According to Gavi, the global vaccine alliance, side effects may be more common if you have already been infected by the virus in the past, with your immune system being conditioned to respond to it
Millions of people across the world have been vaccinated against Covid-19, and many more are to follow.
A lot of the people inoculated have experienced minor side effects, including mild fevers, headaches, sore bodies and fatigue. These reactions are normal, and usually arrive one to two days after inoculation. They are also signs that the vaccine is working.
However, many people do not have side effects as well.
According to Gavi, the global vaccine alliance, side effects may be more common if you have already been infected by the virus in the past, as your immune system is conditioned to respond to it.
Vaccines help the immune system recognize and respond to pathogens by initiating a disabled form of the virus, viral proteins or genetic instructions to make the proteins. They work this way so that the next time your body is introduced to a similar or identical virus, your body is capable of fighting it off.
This process kickstarts immune reactions that would have been implemented when encountering the actual virus.
First, the immune system’s “first responder” cells release chemical messages that bring other immune cells to the injection site. Blood vessels also thin, assisting immune cells to transport themselves to the site.
The immune cells then form an adaptive response, including antibody producing B cells and immune T cells which help to destroy infected cells.
After the process takes place, some of these reactions trigger side effects or symptoms that feel like symptoms from a real infection.
This process works to ensure that the next time a person encounters a pathogen, the immune system is equipped to provide the responses faster and more efficiently, as they are already familiar with it.
This is why people who have already been infected with Covid-19 may experience more side effects. It is nothing to worry about, and is a very similar experience to receiving the second dose of the vaccine, where the immune system was already prepared to recognize the pathogen.
Two small studies conducted recently have suggested that people who have already been infected may only need one dose of the mRNA vaccine. However, studies to follow up the claims are required to confirm the hypothesis, and that the existing immune response sustains over time.
One of the studies also observed the number of reactions after the first dose of the Moderna or Pfizer vaccines. 231 people were studied, and it was found that while symptoms were similar, some side effects such as whole body reactions were more common in people who already recovered from the virus.
The results from this study match the ZOE COVID Symptom Study, which observes the symptoms recorded by participants via a smartphone app. The study has four million participants, and found that recovered patients were twice as likely to experience more than one side effect from the Pfizer-BioNTech vaccine, compared to participants who never had the virus.
Common symptoms included fatigue (9%), headache (8%) and chills or shivers (4%), mostly reported during the two initial days after inoculation.
The study also found that people under the age of 55 were more susceptible to the symptoms, and were more likely to experience side effects after the second dose of the vaccine.
In most cases, only 3% of people experienced side effects three days after inoculation.
Gavi is a global vaccine alliance that helps vaccinate the world’s children against deadly and debilitating infectious diseases. Core partners of the alliance include the World Health Organization (WHO), UNICEF, the World Bank and the Bill & Melinda Gates Foundation.