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How should you feel after your Covid vaccine? An immune doctor explains

April 16th 2021 / Dr Jenna Macciochi / 0 comment

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Whether you’ve had the Covid vaccine already or are waiting patiently, chances are you’ve heard about people’s varying reactions to the injection. Here Dr Jenna Macciochi explains what the different reactions mean

There is a lot of discussion surrounding vaccination at the moment thanks to the ongoing Covid mass vaccination programme, so it's natural to have some questions about the Covid vaccine and what the short-term side effects mean, especially as they can vary from person to person.

Why might I feel ill after the Covid vaccine?

You may feel some symptoms, including fatigue, chills, headaches, fever and joint pain, redness around the injection site or tiredness in the hours and days after your Covid vaccine. This is simply your immune system responding to the viral pieces. It’s known as ‘vaccine reactogenicity’. Although unpleasant, any symptoms arising in the 48 hours following a vaccine are actually a sign of your immune system doing its job. It's a sign that your body is creating an immune response and that the vaccine is working. These side effects don’t mean you have an infection, nor are you contagious.

What are the most common side effects of the coronavirus vaccine?

According to the NHS, the most common side effects are a sore arm where the needle went in, feeling tired, a headache, feeling achy, feeling or being sick. You may get a high temperature or feel hot or shivery one or two days after having your vaccination. You should tell vaccine staff beforehand if you’ve ever had a serious allergic reaction. If you have a high temperature that lasts longer than two days, a new continuous cough or a loss or change to your sense of smell or taste you may have coronavirus (meaning you were infected before the vaccine). Stay at home and get a test.

If you have symptoms starting from around four days to four weeks after being vaccinated such as severe headaches (find out more on the NHS website) you should call 111.

Why do some people have reactions to the Covid vaccine?

We all vary in our immune response to infections. This is something that has long been known but now it’s much more talked about since all eyes have been on Covid, where we’ve seen anything from severe disease to people without symptoms among those who have the virus.

We also see this variation in reactions with vaccination responses but to a lesser degree as vaccines are generally much more targeted and controlled in the way they activate the immune system.

Why do people react differently to the Covid vaccine?

Studies show that a significant factor in the way we respond to any vaccine relates to genetics, age, gender and any underlying health conditions. We call these ‘vaccine response co-factors.

Other co-factors can be geographic location, specifically latitude – in the case of certain tuberculosis vaccines, for example, some studies have shown that the greater distance you live from the equator associates with a better vaccine response, by as much as 41 per cent.

Your socioeconomic conditions, climate, exposure to sunlight, diet and nutrition, pre-existing immunity/exposure to microbes from the same family as the vaccine all have an impact too.

I had no reaction to my first Covid vaccine, will I be fine after the second dose too?

In general, side effects tend to be worse after the second dose except in people who have been infected with Covid in the past. People in this situation are almost twice as likely to have a reaction to the first dose because it is essentially acting as the second dose.

Should I take painkillers before the Covid vaccine to avoid side effects after?

You shouldn’t take any specific medications such as painkillers and antipyretics (anti-fever e.g., paracetamol) ahead of your appointment in an attempt to prevent a reaction. Studies show that taking antipyretics before or at the time of receiving a vaccine may mildly decrease antibody production by preventing the immune system from doing its job (although the evidence shows that they still stay within protective range).

In general, it is safe to let a low-grade fever run its course. The best thing to do is tune in to how you feel and rest.

If I don’t have any side effects from the Covid vaccine does it mean the vaccine isn’t working?

At this stage, it’s a possible hypothesis that more side effects would indicate a more robust immune response to the Covid vaccine. Generally, women and younger people report worse symptoms and the reasons for this are currently unclear.

As it stands we can't infer anything about how well your immune system has been primed from your post-vaccination symptoms alone. So far there is no published evidence that having no reaction means reduced protection but there are a few interesting observations. For example, the Medicines and Healthcare products Regulatory Agency (MHRA) which monitor vaccine safety in the UK, states that one in ten vaccine recipients experience some reaction to one of the three UK approved Covid vaccines but there is no major difference between them in terms of reported side-effects.

Published data from the AstraZeneca Covid vaccine trial showed all the volunteers' immune systems responded to the jab by producing similar levels of antibodies, whether or not they experienced common side-effects. Even though reduced reactions were recently reported in older adults to the Covid vaccine, they did still make antibodies within the protective range.

Dr Jenna Macciochi is an immunologist and brand ambassador for supplement and well-being brand Healthspan. Based in Brighton, Jenna is a lecturer at Sussex University and a qualified fitness instructor. She is a mother of five-year-old twins and a keen home cook, creating recipes inspired by her farm-to-table Scottish roots and capturing her Italian heritage.

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