Data on the Pfizer vaccine (Comirnaty)
A research group in the United States investigated the safety and efficacy of the Pfizer vaccine in 2,260 adolescents (referred to as children in this study) aged 12–15 years.9
Half the group (1,131 children) received the two doses of the vaccine 21 days apart, while the other half (1,029 children) received two doses of placebo – a dummy injection of saline (salt water). Injections of the vaccine or the placebo were given into muscle, usually the arm. Neither the vaccine providers nor the children knew which they were going to receive.9,10 This is called a double-blind placebo-controlled trial.
Over half of the study participants were followed up for at least two months after the second dose to see if there were any long-lasting or serious side effects.9,10
The efficacy of the Pfizer vaccine was assessed in children from 12–15 years of age, the majority of whom who had no evidence of previous infection with COVID-19.
Among the children with no evidence of previous infection, none of those in the vaccine group developed COVID-19 compared to 16 children in the placebo group who developed COVID-19 at least 7 days after the second dose. These study results showed that the vaccine was 100% effective at preventing COVID-19 (although the true rate could be between 75% and 100%) based on scientific analysis.4,9,10
The study also showed that the immune response to the Pfizer vaccine in children aged 12–15 was comparable to the immune response in older age groups (16–25 years). Immune response is measured by the level of antibodies that the body produces against the coronavirus that causes COVID-19 (SARS-CoV-2).
The health experts evaluating the results of the study concluded that the benefits of the Pfizer vaccine in this age group outweigh the risks, especially in children who have conditions that increase the risk of severe COVID-19 disease.4,9,10
Read more about clinical trials and why they are important
What did they learn about side effects from the Pfizer vaccine?
The most commonly reported side effects in the 12–15-year age group were the same as those reported by adults in earlier phases of the study: pain at the injection site, tiredness, headache, chills, muscle/body aches, fever and joint pain. The side effects were usually mild to moderate and went away within a few days following vaccination.4,9,10
Similar to the occurrence of side effects seen in adults who received the Pfizer vaccine, it appears that vaccine side effects in children are more likely to occur after the second dose.
Since the commencement of the Australian national vaccination program in February 2021, safety evaluation data has been gathered from over 1 million people who received the first dose of Pfizer and over 770,000 people who received both doses. The two most commonly reported side effects were:
- injection site pain (30% following the first dose vs. 43% after the second dose)
- tiredness (21% after the first dose vs. 43% after the second dose).
Symptoms were generally mild and short-lived.11
This information is useful for people giving and receiving the vaccination to know to expect some mild side effects after either dose, but even more so after the second dose. The safety evaluation of the Pfizer COVID-19 vaccine in 12–15 year-olds is ongoing.4,10
Rare side effects can happen with any medicine or vaccine. Health experts have acknowledged the difficulty detecting rare side effects from the vaccine due to the limited number of children included in the Pfizer study.12
It should be noted that in adults under 30 years of age, very rare cases of myocarditis and pericarditis (inflammation of the tissues surrounding the heart) have been observed following vaccination with Pfizer. These cases have mostly occurred within 14 days after vaccination, more often after the second vaccination, and more often in younger men.13 No cases of myocarditis or pericarditis have been observed in children 12–15 years who received the Pfizer vaccine as part of the US study.9
Data on the Moderna vaccine (Spikevax)
There is evidence that the Moderna vaccine has efficacy against symptomatic COVID-19 in people aged 12–17 years. This data comes from ongoing clinical trials involving around 4,000 participants aged 12–17 years of age.14
Study participants were randomly assigned to receive either two doses of the Moderna vaccine (2489 participants) or placebo (1243 participants). The two doses were given 28 days apart.
Efficacy against symptoms of COVID-19 was 92.7% two weeks following the first dose of the Moderna vaccine and 93.3% following the second dose, when compared with participants who were given the placebo injections. Results were similar to those reported in people aged 18–25 years who had received the Moderna vaccine.1,14
Were there side effects from the Moderna vaccine?
Side effects were reported after both doses but were more common after the second dose. Side effects included injection site pain, headache, fatigue, muscle aches and chills. Side effects that persisted for up to 28 days after any dose were more frequent in the vaccine group (20.5%) than the placebo group (15.9%). These included swelling at the injection site (4.3%) and headache (2.4%). No cases of myocarditis or pericarditis were reported.14
As yet, no Australian safety evaluation data has been gathered on the Moderna vaccine.
Find out more at AusVax Safety
Sometimes medicines, including vaccines, have unexpected and undesirable side effects. Any side effects should be reported. The Adverse Medicine Events Line provides a way of reporting and discussing adverse experiences with medicines.
Find out more about reporting side effects on the Adverse Medicines Events Line