COVID-19 vaccines

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COVID-19 is an infectious disease, caused by a coronavirus that was first detected in China at the end of 2019. Vaccines to protect people against this new disease first became available in early December 2020.

The majority of people in the UK are now vaccinated. A high proportion will also have developed additional immunity through having COVID-19 disease. The strong immunity among the UK population means that the severe form of COVID-19 disease that was seen in the first 18 months of the pandemic is now very rare in the UK.

This is why there is now a more targeted approach to vaccination that aims to protect those who have underlying health conditions or frailty. This puts them at high risk of getting seriously ill, or dying, when they develop a viral infection like COVID-19.  

Globally, a number of different vaccines for COVID-19 have been trialled, shown to be safe and effective, and approved by regulators. These are monitored on an on-going basis.

In the UK, the Medicines and Healthcare products Regulatory Agency (MRHA) has approved six vaccines, although these are not all in use currently.

The names of the six approved vaccines are:

  • Spikevax (Moderna)
  • Comirnaty  (Pfizer/BioNTech)
  • Nuvaxovid  (Novavax)
  • Vaxzevria (AstraZeneca/Oxford)
  • Janssen COVID-19 Vaccine (Johnson & Johnson)
  • Valneva (Valneva)

All of the vaccines have been shown to be highly effective against severe COVID-19 but the emergence of new variants has meant that the original vaccines are less effective in preventing milder infections caused by these new variants.

COVID-19 vaccines made by Pfizer and Moderna have been updated since the original vaccines and target a different COVID-19 variant. These updated vaccines boost protection well, and give slightly higher levels of antibody against the more recent strains of COVID-19 (Omicron).  These vaccines are currently used in the spring 2024 COVID-19 vaccine campaign.

Novavax’s vaccine is only given to the small number of people who cannot have the Pfizer/BioNTech and Moderna vaccines.


Most people with COVID-19 will only be mildly or moderately ill and won’t require medical treatment, but for older people, or people with certain health conditions, it can be more serious.

Therefore, a spring COVID-19 vaccine will only be offered to those who might develop more serious symptoms of COVID-19. These include; 

  • those aged 75 years and over,
  • those in care homes,
  • those over 6 months of age with a weakened immune system.   

Eligible individuals will be offered an appointment to receive their vaccine between April 2024 and June 2024. Appointments will be offered to those at the highest risk of developing severe symptoms first. 

Booster doses will be offered around 6 months after the spring dose, but this can be given as early as 3 months. 

If you have previously had a severe reaction to a previous dose of a COVID-19 vaccine, you should discuss this with your healthcare provider before receiving the spring dose. 



Over 5.5 billion people had received at least one COVID-19 vaccine around the world by March 2023, providing ‘real-life’ evidence about their safety. 

Like all medicines, vaccines carry a risk of side effects, although not everyone gets them. The COVID-19 vaccines currently approved in the UK have been thoroughly reviewed by the Medicines and Healthcare products Regulatory Agency (the MHRA).

The regulatory team completed a full review of the safety information reported from the vaccines’ trials. This included several months after trial participants received the vaccines. Regulators continue to review any emerging safety data and the health of participants from the original clinical trials is ‘followed up’ for a number of years.

Common siude effects for the Pfizer/BioNTech, Moderna and Novavax vaccines include:

Very common – may affect more than 1 in 10 people:

  • injection site redness, pain and/or swelling
  • tiredness
  • headache
  • chills
  • fever
  • feeling sick

Common – may affect up to 1 in 10 people.

  • diarrhoea
  • nausea
  • vomiting

Uncommon – may affect up to 1 in 100 people:

  • enlarged lymph nodes
  • dizziness
  • itchy skin, rash or hives
  • insomnia
  • excessive sweating and night sweats

Rare – may affect up to 1 in 1,000 people:

  • temporary drooping to one side of the face
  • swelling of the face or other allergic reactions

There have also been very rare cases of heart-related side effects. This includes inflammation of the heart muscle (myocarditis) and inflammation of the lining of the outside of the heart (pericarditis). These can result in breathlessness, palpitations or chest pains. People who experience any of these heart-related symptoms are advised by the NHS either to call 999 or go to the nearest Accident and Emergency department. 

People who are concerned about any reactions that occur after vaccination should consult their doctor.

The vast majority of people can have COVID-19 vaccinations. But the vaccines should not be given to those who have had a previous severe allergic (anaphylaxis) reaction to:

  • a previous dose of the same COVID-19 vaccine
  • an ingredient in the COVID-19 vaccine. 

As with any vaccine, medicine or food, there is a very small chance of a severe allergic reaction. Anaphylaxis is different from less severe allergic reactions because it causes life-threatening breathing and/or circulation problems. Even though it is always extremely serious, it can be treated with adrenaline. Healthcare workers who give vaccines know how to do this.

There were no serious allergic reactions during any of the trials of the COVID-19 vaccines, although they did not include people with known severe allergies. After the Pfizer-BioNTech vaccine was rolled out in the UK, two people suffered anaphylaxis caused by an ingredient in the vaccine. Both already had severe allergies and carried emergency adrenaline pens. 

In general, vaccine-related anaphylaxis is very rare. In the UK between 1997 and 2003 there were a total of 130 reports of anaphylaxis following ALL immunisations – around 117 million doses of vaccines. People who have a known allergy to certain ingredients should inform the vaccinator before receiving a COVID-19 vaccine.

In the UK you can report suspected vaccine side effects to the Medicines and Healthcare products Regulatory Agency (MHRA) through the Yellow Card Scheme. You can also contact the MHRA to ask for data on Yellow Card reports for individual vaccines. See more information on the Yellow Card scheme and monitoring of vaccine safety


Many of the ingredients found in the COVID-19 vaccines can also be found in food. This includes, for example, sugars, acidity regulators, fats, and salts. 

The vaccines do not contain human or animal products. Their ingredients also do not include common allergens, such as latex, milk, lactose, gluten, egg, maize/corn, or peanuts.

Both the Pfizer-BioNTech and Moderna vaccines contain genetic code (messenger ribonucleic acid - mRNA) which instructs our cells to make the COVID-19 spike protein and in turn to stimulate the body’s immune system to create antibodies against the COVID-19 virus. mRNA is created in a manufacturing facility.  

The Novavax vaccine does not contain genetic material, but pieces of spike protein from the virus, again to stimulate the body’s immune system into producing antibodies. It also contains a natural substance from a tree that acts as an ‘adjuvant’, to enhance the body’s response to the vaccine.

None of the vaccines against COVID-19 contain gelatine. And the vaccines currently used in the UK do not contain alcohol.


People who are pregnant, and without immunity to COVID-19 are more likely to become seriously ill and need hospital treatment if they get COVID-19, compared with those who aren’t. In addition, having COVID-19 during pregnancy could result in poor outcomes, such as a baby being born too soon, as well as an increased risk of still birth, high blood-pressure (pre-eclampsia) or an emergency caesarean.

That’s why vaccination, including boosters, is recommended during pregnancy. Pregnant women are currently considered a high risk group.

None of the COVID-19 vaccines contain live coronavirus. This means they cannot infect the pregnant person or their unborn baby.

In the UK, the mRNA vaccines from Moderna and Pfizer/BioNTech are currently recommended as boosters. According to data from around the world from thousands of pregnancies, there has not been an increase in miscarriage, pre-term birth or still birth after a person has been vaccinated.

Getting first vaccinations, or boosters during pregnancy also helps to protect the baby against the disease once they are born but too young to be vaccinated themselves. This is also true of the flu and pertussis vaccines. There is evidence that vaccination during pregnancy may prevent babies from becoming hospitalised from COVID-19 during their first sixth months of life.

It is possible to receive the COVID-19, flu and pertussis vaccines at the same time, although as pertussis has to be done at a specific point during a pregnancy, it may be done at a separate time.


The Pfizer/BioNTech and AstraZeneca/Oxford vaccines were the most widely used vaccines to protect the UK population in 2021. Since then most booster doses have been the Pfizer/BioNTech and Moderna vaccines.  The AstraZeneca/Oxford, Johnson & Johnson and Valneva vaccines are not currently used.

In total, the World Health Organization (WHO) has approved nine different COVID-19 vaccines for use in a public health emergency. This includes the six approved in the UK, along with three more produced by companies in China and India. These met WHO regulatory standards before being added to their emergency list. There are currently around 380 different vaccines at some stage of the research, development, and testing process.

While the existing vaccines protect people against getting seriously ill, they do not reduce the transmission of emerging new variants virus. And with the virus still circulating, there is an ongoing risk of new variants emerging for which existing vaccines will only provide limited protection against infection.

However, it is highly unlikely that the wall of immunity across the population against severe disease will get significantly less.

Developing a vaccine for COVID-19

Even though COVID-19 is a new disease, caused by a novel coronavirus, work to develop vaccines to protect us against this family of coronaviruses began about 20 years ago. Coronaviruses were already a threat to our health.

The clinical trials to test the vaccines were carried out more quickly than normal by overlapping the different trial stages. A trial’s three stages are usually done one after the other.

No stage was missed out in the COVID vaccine trials and the trials were subject to the same strict regulatory requirements as any other vaccine. This video shows how scientists were able to make the AstraZeneca/Oxford vaccine so quickly.


How to make a vaccine in record time


The vaccines that have been approved for use in the UK were tested in trials with over 20,000 people.  In many cases, these trials are larger than trials for other drugs and vaccines which have been licensed.

Please see below for information about how vaccines are developed and how some of the administrative processes were speeded up. With thanks to Nature for permission to use this video.


Vaccines 101: How new vaccines are developed

mRNA vaccines - Pfizer-BioNTech and Moderna

These vaccines each contain the genetic code (mRNA) of the spike protein found on the surface of the SARS-CoV-2 virus. Once inside the body, the spike protein is produced, causing the immune system to recognise it and initiate an immune response. 

This means that if the body later encounters the spike protein of the coronavirus, the immune system will recognise it and destroy it before causing infection.

As there is no whole or live virus involved, the vaccines cannot cause COVID-19 disease. The mRNA is naturally degraded after a few days.

The safety and efficacy of the Pfizer-BioNTech vaccine were assessed in clinical trials of over 44,000 people in six countries: USA, Germany, Brazil, Argentina, South Africa and Turkey.  The trial also showed that the vaccine provides similar protection in people of all ages, races and ethnicities.

The safety and efficacy of the Moderna vaccine was tested in over 30,000 people across the United States, including older people, people from ethnic minorities and those with underlying health conditions.

Viral vector vaccines - Oxford-AstraZeneca ChAdOx1 nCoV-19 and Janssen

Viral vector vaccines work by delivering the genetic code of the SARS-CoV-2 spike protein to the body’s cells, similar to the mRNA vaccines.

Once inside the body, the spike protein is produced, causing the immune system to recognise it and initiate an immune response. This means that if the body later encounters the spike protein of the coronavirus, the immune system will recognise it and destroy it before causing infection.

This Oxford-AstraZeneca vaccine uses the ChAdOx1 technology, which has been developed and optimised by the Jenner Institute over the last 10 years. This type of vaccine technology has been tested for many other diseases such as influenza (flu), meningococcus, plague and Middle East Respiratory Syndrome (MERS), another type of coronavirus.

The ChAdOx1 nCoV-19 vaccine was tested by the University of Oxford in clinical trials of over 23,000 people in the UK, Brazil and South Africa. A further trial with 40,000 people was also run by AstraZeneca in the USA, Argentina, Chile, Colombia and Peru. Trials were also conducted in India and Japan. 

Newer vaccines, such as mRNA vaccines and viral vector vaccines, differ from many traditional vaccines in the way they activate the immune system. Most traditional vaccines inject the antigen (part of the disease that stimulates an immune response) directly into the body.

In contrast, these two newer approaches deliver the genetic instructions for the antigen to the body’s cells. The cells then manufacture the antigen, which goes on to stimulate the immune response.

Injecting genetic material has raised questions about the use of these vaccines, such as whether they modify the DNA of those receiving them. However, this is not possible because the code cannot be incorporated into the body’s DNA.

how proteins are made


Click here for an accessible text version of this infographic

Protein subunit vaccines – Novavax

Subunit vaccines have been in use for many years, for example against hepatitis B and pertussis (whooping cough). This COVID-19 vaccine contains particles of the spike protein from the virus, along with an adjuvant to help generate a stronger immune response.

Together, these help the body’s immune system to respond to the vaccine and the virus when it encounters it in future.


Page last updated Monday, April 15, 2024