Skip to content
Home » Adverse events surveillance after 11.8 million COVID mRNA vaccine doses

Adverse events surveillance after 11.8 million COVID mRNA vaccine doses

A paper was just published that reviewed adverse events after 11.8 million COVID-19 mRNA vaccine doses were administered in the USA. Because it is the topic of discussion these days, I felt it was important to review this paper.

Even though anti-vaxxers love to claim excess adverse events after people receive the COVID-19 mRNA vaccine, there are excellent methods that the CDC has developed to monitor these issues in vaccines, and this new paper looks at one of them.

The news is good, in case you’re wondering.

COVID-19 mRNA vaccine adverse events

In a paper published in JAMA on 3 September 2021 by Nicola P Klein, MD Ph.D. and others reviewed data in the Vaccine Safety Datalink (VSD), which provides the CDC with medical data on vaccination histories, health outcomes, and subject characteristics. It is one of the best databases for reviewing adverse events post-vaccination and to help determine if there is a causal relationship because it has access to actual medical records.

The VSD is far superior to the Vaccine Adverse Events Reporting System (VAERS), which cannot show correlation or causation.

These researchers examined 23 serious adverse events in 6.2 million persons who received 11.8 million doses of either the Pfizer or Moderna COVID mRNA vaccine.

COVID-19 mRNA vaccine adverse events

In a rigorous statistical analysis, Klein et al. found no safety signals for any of the serious adverse events in the chart above. One caveat is that the numbers are, in some instances so low that the confidence intervals are quite large in some cases. For example, venous thromboembolism shows excess cases that are approximately 7.5 per million doses. However, the confidence interval ranges from -0.1 to 14.0. As more cases and doses are accumulated in future analyses, the confidence interval may become smaller and may indicate if there are actually additional cases.

Because of the ongoing concerns with myocarditis and pericarditis after COVID-19 vaccinations, the researchers looked closer at those results:

Although the researchers did not find any overall excess cases per million doses for myocarditis and pericarditis, they did notice excess cases in individuals aged 12-39 years old. The researchers wrote:

Cases were significantly clustered within the 0 to 5 days after vaccination (P < .001). In supplemental analyses using vaccinated concurrent comparators, incidence per 1 000 000 person-years during the risk vs comparison intervals and adjusted RR were 321 vs 35 (RR, 9.83; 95% CI, 3.35-35.77) during days 0 to 7 after vaccination, corresponding to 6.3 additional cases per million doses (95% CI, 4.9-6.8).

Although myocarditis and pericarditis usually resolve within a few weeks to months, it is a serious condition. However, this data shows that the number of excess cases is exceedingly small out of a million doses – around 2.0 to 11.2 after two doses.

In addition, the authors include an analysis using an unvaccinated comparator group in Supplementary eTable 6. Surprisingly, the table reports a significantly reduced risk of thrombosis with thrombocytopenia syndrome (p=0.004), hemorrhagic stroke (p<0.001), pulmonary embolism (p<0.001), and acute myocardial infarction (p<0.001) in the vaccinated 1-21 days post-injection compared to the unvaccinated comparator group. So there’s that.

never be afraid on typewriter
Photo by Suzy Hazelwood on


The authors concluded:

In this interim analysis of surveillance monitoring of more than 11.8 million doses of 2 mRNA vaccines in a diverse population and weekly analyses from December 14, 2020, to June 26, 2021, no vaccine-outcome association met the prespecified threshold for a signal. Incidence of selected serious outcomes was not significantly higher 1 to 21 days postvaccination compared with 22 to 42 days postvaccination for any of the outcomes. For the less frequent outcomes, CIs were wide and did not necessarily exclude clinically relevant increases associated with vaccination, and surveillance is ongoing.

This is one of the most thorough analyses of adverse events after receipt of either the Pfizer or Moderna COVID-19 mRNA vaccine. The statistical analysis shows that there are no excess adverse events post-vaccination, except for myocarditis and pericarditis in one age group, and even then the numbers are tiny, far below the risks of COVID-19 itself.

One last point. This analysis looked at up to 42 days post-vaccination for outcomes. I know there is a myth that adverse events appear years later – it just doesn’t happen. Vaccine temporal effects are extremely short-term, usually within hours or days. This study shows that as there were no differences in excess adverse events (statistically, none) between 1 to 21 days compared to 22 to 42 days.

This was a huge study, with over 11 million doses of the COVID-19 mRNA vaccines – there appears nothing that would signal a safety concern to any scientist.


  • Klein NP, Lewis N, Goddard K, Fireman B, Zerbo O, Hanson KE, Donahue JG, Kharbanda EO, Naleway A, Nelson JC, Xu S, Yih WK, Glanz JM, Williams JTB, Hambidge SJ, Lewin BJ, Shimabukuro TT, DeStefano F, Weintraub ES. Surveillance for Adverse Events After COVID-19 mRNA Vaccination. JAMA. 2021 Sep 3. doi: 10.1001/jama.2021.15072. Epub ahead of print. PMID: 34477808.
Michael Simpson
Liked it? Take a second to support Michael Simpson on Patreon!
Become a patron at Patreon!

Discover more from Skeptical Raptor

Subscribe to get the latest posts sent to your email.

Discover more from Skeptical Raptor

Subscribe now to keep reading and get access to the full archive.

Continue reading