New study shows risk of heart inflammation following COVID-19 infection and vaccination
Research published in Nature Medicine looks at the possible link between different heart conditions and COVID-19 infection or vaccination.
The QCOVID research team, led by Professor Julia Hippisley-Cox at the University of Oxford, with members of the Usher Institute involved including Professor Aziz Sheikh and Professor Nick Mills, has published a new study looking at the risk of heart inflammation and other heart conditions in COVID-19 infection and vaccination.
Summary in Plain English
The Oxford-AstraZeneca (ChAdOx1), Pfizer-BioNTech (BNT162b2) and Moderna (mRNA-1273) vaccines have all been tested in clinical trials, and found to be safe and effective against COVID-19 disease and death.
These vaccines were approved for use in the UK between December 2020 and April 2021.
As people were vaccinated in the tens of millions, small numbers of heart-related side effects were reported globally for the Pfizer-BioNTech and Moderna vaccines.
These vaccines are both ‘messenger ribonucleic acid’ (mRNA) vaccines. They use pieces of genetic information from the SARS-CoV-2 virus, to help the immune system identify and fight a future infection.
The most common heart-related side effects reported were:
- Myocarditis: inflammation/swelling of the heart
- Pericarditis: inflammation/swelling of the fluid-filled lining around the heart.
As of 9 July 2021, the European Medicines Agency (EMA) had reported:
- 145 myocarditis and 138 pericarditis cases after 177 million doses of Pfizer-BioNTech
- 9 myocarditis and 19 pericarditis cases after 20 million doses of Moderna
So far, no reports of myocarditis or pericarditis have been reported for the Oxford-AstraZeneca vaccine.
Why did we carry out this research?
Studying vaccine safety using data from a national population can identify rare side effects that might not show up in clinical trials.
We wanted to understand if there was a link between people having myocarditis or pericarditis and getting the first or second dose of a vaccine. We also wanted to know whether the risk after being vaccinated is higher or lower than the risk of the same condition in people who have tested positive for a SARS-CoV-2 infection.
What data did we use?
To do this, we used data on the vaccine type, date and doses for all vaccinated people in England, aged 16 or older. We included vaccine doses given between 1 December 2020 and 24 August 2021.
We linked these data to national death records, hospital admissions, information about people’s SARS-CoV-2 infections, and personal circumstances like age, sex, location and health.
We looked for links between side effects in the heart, and first and second doses of the three UK COVID-19 vaccines. We included having an irregular heartbeat (cardiac arrhythmia) as well as myocarditis and pericarditis in our analysis.
We used the same group of people to look at the risk of these conditions following a SARS-CoV-2 infection, both before and after vaccination. This self-comparison helps to account for variations in the health and life circumstances of each person.
What did we find?
38.6 million people over 16 in England had at least one dose of a vaccine in the study period. Of these, 32.1 million people had a second dose:
- 19.8 million people had two doses of the Oxford-AstraZeneca vaccine
- 12.0 million people had two doses of the Pfizer-BioNTech vaccine
- Over 360,000 people had two doses of the Moderna vaccine.
People having the Moderna vaccine as a first dose were younger on average, because the rollout of this vaccine started later.
Of the people who had at least one vaccine, 3.0 million had a positive PCR (‘polymerase chain reaction’) test for SARS-CoV-2. The majority of these infections were before vaccination (2.3 million).
We found 397 people who were admitted to hospital or died of myocarditis in the 28 days after either the first or second dose of a vaccine. Out of these, 359 people had also had COVID-19, either before or after vaccination.
In our analysis, there was a significantly increased risk of myocarditis for people in 1-28 days after a first and second dose of the Moderna vaccine.
We calculated the number of extra cases of myocarditis per 1 million people following a vaccine:
- 0-3 cases after first dose of Oxford-AstraZeneca
- 0-2 cases after first dose of Pfizer-BioNTech
- 2-8 cases after first dose of Moderna
- 7-11 cases after second dose of Moderna.
This is compared to 38-41 extra cases of myocarditis in 1-28 days after a positive test.
We found 356 people who were admitted to hospital or died of pericarditis in the 28 days after either the first or second dose of a vaccine. Out of these, 188 had also had COVID-19, either before or after vaccination.
In our analysis, we did not find any association between pericarditis and the Pfizer-BioNTech or Moderna vaccines. The Oxford-AstraZeneca vaccine reduced the risk of pericarditis, and having a SARS-CoV-2 infection significantly increased it.
Around 86,000 people were admitted to hospital or died from cardiac arrhythmia within 1-28 days of a vaccine. Of these, just under 40,000 had tested positive for SARS-CoV-2, either before or after vaccination.
Having a first or second dose of either the Oxford-AstraZeneca or Pfizer-BioNTech vaccine decreased a person’s risk of having an irregular heartbeat. There was an increased risk following the second dose of a Moderna vaccine.
The risk of a person having cardiac arrhythmia after COVID-19 was over five times higher than for someone who has not been infected.
Why is this study important?
To date, this is the largest study to look at side effects in the heart after COVID-19 disease or vaccination that also compares different vaccines.
It shows that there is no increased risk of pericarditis or cardiac arrhythmia in the 1-28 days after vaccination, except after the second dose of a Moderna vaccine. Both of these conditions are more likely after a SARS-CoV-2 infection.
There is an increased risk of myocarditis for people after the first dose of the three vaccines available in the UK, as well as after the second dose of a Moderna vaccine. However, this is still at least four times lower than the number of extra cases of the condition after a SARS-CoV-2 infection. The majority of vaccine-related myocarditis events have been mild, but may need to be monitored in the long term.