Fact Check-mRNA cannot be ‘spread’ from COVID-19 vaccines; mRNA is not contagious and it is destroyed by cells shortly after injection 

A Facebook post has falsely claimed that antibodies found in the saliva of those inoculated with an mRNA vaccine can spread the mRNA and their “reprogrammed cells”. This shows a lack of understanding of how mRNA vaccines work.

The post has been shared hundreds of times since it was written on March 20 (here). It cites an article from News Medical, a website reporting on the latest in medical research (here), which discusses a preprint of a scientific paper about COVID-19 mRNA vaccines (here). The paper specifically investigates the presence of antibodies in the saliva of those who have received an mRNA vaccine.

“Eight days ago. Will those receiving the mRNA nanodevices have the mRNA in their saliva?” the Facebook user initially asks. He then quotes the News Medical article: “’Within 1-2 weeks after receiving the 2nd dose of vaccine, 37 of 37 and 8 of 8 recipients of the Pfizer and Moderna vaccines, respectively, had IgG antibodies against the spike protein in their saliva […] Antibody responses to SARS-CoV-2 mRNA vaccines are detectable in saliva.”

The Facebook user then presents his personal conclusion from reading the article: “Antibodies are in the saliva because that’s also where mRNA-1273 is found, the antibodies are going after the presented spike proteins on cell surfaces. What this means, is those who’ve been vaccinated can indeed spread their reprogrammed cells.”

This is not true. Firstly, it should be noted that the research paper is a preliminary report yet to be peer-reviewed. Secondly, even if antibodies have been detected, this does not mean mRNA is present (here). Finally, the idea that cells interacting with the vaccine can be “spread” would suggest the vaccine recipient becomes contagious – but they do not.

The two mRNA vaccines discussed in the scientific research – Moderna’s mRNA-1273 and Pfizer/BioNTech’s BNT162b2 – contain a small piece of the genetic code of SARS-CoV-2, the virus that causes COVID-19 disease. This piece of genetic code, when injected, instructs human cells to create the unique spike protein that surrounds the virus. It does not contain the live virus, ie: the part that takes over a cell, begins replicating over and over and can be transmitted to other people (here).

After the spike protein is made, the cell destroys the mRNA (the vaccine’s genetic material) (here, here). The newly created spike protein is then displayed on the cell’s surface, which elicits a response from the immune system. The immune system makes antibodies to fight the foreign protein, much like what would happen during an infection (here). The vaccine may also activate killer T-cells to destroy cells that display the spike protein fragments on their surfaces (here).

IgG antibodies are common antibodies that can be detected in a person whose immune system has either responded to COVID-19 itself or has been trained by the vaccine to respond (here, here).


False. The mRNA vaccine cannot be “spread” as it neither contains the live virus, nor is it contagious. Once entering the cell and passing on instructions to make the spike protein, the mRNA is then destroyed.

This article was produced by the Reuters Fact Check team. Read more about our fact-checking work here.