1 2
Three weeks after the initial vaccination with the BNT162b1 vaccine, each one of the clinical trial participants was given a second dose of the vaccine at the same dosage. Of the participants in the 10-µg group, 8.3 percent developed fevers. Of those in the 30-µg group, 75 percent developed fevers. More than 50 percent of the adults, who were given either a 10-µg or 30-µg dose, experienced an adverse reaction such as fever and sleep disturbances.1 2
Two participants suffered severe reactions. A Grade 3 fever of over 101.3°F two days after vaccination was experienced by one adult in the 30-µg group and sleep disturbance one day after vaccination was experienced by one adult in the 100-µg group.1 2
Grade 3 reactions are described by the U.S. Department of Health and Human Services (HHS) as, “severe or medically significant but not immediately life-threatening; hospitalization or prolongation of hospitalization indicated; disabling; limiting self care” such as “bathing, dressing and undressing, feeding self, using the toilet, taking medications.”3
According to the published results of the trials for the BNT162b1 COVID-19 vaccine being developed by Pfizer and BioNTech:
The most common systemic events reported in the 7 days after each vaccination in both BNT162b1 and placebo recipients were mild to moderate fatigue and headache. Reports of fatigue and headache were more common in the BNT162b1 groups compared to placebo. Additionally, chills, muscle pain, and joint pain were reported among BNT162b1 recipients and not in placebo recipients. Systemic events increased with dose level and were reported in a greater number of subjects after the second dose (10 µg and 30 µg groups).2
The clinical trial found that the experimental BNT162b1 vaccine was successful in generating antibodies against the SARS-CoV-2 virus. A recent STAT article noted, that some of the antibodies had a neutralizing effect in that they “appear to prevent the virus from functioning.” But it also pointed out that it is unclear if these antibody neutralizing levels will produce immunity to SARS-CoV-2.1 2
Pfizer and BioNTech plan to conduct larger clinical studies on their BNT162b1 vaccine later this summer.1
1 Herper M. Covid-19 vaccine from Pfizer and BioNTech shows positive results. STAT July 1, 2020.
2 Mulligan MJ, et al. Phase 1/2 Study to Describe the Safety and Immunogenicity of a COVID-19 RNA Vaccine Candidate (BNT162b1) in Adults 18 to 55 Years of Age: Interim Report. medRxXiv July 1, 2020.
3 U.S. Department of Health and Human Services. Common Terminology Criteria for Adverse Events (CTCAE). Nov. 27, 2017.