The risk of heart attack and stroke is increased three-fold in the first two weeks following Covid-19, according to a study published in The Lancet journal.

The study compared the occurrence of acute myocardial infarction or heart attack, and stroke in 86,742 Covid-19 patients with 348,481 control individuals in Sweden from February 1 to September 14, 2020.

"We found a three-fold increased risk of acute myocardial infarction and stroke in the first two weeks following Covid-19," said Osvaldo Fonseca Rodriguez from Umea University in Sweden, and co-first author of the study.

The risk was the same even after the researchers adjusted for known risk factors for acute myocardial infarction and stroke such as comorbidities, age, gender and socio-economic factors.

"The results indicate that acute cardiovascular complications represent an important clinical manifestation of Covid-19," said Ioannis Katsoularis from Umea University, a co-author of the study.

"Our results also show how important it is to vaccinate against Covid-19, in particular the elderly who are at increased risk of acute cardiovascular events, Katsoularis said.

The researchers used two statistical methods in the study: the matched cohort study and the self-controlled case series.

The self-controlled case series study is a method that was originally invented to determine the risk of complications following vaccines, they said.

"Both the methods suggest that Covid-19 is a risk factor for acute myocardial infarction and ischaemic stroke," the authors of the study said.

"This indicates that acute myocardial infarction and ischaemic stroke represent a part of the clinical picture of Covid-19, and highlights the need for vaccination against Covid-19," they said.

In the study, information from national registries from the Public Health Agency of Sweden, Statistics Sweden and the National Board of Health and Welfare were cross-linked for all reported Covid-19 patients.

A control group consisting of four individuals matched to every Covid-19 case on age, gender and county of residence, that had not tested positive for Covid-19.

By using historical registry data from the National Board of Health and Welfare's inpatient registry, individuals with a previous myocardial infarction and stroke were identified and excluded from the study.

"It would have been difficult to calculate the risk that Covid-19 contributes to acute myocardial infarction and stroke, if individuals with a prior event were included," said Krister Lindmark, a co-author of the study.

"This is because the risk of a recurrent acute myocardial infarction and stroke is increased following a first acute myocardial infarction or stroke," Lindmark added.