Why do some people get "rare" side effects of Corona vaccines?


Why do some people get "rare" side effects of Corona vaccines?


Vaccines are safe and effective for the vast majority of recipients. but there is a need to understand the causes of rare side effects that may affect a very small number of recipients.

With the successive developments associated with the AstraZeneca vaccine, and the controversy that it raised about its cause of blood clots(coagulation) in some recipients, questions arise about the "rare" side effects that Corona vaccines cause in general with some recipients of different vaccines.


The European Medicines Regulatory Authority has renewed its defense of the vaccine, assuring that its risks are very rare, and they said on Wednesday, that blood clots should be included as one of the "very rare" side effects of the AstraZeneca anti-corona virus vaccine, but confirmed that the benefits of the vaccine still outweigh the risks.

For its part, the World Health Organization announced, on Wednesday, that the link between the AstraZeneca vaccine against the Coronavirus and the emergence of a rare form of blood clots is "possible but not certain."


WHO experts in the field of vaccines said in a statement, "Specialized studies must be conducted in order to fully understand the possible link between vaccination and possible risk factors," noting that these phenomena are "very rare although they are worrisome" noting that more than 200 million people have received the AstraZeneca vaccine. Oxford.

Side effects of vaccines

Vaccine scientist Catherine Edwards of Vanderbilt University School of Medicine in Nashville, Tennessee, says public health officials must strike a "fine balance" when reporting risks of rare side effects compared to the risks of COVID-19. Doctors have some concerns or concerns about the possibility of raising a state of hesitation about receiving vaccines, which has already increased in some societies. At the same time, it is important not to rule out the possibility of rare but severe side effects until researchers can prove the relationship between vaccines and the occurrence of those side effects, a process that can take years, according to Nature.


The damage or side effect can be directly related to when a particular vaccine is received. For example, an early version of the polio vaccine, which used a weak form of the virus to generate immunity, caused approximately 1 person out of every 2.4 million who got the vaccine to become ill.


In this context, Dr. Edwards explains that the virus strain used in the vaccine could have been isolated from the spinal fluid in these cases, so it was clear that the vaccine caused the disease.


And Dr. Edwards adds that these types of tests may not be performed on all possible side effects, either because specific biomarkers are necessary to perform the test, or because such tests may be impractical.


She says side effects, at least initially, are only related to their timing, as when a person receives a vaccine and then experiences side effects at some point afterward, this makes it particularly difficult to establish whether what they were exposed to was actually the result of receiving the vaccine. Especially when the reaction occurs days or weeks after receiving the same vaccination.


Dr. Edwards explains that to verify a link between receiving the vaccine and the symptoms that can occur to a person, Researchers are conducting a study to determine the incidence of side effects in vaccinated compared to unvaccinated groups. Hence, they also need to identify the mechanism that could be causing it.

Very rare cases

Regarding Covid-19 vaccines, Professor Hilda Bastian, an independent scientist specializing in evidence-based medicine in Victoria, Australia, says that the vaccines that are currently being rolled out in clinical trials have been tested in thousands of participants before governments allow them to be widely used.


Clinical trials were designed and prepared to ensure answers to very common questions related primarily to efficacy and to assess the rate of general side effects, such as pain at the injection site or headache, and therefore many vaccine specialists, who were surveyed, were keen on Emphasize that COVID-19 vaccines are safe and effective for the general public of recipients.


But none of the clinical trials, even the largest, were designed to detect extremely rare side effects, which could affect less than one case per 10,000 vaccine recipients, according to Professor Bastian, who indicated that because hundreds of millions of people are vaccinated Currently against the COVID-19 virus, it stands to reason that extremely rare side effects, such as severe allergic reactions or blood clots, could start showing up in reports.


Current challenge

The challenge now is to find out which side effects are actually related to the vaccine. And then the US National Institute of Allergy and Infectious Diseases began organizing clinical trials to understand the risks of allergies that could result from receiving Covid-19 vaccines, which are based on mRNA technology, which is the vaccine manufactured by Pfizer in the United States, and Biontech in Germany, which is related An average of five cases of a severe allergic reaction per million doses, as well as the vaccine produced by Moderna in Cambridge, Massachusetts, which is associated with an average of three cases per million doses, but it seems that the infected are people who already suffer from a history of allergies.


Professor Stacy Jones, a specialist in allergies and immunology at the University of Arkansas for Medical Sciences in Little Rock, and her colleagues are leading a study in one of 30 sites across the United States of America, to further understand about the rate of allergic reaction among those who already suffer from a history of allergies, Compared to a control group.


Professor Jones says that allergic reactions are "extremely rare", but that the results of the study are expected to allow identification of the people most at risk and the type of risk "so that doctors can provide better advice."



Better monitoring


A better understanding of the safety of the vaccine can be obtained from monitoring systems that collect data on rare side effects, accompanied by explanations of each of the rates of infection among those with pre-existing allergies and after receiving the vaccine, from electronic health records without relying on what is reported directly from the persons themselves.


In this regard, Dr. Jones stresses that the combination of active surveillance and targeted clinical trials will pave the way to ensure the safety of current Covid-19 vaccines, in addition to achieving a benefit at the level of public health policies, including determining the safety of receiving booster vaccines or annual vaccines, which can They are necessary throughout the duration of the pandemic and beyond.





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