There’s no evidence Covid-19 vaccines make the disease worse

9 June 2021
What was claimed

Evidence is growing that Covid-19 vaccines may worsen the disease in some recipients because antibodies developed as a result of the jab can end up enhancing disease rather than protecting against infection.

Our verdict

Antibody dependant enhancement is a rare but genuine risk when it comes to creating new vaccines. There is good evidence that this does not occur with the current Covid-19 vaccines in use, from animal studies, large human trials, and real world data from people who have received the vaccine.

An article on the website Conservative Woman has set out concerns that the Covid-19 vaccines may worsen Covid-19 in some vaccinated people, through a process known as “antibody dependant enhancement”. 

Antibody dependant enhancement (ADE), which the article describes, is a real phenomenon, and a genuine consideration during the creation of any vaccine,  but the evidence shows that this is not occurring with Covid-19 vaccines that are currently in use. 

What is antibody dependent enhancement? 

ADE is a mechanism whereby antibodies generated during a previous immune response (either from getting the infection or being vaccinated against it) don’t stop you getting ill again and, instead, there is an exacerbation of the immune response and a worsening of the disease. 

Work to fully understand how this occurs is ongoing, but it is thought to occur through two main mechanisms: either the pre-existing antibodies facilitate the entry and replication of the virus in the body’s cells, or antibodies cause the immune system to ‘overreact’.

ADE is very rare, however some infections, like dengue fever are known to cause the phenomena. 

Historically some vaccines (which are no longer used, or which can only be used in very particular circumstances) have caused ADE.  For example, a respiratory syncytial virus vaccine designed in the 1960s (the clinical trial was stopped and it hasn’t been used), a measles vaccine designed in the 1960s (not the MMR vaccine in current use) and a dengue fever vaccine introduced in 2016 (which can now only be used in children over the age of 9 who have already had prior infection). 

There was also some prior evidence from lab and animal studies for the coronaviruses SARS (not SARS-CoV-2, which causes Covid-19) and MERS which showed that ADE-type reactions sometimes occurred. This was not a consistent finding, but this knowledge allowed scientists to be aware of the possibility that this could potentially occur when designing the Covid-19 vaccines.

We’re not seeing ADE with Covid-19 vaccines

The evidence to date does not suggest that the Covid-19 vaccines cause ADE. 

Professor Penny Ward, chair of the Education and Standards Committee at the Faculty of Pharmaceutical Medicine told Full Fact that ADE is “a theoretical concern with vaccines and has been observed in the past with [the respiratory syncytial virus] vaccine”. 

She added: “Following that experience, the mechanisms by which this is caused were worked out, and as a result it was possible to investigate this prior to starting human clinical trials. 

“In addition the [Covid-19] vaccines were investigated in animals which were subsequently challenged with SARS CoV2 virus, which confirmed protection against disease and no exacerbation of pathology in animals. 

“Lastly, the size of the phase III trials were large enough to detect a potential for antibody enhanced disease and, as we know this was not observed. Indeed the precise opposite was observed with vaccine[s] being highly protective for symptomatic disease and completely preventing severe disease. This has been confirmed with 'real world data' following introduction of the vaccines into clinical use.”

The Medicines and Health product Regulatory Agency confirmed to Full Fact that antibody dependant enhancement was considered a theoretical risk at the time of initial approval, but there is no evidence that the vaccines cause ADE.

The Conservative Woman article references a paper published in December 2020 in the International Journal of Clinical Practice. The paper argued that Covid-19 vaccine trial participants, and future recipients, should be made aware of the potential risk of ADE, but the study doesn’t suggest that this had actually occurred with Covid-19 vaccines. 

Similarly, the article points to an open letter to international health authorities and vaccine developers from a number of physicians which asked questions about potential vaccine risks, including ADE. Again, the authors do not suggest that there is evidence that ADE has or is occuring with the Covid-19 vaccines.   

The Conservative Woman piece also talks about concerns over deaths after vaccinations in Gibraltar. We have previously written about how there was no evidence these deaths were related to the vaccine. 

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