Pre-clinical trials were conducted in non-human primates (rhesus macaques) and mice. Vaccinated primates, who were challenged with SARS-CoV-2 virus, had no virus detected in the lower respiratory tract and clearance of virus in the nose within three days. These results indicated the vaccine may reduce both infection and transmission.

The US Phase 1 trial included participants aged 18 – 85 years old and compared a placebo to one of two vaccine candidates (BNT162b1, which encoded the SARS-CoV-2 receptor-binding domain; or BNT162b2, which encodes the SARS-CoV-2 full-length spike protein). This trial supported the selection of BNT162b2 (full length spike protein) for advancement to Phase 2/3 trials.

Two doses of BNT162b2 were shown to elicit high SARS-CoV-2 neutralising antibody titres and robust spike protein-specific T-cell responses.

Safety profile

During clinical trials, symptoms following immunisation with Comirnaty were generally mild to moderate and generally short-term. They were less common and milder in older adults (>55 years), compared to younger adults (<55 years). Local reactions including pain (66-83%) and redness (5-7%) at the injection site were more common after the first dose compared to the second dose. Systemic reactions (including fatigue, headache, muscle ache and headache) were more common and severe following the second dose. The incidence of serious adverse events was low and similar in both the vaccine and placebo groups.

Vaccine efficacy

Phase 3 trial data showed 95% vaccine efficacy. Similar vaccine efficacy (generally 90 to 100%) was observed across all subgroups defined by age (>16 years), sex, race, ethnicity, baseline body-mass index, and the presence of co-existing conditions. Older adults, 65 years and over, also had the same vaccine efficacy as younger adults. An immune response was detected less than two weeks after the first dose, and a second dose three weeks later, boosted that response. The study was not designed to assess the efficacy of a single-dose regimen, however, in the interval between the first and second doses, the observed vaccine efficacy against COVID-19 was 52%, reaching full efficacy at least seven days after the second dose.

Paediatric clinical trials

2,260 adolescents (aged 12 to 15 years) were enrolled in a phase 3 trial in the United States (US). A good safety profile and strong immune response was observed with 100% efficacy 7 days after dose 2 of Comirnaty. 18 cases of COVID-19 infection observed in the placebo group (n=1,129) versus zero cases in the vaccinated group (n=1,131).

2,268 children (aged 5 to 11 years) participated in a phase 2-3 clinical trial. Participants in the vaccine group were administered a 2 dose course of 10 micrograms of Paediatric Comirnaty, 21 days apart. A similar safety profile to that seen in the ≥ 12 year old age group was observed in this younger cohort. A robust immune response was reported with a vaccine efficacy of 90.7% more than 7 days after the second dose. 3 cases of COVID-19 disease were observed in the vaccine group (n=5,157) and 16 cases among the placebo group (n=751).

Post-licensure surveillance


A true vaccine allergy (anaphylaxis) is a rare side effect occurring for all vaccines at a rate of approximately 1 case per million vaccine doses administered. Post-licensure surveillance of Comirnaty in the US has shown that it has a slightly higher rate of anaphylaxis with approximately 4.7 cases per million doses administered. Most cases (89%) occurred within 30 minutes of vaccination and 24% had a history of prior anaphylaxis.


A small number of cases of myocarditis and pericarditis have been reported in individuals vaccinated with COVID-19 mRNA vaccines (eg. Comirnaty and Moderna). Reports have predominantly involved adolescents and young adults, more commonly males, after the second dose of vaccine. Symptom onset has typically been seen within 4 days of vaccination.


Authors: MVEC Education Team

Reviewed by: Rachael McGuire, (MVEC Education Nurse Coordinator) and Francesca Machingaifa (MVEC Education Nurse Coordinator)

Date: September 15, 2022

Materials in this section are updated as new information and vaccines become available. The Melbourne Vaccine Education Centre (MVEC) staff regularly reviews materials for accuracy.

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