Six Cases of Capillary Leak Syndrome After Moderna COVID Vaccination Being Investigated

The European Medicines Agency's (EMA) Pharmacovigilance Risk Assessment Committee (PRAC) is currently investigating six reported cases of capillary
leak syndrome in people who were vaccinated with Spikevax, previously known as COVID-19 vaccine Moderna.

These six cases are out of over 61.6 million doses of the Moderna vaccine administered in the European Union and the European Economic Area (Norway, Iceland and Liechtenstein) and since it received authorization in January 2021. The EMA also pointed out that currently there is no evidence of a causal link between the Moderna vaccine and capillary leak syndrome.

The EMA reported that the six cases of the very rare disorder, characterized by leakage of fluid from blood vessels causing tissue swelling and a fall in blood pressure were reported in the EudraVigilance database.

This European database tracks possible adverse effects from registered medications by tracking medical events that have been observed following the use of a medicine. These events are not necessarily related to or caused by the medicine.

"Information on suspected side effects should not be interpreted as meaning that the medicine or the active substance causes the observed effect or is unsafe to use," EudraVigilance says on its site. "Only a detailed evaluation and scientific assessment of all available data allow for robust conclusions to be drawn on the benefits and risks of a medicine."

The occurrence of a medical event after the administration of a medicine, such as in the case of the six reported cases of capillary leak syndrome after the administration of Spikevax, indicates what the EMA calls a "safety signal."

These safety signals are then used to assess if medication and an adverse side effect could be in any way causally linked.

The PRAC will now evaluate all the available data on Spikevax to decide if a causal relationship is considered likely or not, and will release the data in a future review.

Earlier in the COVID global pandemic, Newsweek reported on the possibility of rare side effects emerging from the introduction and administration of new vaccines for the virus.

Director of the International Vaccine Access Center Executive at the Johns Hopkins Bloomberg School of Public Health William Moss said side effects would not be known when the authorization of vaccines began. This would lead to a monitoring period as researchers and manufacturers, as well as health authorities, track possible side effects.

"Monitoring and reporting those outcomes are critical to assuring trust and confidence in any vaccine," professor of the practice of public health leadership at the Harvard T.H. Chan School of Public Health, Howard K. Koh, said.

"No-one ever stops monitoring the safety of medicines—all medicines not just vaccines—even after trials end and rollout starts. We don't generally expect any long-term side effects of vaccines," an associate professor in the pharmacy department at the University of Reading, U.K., Al Edwards said.

Yet, despite the risk of rare or hitherto unrevealed side effects, the researchers that Newsweek spoke to were clear that the risks of COVID far outweigh them.

"Given that we are in the midst of a pandemic that is not under control in the United States, and this is a potentially deadly infection," Moss concluded. "In my view, the benefits outweigh the risks, particularly for those at high risk of infection and severe disease who will be the first to receive the vaccines."

In response to the investigation into the potential link between capillary leak syndrome and Spikevax, Edwards told Newsweek: "We are still improving our understanding of even very rare side effects of the COVID-19 vaccines, as we always do for any medicines.

"What we also know is the devastating damage that COVID-19 infection can cause in unvaccinated individuals, including quite serious cardiovascular problems. With high levels of infection in many regions, exposure is likely, so the balance remains clear: you are far safer being vaccinated than risking severe covid without."

COVID 19 Vaccination
A stock image of a health worker preparing a dose of a COVID vaccination. The EMA is currently investigating six cases of capillary leak syndrome in people vaccinated with the Moderna vaccine. There is currently no evidence of a causal link between the vaccine and capillary leak syndrome. Irina Shatilova/Getty

UPDATE 11/12/21 11:46 a.m. ET: This article was updated to include comment from associate professor Al Edwards.