Covid Vaccines: An Update on Balancing Risks and Benefits

A new large, multi-country study has confirmed what previous smaller studies found: Covid-19 vaccines have risks. In particular, the messenger RNA (mRNA) vaccines from Pfizer and Moderna were associated with increased risk of heart problems for males under 40, and the viral vector vaccine from Astra Zeneca was associated with a significant increase in neurological and hematologic problems. This information ought to be used to update U.S. vaccination recommendations, particularly for young people who have little risk of severe Covid-19 disease or death.

Covid vaccines reduce the disease’s severity and risk of death and provide partial, short term — measured in a few months — protection against infection. But those benefits are less important for groups with a low baseline risk, and they must be balanced against the risks associated with vaccination. 

The new study, conducted by the CDC-funded Global Covid Vaccine Safety Project, evaluated the risk of adverse events from the three original Covid-19 vaccines with the highest numbers of doses administered in 99 million vaccinated individuals across eight developed countries — Argentina, Australia, Canada, Denmark, Finland, France, New Zealand, and Scotland — between December 2020 and August 2023. It calculated observed versus expected ratios for 13 different conditions that previous studies had indicated might be increased following Covid-19 vaccinations. 

The study found multiple statistically significant associations among the vaccines and various adverse events. The researchers then applied strict statistical criteria — beyond the usual standard of statistical significance — to select which of the associations had the highest likelihood of being true, what the authors termed a “prioritised safety signal.”

The two mRNA vaccines met the prioritized-safety-signal criteria for increased risk of myocarditis (inflammation of the heart muscle) following first, second, or third doses. Both vaccines were statistically associated with an increased risk of pericarditis (inflammation of the sac surrounding the heart), although only the Moderna vaccine met the prioritized-safety-signal criteria.

The Astra Zeneca vaccine was associated with various neurological conditions. But only Guillain-Barré syndrome — where a person’s immune system attacks their nerves, resulting in tingling, muscle weakness, and sometimes paralysis that usually (but not always) resolves over several weeks — met the prioritized-safety-signal criteria. A prioritized safety signal was also found for the Astra Zeneca vaccine and the hematologic condition called cerebral venous sinus thrombosis — formation of a blood clot in the brain’s venous sinuses that prevents blood from draining out of the brain and sometimes leads to a hemorrhage into the brain. 

The association of Astra Zeneca’s viral vector vaccine and neurological and hematologic conditions is of limited significance to the U.S. because Astra Zeneca’s vaccine was not used in this country. The Johnson & Johnson Covid-19 vaccine was a viral-vector vaccine approved and used here. However, it only accounted for about 3 percent of the vaccines approved in 2020–21 and administered in the U.S. against the original viral variant; it has been discontinued. The mRNA vaccines from Pfizer (59 percent) and Moderna (38 percent) accounted for nearly all the vaccines administered against the original variant.

Read the full article at National Review.