Covid Vaccine Side Effects: What to expect and when to get medical help

  • 1st Revision: Isobel Lester
  • 2nd Revision: Alex Jasnosz
  • 3rd Revision: Ha Nguyen

Get our weekly health related email

Your privacy is important to us. Any information you provide to us via this website may be placed by us on servers located in countries outside of the EU. If you do not agree to these placements, please do not provide the information.

Best Milk Alternative

2020 marked the beginning of the COVID-19 pandemic. Months of extensive research have given us access to a variety of vaccines in the hope of  easing the burden COVID-19 has brought to the healthcare systems.

Vaccination is extremely vital in terms of fighting the pandemic. However, a range of questions regarding the efficacy and side effects created a cloud of doubt - vaccine hesitancy. This article aims to provide a brief overview of the side effects of the most popularly used vaccines.  

Common Side Effects  

Similar to the side effects of most vaccines, the side effects of COVID-19 vaccines are usually moderate and fade away within a few days. Commonly reported vaccine side effects include: 

- Soreness, tenderness, warmth or bruising at the injection site, 

- General muscle soreness,

- Fatigue,

- Mild fever (temperature between 37.5 and 38.3°C), 

- Headache,

- Chills,

- Nausea,

- Vomiting,

- Mild flu-like symptoms.

Uncommon Side effects  

- Enlarged lymph nodes,

- Insomnia,

- Rashes (general and/or the site of injection),

- Hives,

- Facial swelling,

- Temporary facial drooping (Bell’s palsy),

- Decreased appetite,

- Abdominal pain,

- Excessive sweating.

Post injection, the recipient is monitored for 15-30 minutes in the event of adverse allergic reaction (anaphylactic shock). The above mentioned side effects may appear at any point between the administration of the injection and  the next day.

Usually, soreness or mild pain in the arm may start soon after the administration of the injection and systemic side effects such as fever, chills, flu like symptoms and more, may begin to appear 8-12 hours post vaccination. These side effects may last between 1 to 4 days post vaccination. 

Side Effects Explained 

The main goal of a vaccine is to create an immune response to the virus, to  provide the body with a route required to fight it, in case of a later infection.  This is done by introducing a harmless amount of the virus into the body.

The common mild side effects are not a cause of concern - it is the body’s way of showing that the vaccine is working the way it should and is creating the desired immune response. Essentially, the body weakens itself, in order to make itself stronger. 

The soreness and redness at the site of injection is a local reaction of the muscle since the vaccine is intramuscular, meaning the liquid in the syringe is administered straight into the muscle. Lymph node enlargement is common post vaccination of any kind and is a sign that the body is producing antibodies required to fight infections, therefore you should not be concerned. 

The first dose of the vaccine makes the immune system recognise the injected material as foreign, causing a response throughout the body. However, the second shot creates a larger immune response, as a result of which, the side effects may be more profound. This prepares the body to fight the COVID-19 virus. To conclude, the common side effects are not a cause of concern, but a sign of the desired immune response.

Precautions to reduce side effects of the vaccine 

It is advisable to wait after receiving the vaccine to assess the severity of side effects. Commonly used pain reliefs such as paracetamol are usually the best way to relieve the mild symptoms (headaches, body aches, fever and chills). There is no known benefit of taking any medication pre-vaccination to reduce the post-vaccine symptoms.

Treating the side effects 

Mild pain and discomfort are common after vaccination. To alleviate this, painkillers like paracetamol or non-steroidal anti-inflammatory drugs (ibuprofen), can be useful. This should be discussed with your healthcare provider.

A cooling compress can be useful to reduce soreness and swelling at the injection site. It is recommended to keep the arm mobile to prevent further discomfort.  

Antibody test after vaccination  

Antibody testing may not be useful in terms of measuring one’s immunity  towards COVID-19 post vaccination. Antibody tests are useful in measuring the immunity post infection by COVID-19.

The vaccine involves the injection of a small amount of the virus into the body to build an immunity, as a result the immune response may not be sufficient enough to be detected. Moreover,  it takes time for the vaccine to provide immunity.  

When to seek help

Healthcare provider should be contacted in the following situations: 

  • Side effects persisting longer than 4 days post vaccination,
  • Increase in redness or soreness at the site of injection over a period of  24 hours (may be a sign of an infection),
  • Severe headache that cannot be relieved with painkillers,
  • Headache coupled with any of the following: blurry vision, drowsiness,  confusion, difficulty with speech, weakness, seizures or drowsiness,
  •  Rash with bruises and/or bleeding under the skin other than the site of  injection,
  • Shortness of breath,
  • Abdominal pain,
  • Chest pain,
  • Leg pain and/or swelling of the limbs,
  • Irregular heartbeat,
  • Swelling of the face, lips or throat,
  • Hives or rash,
  • Weakness and paralysis in the extremities on both sides which may progress to the chest and face (Guillain-Barré Syndrome),
  • Rapid swelling of the limbs due to fluid leakage from small blood vessels  (Leak capillary syndrome).

Manufacturer-specific side effects  

Pfizer-BioNTech and Moderna 

They are double dose vaccines with reported common side effects after  the second dose. These vaccines incorporate mRNA technology. mRNA (genetic material) of a part of the virus degrades in the body after being presented by the innate immune cells to the adaptive immune cells, which in turn make antibodies against it.

There have been some reports of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) after the second dose, primarily in adolescents and young adults. Therefore it is vital to pay attention to side effects that involve heart flutters, irregular heartbeats, chest pain, shortness of breath and/or pounding heart. 

Janssen (Johnson & Johnson) 

Rare cases of TTS or thrombocytopenia syndrome (a severe blood clotting  disorder and low blood platelet counts) have been reported. However, the risk of this is extremely low. There is also a slight risk of developing an autoimmune neurological Guillain-Barré syndrome, with symptoms developing up to 42 days post vaccination.  

Oxford-AstraZeneca and Serum Institute of India  

There is a low risk of developing blood clots as well as Guillain-Barré syndrome.  

It is vital to note that an individual is more likely to develop Guillain-Barré syndrome after a viral infection (including COVID-19), as compared to developing it post vaccination. 

Abnormal mammograms post vaccination  

A mammogram is a screening procedure to check for breast cancer. Since the  vaccine urges the body to produce an immune response, in a small number of  the population, lymph nodes may enlarge.

This may result in abnormal mammogram results appearing, like breast tumours, where in reality the abnormalities are the desired immune response to the vaccine. It is advisable to schedule a mammogram before the first dose of the vaccine or six weeks after the second dose, giving the enlarged lymph nodes enough time to return to their normal size. 

Maternity and vaccination 

COVID-19 vaccines are recommended for pregnant women and breast feeding  mothers. Pregnant women and non-pregnant women showed similar mild,  common side effects post vaccination. Administration of the vaccine is  reported to have no effect on increasing the risk of premature births,  miscarriages, still births and/or congenital abnormalities. 

There is no  specific time during the pregnancy to receive the vaccine, however in case of a double dose vaccine, it is recommended to receive both the doses before the third trimester or at the latest, before giving birth. This can be attributed to the high risk of serious illness and severity of  symptoms if the mother contracts the virus at this stage. 

Vaccination is also safe for breastfeeding mothers as there is no credited mechanism that can allow for the passage of any of the vaccine components from the mother to the baby. Women who are planning on getting pregnant do not need to change their plans due to scheduled COVID-19 vaccination.

Women seeking in vitro fertilisation (IVF) treatments may experience slightly more severe side effects of the vaccine due to the IVF drugs and vaccine cross-reacting. It is advisable to postpone certain procedures such as embryo collection in order to minimise discomfort.

Risk of COVID-19 after vaccination  

The vaccination does not completely prevent one from contracting COVID-19,  upon exposure to the virus that causes it. Individuals can still contract the virus. The role of the vaccine is to reduce the severity of the symptoms if an individual were to contract the virus, and give it less opportunity to overpower the host’s body.  However, it is still important to comply with local government measures set in place with regards to preventive measures against COVID-19. 

Differences in side effects 

The side effects of the vaccine may vary from person to person. Younger  individuals are more likely to show the side effects as compared to the older or elderly population. This can be due to the fact that a stronger immune system will show more profound side effects as compared to comparatively weaker ones, as the side effects are a summation of the good functionality of the immune system. 

Hormones are believed to play a certain role in the severity of the side effects. Testosterone may reduce inflammation and subsequently, the associated side effects.

Testosterone is present at a significantly higher level in males than females, causing a difference in the exhibition of the side effects. Individuals with chronic inflammatory diseases like rheumatoid arthritis (RA), inflammatory bowel disease (IBS) or multiple sclerosis (MS), or individuals consuming immunosuppressant drugs, may experience milder side effects due to a reduced immune response attributing to their condition(s).

Overall, side  effects should not be considered as a measure of the efficacy of the vaccine. Most of the vaccinated population will get the required immunity no matter the presence, absence or magnitude of the side effects.  

COVID 19 vaccine myths  

In an age of digital media and news outlets filled with clickbait titles, misinformation can lead to mass spread of false knowledge, increased  vaccine hesitancy, and reduced vaccination rates. Vaccine hesitancy paves way for  the increase of the spread of the COVID-19 virus. Some of the common myths regarding the COVID-19 vaccines are:

  • Contracting COVID-19 exempts one from taking the vaccine:
    • People who  have been infected with COVID-19 do have antibodies produced on  account of fighting the infection, however there is no guarantee in terms of the period of protection from these antibodies providing natural immunity. Your antibodies may also not offer protection from different strains of COVID-19. Therefore it is advisable to get vaccinated in order to achieve broader adaptive immunity against COVID-19.
  • Administration of the COVID-19 vaccine can give one COVID-19:
    • The role of the vaccine is to mimic an immune response that would occur in case  of exposure to the virus causing Covid-19, via cellular mechanisms. The  vaccine allows the immune system to prepare for virus identification and fights against the virus rather than causing an infection. 
  • The components of the COVID-19 vaccine are controversial:
    • Most of the  Covid-19 vaccines primarily have safe ingredients such as fats, salts, sugars and chemical compounds in a safe amount. It does not contain egg, meat, gluten, implants, microchips or tracking devices.  

Vaccination is extremely vital in terms of protection and building up an  immunity to fight COVID-19. If you have not been vaccinated please contact your local healthcare provider to arrange an appointment. This is the primary exit route for ending the pandemic that has ravaged the world for almost two years.

Get our weekly health related email

Your privacy is important to us. Any information you provide to us via this website may be placed by us on servers located in countries outside of the EU. If you do not agree to these placements, please do not provide the information.

Best Milk Alternative
[optin-monster-inline slug="yw0fgpzdy6fjeb0bbekx"]
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

Get our health newsletter

Get daily health and wellness advice from our medical team.
Your privacy is important to us. Any information you provide to this website may be placed by us on our servers. If you do not agree do not provide the information.

Ishana Gole

Master of Science - MS, Bioscience Entrepreneurship, UCL (University College London)
Ishana is a Biomedical Science student with a keen interest in neuroscience and past experience in online consulting, marketing and advertising.

Leave a Reply

Your email address will not be published. Required fields are marked * presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
Klarity is a citizen-centric health data management platform that enables citizens to securely access, control and share their own health data. Klarity Health Library aims to provide clear and evidence-based health and wellness related informative articles. 
Klarity / Managed Self Ltd
Alum House
5 Alum Chine Road
Westbourne Bournemouth BH4 8DT
VAT Number: 362 5758 74
Company Number: 10696687

Phone Number:

 +44 20 3239 9818