The authors of the research paper looked at associations between 12 adverse conditions and the Pfizer vaccine between February 2021 and February 2022. They compared the historic rate of these conditions in New Zealand with rates after vaccination.
It found no link between vaccination and the majority of the selected adverse events, including nerve and blood-related conditions.
However, the Covid-19 vaccination was associated with a “rare but significant increased risk of myo/pericarditis”, the paper said.
The study estimated an excess of two cases of myo/pericarditis per 100,000 people vaccinated after the first dose of the vaccine and an excess of three cases of per 100,000 people vaccinated following the second dose of the vaccine.
Myocarditis is the inflammation of the heart muscle and pericarditis is the swelling of the tissue around the heart. Both conditions can be caused by viral infections like Covid-19, and are also rare side effects of the Covid-19 vaccine.
The risk of heart conditions after vaccination was higher in the under-19 age group, at five extra cases per 100,000 people after the second dose.
The study’s authors acknowledged that this finding was most likely the result of the different comparison groups used in the study. Background data used to calculate an “expected” rate of adverse events for young people was based on 0-to-19 year-olds, while data on the “observed” rate was based on people aged between 5 and 19.
“These findings provide further reassurance on the safety profile of the vaccine, particularly from a New Zealand-specific context,” said Dr Tim Hanlon, from Te Whatu Ora’s National Immunisation Programme.
“Importantly, studies have found that the risk of any of these [adverse events] following infection with SARS-CoV-2 (Covid-19) is substantially greater than after Covid-19 mRNA vaccination.”
Dr Hanlon said the study had been submitted for peer view with an unnamed journal.
Association Professor Helen Petousis-Harris, a vaccinologist at the University of Auckland, said the research paper picked up a known safety issue with the vaccine - myocarditis had been found as a rare side effect in international studies.
She warned against reading too much into the research, noting that the background rates of adverse effects in the study and post-vaccination rates came from different sources.
“There are limitations to these kinds of studies,” she said. “I would be cautious in over-interpreting any of this as we do have a lot of data internationally and it has not found these outcomes.”
“It’s also clear that the safety profile of this vaccine is very well understood through the culmination of vast amounts of international data.”
Professor Peter McIntyre, an epidemiologist at the University of Otago, said the vaccine’s link with myocarditis was picked up and communicated very early in New Zealand. While some had complained at the apparent speed at which the vaccine was introduced, he said this had likely saved many lives.
“One thing to emphasise is that the checking and double-checking of the vaccine was really well done in New Zealand. And the [risk] information was added - maybe not as quickly as we might have ideally liked - but it was still quickly and it was still something that was acknowledged and carefully followed.”
He said that while the study provided further reassurance about the vaccine programme at the height of the pandemic, it was now time to reassess the blanket approach of targeting all age groups for Covid vaccination.
“The older population is going to have to keep having yearly boosters, possibly even more, because they’re continuing to be at risk.
“But for young people, having had their two doses, and in most cases having had an infection, the picture is different ... and the risk of myocarditis is still there, even though it’s rare. So we may need to start moving away from everything for everyone to … specific targeted messaging for groups.”
MEDSAFE FINDINGS
As of November, four possible deaths have been linked to the Covid-19 vaccine in New Zealand.
Medsafe said 184 deaths were reported to the Centre for Adverse Reactions Monitoring (Carm) following the Covid vaccine.
Of that total, 163 were found to be unlikely to be related to the Covid-19 vaccine, 15 could not be assessed because of insufficient information, and two cases were still under investigation.
Two deaths have been determined by the coroner to be the result of myocarditis following a first dose of the Pfizer vaccine, and one was likely due to vaccine-induced myocarditis, but was awaiting a ruling from the coroner. In the fourth case, a link to the vaccine could not be excluded and myocarditis was found at the time of death, and a coroner was still investigating.
The rate of deaths following vaccination was lower than the expected number of natural deaths, Medsafe reported.
Up to August, there had been 500 spontaneous reports of myocarditis, pericarditis or myopericarditis within 30 days of vaccination.
“These reports do not necessarily have a causal relationship with administration of [the vaccine] and may represent coincidental events,” Medsafe said.
