It’s Normal to Have Side Effects from Covid-19 Vaccine. Why?

Vaccines are designed to give you immunity without the dangers of getting the disease. It’s common to experience some mild-to-moderate side effects when receiving vaccinations. This is because your immune system is instructing your body to react in certain ways: it increases blood flow so more immune cells can circulate, and it raises your body temperature in order to kill the virus.

How does the Vaccine Work?

vaccine side effects

There are a few main novel coronavirus (COVID-19) vaccines.

The two-dose vaccines currently approved for use in U.S. are messenger RNA (mRNA) vaccines produced by Pfizer and Moderna. The vaccine includes a fragment of the mRNA that encodes for a certain portion of the coronavirus’ spike protein. When the vaccine is given to us, our cells make that protein – a fragment of it – and then our bodies build an immune response to the protein.

The single-dose Johnson & Johnson vaccine is a DNA vaccine, but it delivers the same product in the end as the mRNA vaccine produced by Pfizer and Moderna. This new DNA vaccine allows the body to have an immune response against the spike protein, and ultimately, an immune response to infection. On April 13, the FDA and CDC issued a recommended pause in the use of Johnson & Johnson vaccines, but that recommendation was lifted on April 23 following a thorough safety review. However, UC Davis Health has continued our paused use of the Johnson & Johnson vaccine.

The other vaccine produced by Oxford/AstraZeneca is similar. It’s in use in the United Kingdom and India. It includes a non-replicating adenovirus vector that has a fragment of the spike protein, which causes us to have an immune response.

Common Side Effects of COVID-19 vaccines

Reported side effects of COVID-19 vaccines have mostly been mild to moderate and have lasted no longer than a few days.


Typical side effects include,

  • Pain at the injection site
  • Fever
  • Fatigue
  • Headache
  • Muscle pain
  • Chills
  • Diarrhoea.

The chances of any of these side effects occurring after vaccination can differ according to the specific vaccine.

Less Common Effect

Upon receiving the vaccine, a person should be requested to stay for 15–30 minutes at the vaccination site so health workers are available in case of any immediate reactions. Individuals should alert their local health providers following vaccination if they experience any unexpected side effects or other health events – such as side effects lasting more than three days.

Less common side effects reported for some COVID-19 vaccines have included severe allergic reactions such as anaphylaxis; however, this reaction is extremely rare.

National authorities and international bodies, including WHO, are closely monitoring for any unexpected side effects following COVID-19 vaccine use.

Long-term Side Effects

Side effects usually occur within the first few days of getting a vaccine. Since the first mass vaccination programme started in early December 2020, hundreds of millions of vaccine doses have been administered.

There have been concerns about COVID-19 vaccines making people sick with COVID-19. But none of the approved vaccines contain the live virus that causes COVID-19, which means that COVID-19 vaccines cannot make you sick with COVID-19.

After vaccination, it usually takes a few weeks for the body to build immunity against SARS-CoV-2, the virus that causes COVID-19. So it’s possible a person could be infected with SARS-CoV-2 just before or after vaccination and still get sick with COVID-19. This is because the vaccine has not yet had enough time to provide protection.

Experiencing side effects after getting vaccinated means the vaccine is working and your immune system is responding as it should.

Vaccines are safe, and getting vaccinated will help protect you against COVID-19.

For Helpful Tips to Relieve Side Effects, click here



The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

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