After a woman suffered a rare side effect, New Zealand has reported its first mortality linked to the Pfizer vaccination.

The COVID-19 Vaccine Independent Safety Monitoring Board (CV-ISMB), according to the country's health ministry, determined that the woman's death was caused by inflammation of the heart muscle, which was "possibly attributable to vaccination."

The matter has been sent to the coroner, and the formal cause of death is still to be ascertained.

Other medical problems were present at the time of her immunization, according to the CV-ISMB, which may have affected her death.

"This is the first example in New Zealand where a fatality has been connected to the Pfizer COVID-19 vaccine in the days following immunization," the ministry said in a statement, without specifying the woman's age.

The fatality, according to the government, was caused by myocarditis, a rare but well-known adverse effect of immunization.