A newly published peer-reviewed study has reported an increased risk of certain rare adverse events among teenagers following completion of a two-dose series of mRNA COVID-19 vaccines.
The study, published last week in Scientific Reports, analyzed health data from 496,432 adolescents aged 12 to 19 in Norway, using records from the Norwegian Patient Registry and the Norwegian Cause of Death Registry.
Conducted by 13 researchers affiliated with Norwegian health institutions, the study assessed short- and mid-term safety outcomes among vaccinated and unvaccinated teenagers.
According to the study, teenagers who received a two-dose series of the Pfizer-BioNTech or Moderna mRNA COVID-19 vaccines showed:
A fivefold increase in the rate of myocarditis and pericarditis following the second dose (adjusted incidence rate ratio of 5.27) compared to unvaccinated peers.
A 37-fold higher rate of myocarditis and pericarditis among 12- to 15-year-olds after the two-dose series, although researchers noted this finding was based on a small number of cases.
The study found that adverse event rates were generally higher after the second dose compared to the first. Heart-related conditions were primarily identified among 18- and 19-year-olds, a group previously identified in other research as being at elevated risk for myocarditis.
Importantly, the researchers reported no vaccine-related deaths and found no statistically significant association with all-cause mortality within 28 days of receiving two doses.
German Tapia, Ph.D., a researcher with the Norwegian Institute of Public Health and one of the study’s co-authors, told The Epoch Times that “the number of observed outcomes and statistically significant associations were generally low, with some exceptions.”
The study authors concluded that their findings “confirm the SARS-CoV-2 mRNA vaccine safety,” while acknowledging that many of the adverse events identified were rare and that estimates could be less reliable due to small case numbers.
Despite the study’s conclusion affirming overall vaccine safety, several independent commentators and vaccine-safety advocates offered a more critical interpretation of the data.
READ ALSO: Emails expose concerns within CDC, FDA over COVID-19 vaccine data mining system
Dr. Clayton J. Baker, an internal medicine physician, argued that the findings reinforce concerns about increased risks following second doses, particularly with regard to myocarditis and anaphylaxis. He described the reported tenfold increase in anaphylactic reactions as “very alarming.”
Steve Kirsch, founder of the Vaccine Safety Research Foundation, noted that several of the strongest associations appeared dose-dependent, occurring mainly after the second dose. He said this pattern “strongly suggests” a causal link.
Karl Jablonowski, Ph.D., senior research scientist at Children’s Health Defense (CHD), pointed out that a significant portion of adolescents in the sample did not receive a second dose. He suggested that this may have influenced outcome comparisons, particularly in younger age groups.
The researchers acknowledged key limitations in their study, including the rarity of some adverse events and the relatively short “risk windows” used to measure outcomes — ranging from two to 56 days post-vaccination, depending on the condition examined.
Some critics argued that these time frames may not fully capture delayed-onset events. For example, Baker suggested that conditions such as appendicitis or myocarditis could potentially manifest beyond the selected observation periods.
The authors did note that certain statistically significant associations were observed outside the predefined risk windows, including cases of appendicitis, anaphylactic reactions, myocarditis, and pericarditis when focusing on adolescents without prior reported COVID-19 infection.
A secondary age-stratified sensitivity analysis also identified statistically significant associations for certain outcomes, including acute appendicitis, facial nerve palsy, anaphylaxis, and all-cause death. However, the researchers maintained that these findings should be interpreted cautiously due to the small number of cases.
The debate over myocarditis risk following mRNA COVID-19 vaccination in adolescents has been ongoing since early in global vaccination campaigns. Multiple health authorities have acknowledged a small but elevated risk of myocarditis, particularly in young males after the second dose, while emphasizing that cases are generally rare and often mild.
The Norwegian researchers called for further adolescent-focused studies, particularly in relation to new mRNA vaccines and booster doses, to better understand age-specific safety outcomes.
The study adds to the broader scientific discussion surrounding the balance of risks and benefits of COVID-19 vaccination in younger populations, particularly as infection rates, variant severity, and public health strategies continue to evolve.
Public health agencies in many countries continue to monitor vaccine safety data and emphasize that decisions regarding vaccination policy are based on ongoing risk-benefit evaluations informed by emerging evidence.