Are there long-term side effects caused by mRNA COVID-19 vaccines? How do we know?


Are there long-term side effects caused by mRNA COVID-19 vaccines? How do we know?


The medical and scientific community is confident in the long-term safety of the mRNA COVID-19 vaccines.

According to the USA Centers for Disease Control, “Researchers have been studying and working with mRNA vaccines for decades. mRNA vaccines have been studied before for flu, Zika, rabies, and cytomegalovirus (CMV). As soon as the necessary information about the virus that causes COVID-19 was available, scientists began designing the mRNA instructions for cells to build the unique spike protein into an mRNA vaccine." In addition, cancer research has used mRNA to trigger the immune system to target specific cancer cells. Decades of studying mRNA have shown no long-term side-effects.

According to the Children’s Hospital of Philadelphia , the vaccine is not expected to have long-term negative effects for a few reasons:

  • First, most negative effects occur within 6 weeks of receiving a vaccine, which is why the FDA asked the companies to provide 8 weeks of safety data after the last dose.
  • Second, the mRNA in the vaccine breaks down pretty quickly because our cells need a way to stop mRNA from making too many proteins or too much protein.
  • But, even if for some reason our cells did not break down the vaccine mRNA, the mRNA stops making the protein within about a week, regardless of the body’s immune response to the protein.

In addition, the medical and scientific community is confident in the vaccine’s long-term safety, because of the track record of Canada's vaccine approval and B.C.'s safety monitoring system. Overall, this means that the end data and safety tests are exactly the same as other vaccines that have been approved in Canada. The safety monitoring system in Canada happens both passively and actively.

  • Passive safety monitoring happens when anyone with a significant reaction to any vaccine reports it to their healthcare provider which is then reported to the BCCDC, Health Canada and all the way up to the World Health Organization. This information is shared globally in a timely way to flag for other countries any emerging and urgent concerns.
  • An example of active safety monitoring is the nurses across Canada who are actively reviewing patients’ charts as part of the IMPACT (Immunization Monitoring Program ACTive). This is a pediatric hospital-based national active surveillance network for adverse events in children following immunization, vaccine failures and selected infectious diseases that are, or will be, vaccine-preventable.

Canada’s system has proven time and again that the data necessary to get through the approval process is sufficient to prove safety, even for the long-term.

Date last reviewed: 
Wednesday, Jul 21, 2021