What is the ADE phenomenon and why is it not related to the SARS-CoV-2 vaccine?

At an online conference organised by Autonomous University of Querétaro (Mexico), a women identified as Karina Acevedo, an immunologist and researcher, claims that the vaccines developed against SARS-CoV-1 caused the death of laboratory animals on which the antibody-dependent amplification of the infection were tested (a phenomenon known as ADE) and that there are no proofs that injections against SARS-CoV-2 are safe in this sense. This is FALSE. Although it is true that some experimental vaccines against SARS (that were never used in humans) cause this adverse effect of the immune system in some laboratory animals, for the moment no confirmed cases of ADE are known for humans and animals since vaccines against SARS-CoV-2 started to be developed.

"11 independent animal studies with vaccines against SARS-CoV-1 had found evidence of immunopathology, regardless of the vaccine type, when animals were exposed to the virus months later. All of them died due to a very severe liver inflammation. Their conclusion was that ADE can also occur with vaccines against SARS-CoV-2, but no clinical data are available yet".

ADE is a rather paradoxical phenomenon: it makes the antibodies of our immune system, which are supposed to fight infections in the body, to turn against it, even worsening the disease. It is as if the immune system suddenly betrayed us. Explained in a scientific manner, ADE occurs “when the antibodies generated against the first virus —for instance, dengue serotype 1— are not able of neutralising the virus causing the second infection —for instance, dengue serotype 2—, but upon attaching to it they worsen the outcome of the infection”, explains Adelaida Sarukhan, immunologist and scientific writer at the Barcelona Institute for Global Health (ISGlobal, in Catalan) to Verficiat, who insists in that “sufficient clinical data are available to deny this assertment” from Acevedo.

The ADE phenomenon has previously been observed with other viruses such as dengue or the respiratory syncytial virus. During the research phase of vaccines against SARS-CoV-1, a coronavirus that emerged in China in 2003 and eventually spread in about 30 countries, it also happened that laboratory animals that were given some experimental vials died due to this phenomenon.

This has not been the case for SARS-CoV-2 vaccines. “On the contrary, clinical trials and large-scale vaccination —hundreds of millions of vaccinated people all over the world— clearly indicate that vaccines protect very effectively against severe disease forms, even in people infected with the new variants”, indicates Sarukhan.

The previous experience with SARS-CoV-1

Acevedo mentions during her presentation a meeting that took place on 12-13 March 2020 where, in the face of SARS-CoV-2 spread, experts in immunology and vaccinology presented previous experience with vaccines against the previous coronavirus, which had caused the risk of ADE in some animals.

The reason scientists considered it a risk of covid-19 vaccines stems from the fact that is was already seen with a candidate SARS vaccine tested in animals —but not in all, as Acevedo assures—: “Instead of protecting, the vaccine worsened the disease in some of the vaccinated animals”, describes the expert. The reason, in part, seemed to be “the antigen used for the vaccine, the N protein instead of the S protein, which is the one used in the case of SARS-CoV-2”.

All covid-19 vaccines use the S protein. This previous experience with SARS-CoV-1 served as a precedent regarding which antigen should be used in the development of these new injections. Even so, Sarukhan concludes, “any signs of ADE in vaccinated animals were closely surveyed”.