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Serious health risks were not more common in the first 3 weeks after vaccination against Pfizer / BioNTech or Modern COVID-19 compared with 22-42 days later, reveals a first study of this type with more than 6 millions of people.
MRNA vaccination was not associated with increased risks for Guillain-Barré syndrome, myocarditis / pericarditis, stroke or other 20 serious outcomes, the results suggest.
“This is a fairly reassuring study for anyone who has received an mRNA vaccine or is thinking of getting one. We were working with a lot of data and we did a rigorous and very controlled analysis.” , said the author, chief physician, Dr. Nicola Klein. , he said Medscape Medical News.
Research is important because “the world is confident in safe and effective vaccines to end the COVID-19 pandemic,” said Klein, director of the Kaiser Permanent Vaccine Studies Center, a senior researcher in the Kaiser Permanent Research Division, and principal investigator of Vaccine Safety Datalink COVID-19 rapid cycle analysis.
Although no serious safety findings emerged in the phase 3 mRNA vaccine trials, ongoing surveillance of any safety issues “is critical to ensuring safety, maintaining confidence and informing policy,” they note. Klein and colleagues in the study, which was published online on September 3, 2021. within JAMA.
“Post-marketing safety monitoring is essential to detect rare or serious adverse events associated with the vaccine, especially due to the large number of individuals exposed,” agreed three doctors who wrote an editorial accompanying it.
Weekly security monitoring
These interim findings come from the evaluation of the Datalink Safety Vaccine (VSD) surveillance system of the Centers for Disease Control and Prevention (CDC) and reviews of medical records. The VSD includes data from more than 10 million people eligible for a COVID-19 vaccine from eight major health plans in the United States.
This study is based on weekly reports from December 14, 2020 to June 26, 2021.
Klein and colleagues compared severe health outcomes in the 3 weeks following the first or second dose of an mRNA vaccine with what could be expected regardless of vaccination, based on the events of a later period and in a secondary analysis of unvaccinated people.
The rates of anaphylaxis, acute respiratory distress syndrome, multisystem inflammatory syndrome, and narcolepsy were exceptions and were based on all cases observed at 84 days post-vaccination.
The research included 11,845,128 doses of mRNA vaccine administered to 6.2 million people. Of these, 57% were Pfizer / BioNTech doses and 43% were Moderna vaccines.
Main conclusions
No results associated with mRNA vaccination reached the preset threshold for a safety signal in the study. This is not to say that no adverse events will occur. During the 21-day study period, events ranged from 0 cases of Kawasaki disease to 1059 reports of ischemic stroke, for example.
In addition, the researchers reported 183 possible cases of anaphylaxis during days 0 to 1 after vaccination. Of these, 171 were completely reviewed and 55 were confirmed. 95% of confirmed anaphylactic events occurred in women, 98% on the day of vaccination and 83% after the first dose. Most people with confirmed anaphylaxis (78%) had a history of allergies. In addition, most anaphylactic reactions (87%) began within 30 minutes of vaccination.
“While the biological mechanism for increased incidence among vaccinated women is unclear, it may be related to genes, hormones, and environmental and immunological factors,” Klein and colleagues point out.
In addition, although no significant link emerged between mRNA vaccination and myocarditis or pericarditis, rates were higher among adolescents and younger adults.
The editorial authors also took note. “MRNA vaccination was associated with an excessive risk of myocarditis / pericarditis among those aged 12 to 39 with an estimated 6.3 [95% confidence interval, 4.9 to 6.8] additional cases per million doses on days 0 to 7 after vaccination “.
The editorial authors are Kimberly G. Blumenthal, MD, MSc, and Neelam A. Phadke, MD, MPH, both affiliated with the Rheumatology, Allergy, and Immunology Division at Massachusetts General Hospital in Boston, and David W Bates, MD, MSc. , with the General Internal Medicine Division at Brigham and Women’s Hospital in Boston.
The strengths of the study include the assessment of a large number of individuals and the use of population-based, geographically diverse, and weekly updated VSDs. Klein and colleagues also note several limitations, including the 21-day limit and the inclusion of only events that led to medical care, which could have caused an underestimation of the risk.
Steps to the future
VSD data collection and research based on it are ongoing. “We will continue to monitor the safety of all vaccines that protect against COVID-19,” Klein said.
The editorial authors note that “additional VSD follow-up will continue to assess whether there are clinically relevant adverse events associated with mRNA vaccination, including booster doses.”
JAMA. Published online September 3, 2021. Full text, Editorial
Klein received grants from the CDC during the study. Blumenthal, Phadke and Bates had no relevant financial relationships to reveal.
Damian McNamara is a Miami-based journalist. It covers a wide range of medical specialties, including infectious diseases, gastroenterology, and critical care. Follow Damian on Twitter: @MedReporter.
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