The most common side effect experienced among those who have received a Covid-19 vaccine has been soreness around the injection site. This was also more frequent among younger vaccine recipients, with 83 per cent of those between 18 and 55 reporting sore arms after receiving the first jab, noted a Pfizer-BioNTech vaccine clinical trial. This compared with 71 per cent of those aged above 55.
Similarly, 87 per cent of people under the age of 65 reported localised pain after the first shot of the Moderna vaccine during clinical trials, compared with 74 per cent of those over 65.
Here are a few reasons why the side effects vary between different groups of people.