Large New Zealand Study Confirms Safety Profile of Pfizer-BioNTech Vaccine

A nationwide study in New Zealand confirmed the safety of the Pfizer-BioNTech COVID-19 vaccine while noting an association with rare cases of myo/pericarditis, particularly among younger patients, and acute kidney injury.

The study, posted on Preprints with The Lancet, included more than 4 million indivduals age 5 and older who received the Pfizer-BioNTech COVID-19 vaccine, BNT162b2, between Feb. 19, 2021 and Feb. 10, 2022, along with a historical comparison cohort.

Investigators reviewed health records to evaluate 12 adverse events of special interest (AESI) within 21 days of vaccination—acute kidney injury (AKI), acute liver injury, Guillain-Barré syndrome (GBS), erythema multiforme, herpes zoster, single organ cutaneous vasculitis, myo/pericarditis, arterial thrombosis, cerebral venous thrombosis (CVT), splanchnic thrombosis, venous thromboembolism (VTE) and thrombocytopenia.

“Although rare, a statistically significant association between BNT162b2 vaccination and myo/pericarditis and AKI was observed,” wrote the study authors, led by Muireann Walton, MSc, of the Ministry of Health New Zealand and Te Whatu Ora Health New Zealand. “While the association between BNT162b2 and myo/pericarditis has been confirmed internationally, further research is required to understand the association of AKI.

Following the first dose of the vaccine, the incident rate ratio of myo/pericarditis was 2.6 (2.2– 2.9) with a risk difference of 1.6 (1.1– 2.1) per 100,000 persons vaccinated. After the second dose, the IRR myo/pericarditis was 4.1 (3.7– 4.5) with a risk difference of 3.2 (2.6– 3.9) per 100,000 persons vaccinated.

The risk of myo/pericarditis was greatst among those ages 5 to 19 after the second dose of the vaccine, with an IRR of 25.8 (95% CI 15.6– 37.9).

“Importantly, the risk of myo/pericarditis is still low in individuals under 19 years old, with an excess of 2 and 5 events per 100,000 persons after the first and second dose of the vaccine respectively,” the study authors wrote.

They noted that awareness of the risk of myo/pericarditits in association with the vaccine may lead to over-identification.

“Most importantly, studies have found that the risk of myocarditis following SARS-CoV-2 infection is substantially greater than after COVID-19 mRNA vaccination,” the authors wrote. “It is generally considered that the benefits of vaccination with the BNT162b2 vaccine against COVID-19 continue to outweigh the risks from the disease.”

Incidence of acute kidney injury also increased, with an IRR of 1.6 (1.5– 1.6) after the first dose of the vaccine and 1.7 (1.6– 1.7) after the second dose. The increased risk of AKI was seen in all but the youngest group of study participants.

Most of the patients diagnosed with AKI were older than 65, had underlying diseases such as hypertension, diabetes and chronic kidney disease, which may have contributed to the kidney injury.

“While the association between BNT162b2 and myo/pericarditis has been confirmed internationally, further research is required to understand the association of AKI,” the authors wrote. “BNT162b2 was not found to be associated with most of the AESIs investigated, providing reassurances around the safety of the vaccine.”

The study authors noted that the limited sample size of clinical trials makes it impossible to detect all potentially serious adverse events.

In February 2022, the Centers for Disease Control and Prevention updated its COVID-19 vaccine guidelines to say some people may wait up to eight weeks before getting the second dose of the vaccine to decrease the slight risk of myocarditis.

Safety of the updated bivalent COVID-19 vaccine from Pfizer-BioNTech is currently under review over concern for ischemic stroke in people ages 65 and older.