COVID-19 mRNA vaccines help our bodies create spike proteins, which generate an immune response to fight the COVID-19. There is no evidence that mRNA vaccines create other proteins, and there is no evidence that mRNA vaccines cause autoimmune diseases. 

mRNA vaccines, or “messenger RNA” vaccines, are a type of vaccine that does not carry an inactivated or weakened pathogen (a bacteria or virus) into our body like most vaccines do. Instead, they carry information in the form of genetic code, which instructs the cells in the body to create a spike protein or a part of a spike protein. Soon after making the protein, our cells break down the mRNA instructions and get rid of it. Next, the cell displays the protein piece on its surface and our immune system recognizes that it’s foreign and triggers an immune response. This targeted response includes the deployment of antibodies, proteins created by the immune system to find and remove the virus from the body.

Autoimmune diseases, such as lupus and rheumatoid arthritis, occur when the immune system attacks itself by being unable to recognize regular cells from foreign cells. There is evidence that COVID-19 infection can, in some (particularly severe) cases, lead to autoimmune diseases or hyperactive autoimmune states. However, there is no evidence that mRNA vaccines put the immune system in this hyperactive state or lead to autoimmune diseases.

A 2018 journal review on mRNA vaccines listed autoimmunity among possible adverse reactions; however, one of the co-authors has noted that this is not a concern for the COVID-19 vaccines because they use a new kind of modified RNA that has been in use for over 5 years. Neither the Pfizer nor Moderna vaccine trials found autoimmune responses as side effects in participants they studied. 

While the U.S. Centers for Disease Control and Prevention have noted that individuals with existing autoimmune disorders may receive the vaccine, we are currently lacking robust safety data given that trials did not include specific data about these populations. Scientists and public health professionals will continue to closely monitor vaccinated individuals to ensure that autoimmune disorders can be entirely ruled out as a side effect of COVID-19 vaccines.

There a few main data points that suggest that COVID-19 infection might trigger autoimmune response: 1) a University College of London Hospital study of 43 patients previously infected with COVID-19, which found that 8 participants developed Guillain-Barre syndrome and nine developed acute disseminated encephalomyelitis, both autoimmune diseases; 2) reports of hemophagocytosis in affected patients (when immune cells that aren’t working properly “eat” other cells); 3) elevated cytokine levels in affected patients (especially those with severe COVID-19), and 4) beneficial effects of immunosuppressants in affected patients. 

Several clinical and laboratory irregularities, such as renal dysfunction and elevated CRP (a measure in the blood that marks inflammation) have also been observed with COVID-19 as they are with some immune-mediated events such as cytokine storm.

These data indicate that there is a probable, but under-explored causal link between COVID-19 (particularly severe cases) and autoimmunity. Further research is needed to better understand this potential link. This link has contributed to the ongoing spread of unsubstantiated claims that Pfizer and Moderna’s COVID-19 respective mRNA vaccines are likely to lead to autoimmune disorders.