Covid booster vaccines: what you need to know
Get the latest Covid-19 booster updates, from what the side effects are, to how long boosters take to be effective.
Updated 2 October 2023
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Covid-19 booster side effects
Top questions
Who is being offered a Covid-19 booster?
The vaccine is the best way to protect yourself against serious illness and hospitalisation from Covid-19. This is why people at higher risk, such as older people and those in clinical risk groups, are being offered another booster dose this autumn. The following groups are eligible:
- residents in a care home for older adults
- all adults aged 65 years and over
- people aged 6 months to 64 years in a clinical risk group, such as people who are pregnant or immunosuppressed (a full list is laid out in the Covid-19 Immunisation Green Book)
- frontline health and social care workers
- people aged 12 to 64 years who are household contacts of someone who is immunosuppressed (as detailed in the Green Book)
- people aged 16 to 64 years who are carers or staff working in care homes for older adults (as detailed in the Green Book).
If you are in one of these groups, you can book your booster by visiting the NHS website, using the NHS App or calling 119. You may also be offered a vaccination by GP surgeries or other local NHS services.
The Covid-19 virus is constantly changing. This means that even if you have had the vaccine before, your level of immunity is likely to be weaker than it was last year. Because of this, the NHS is encouraging those eligible to top up their protection as soon as possible ahead of the winter months.
How long does the booster last, and how effective is it?
Research published in the Lancet in July 2023 looked at how effective a third dose of the monovalent vaccine is at preventing hospitalisation from Covid-19. In people aged 65 or over, the vaccine was 50% effective at preventing serious illness, for up to six months after a third dose. More than a year (14 months) after vaccination, the effectiveness was still about the same level. In people aged 18 to 64 years, the vaccine was 30% effective after six months.
The research also looked at the effectiveness of the autumn 2022 bivalent booster. Having this booster meant that two to four weeks later, people aged 50 years and older had an extra 53% protection compared to those who didn't have it.
Additionally, a study published in The Lancet in April 2023 found that people over 65 who had the bivalent booster were 72% less likely to need a hospital visit and 68% less likely to die from Covid-19, compared to people over 65 who did not receive a bivalent booster.
How long does it take for the booster to be effective?
Studies have shown very high protection begins one or two weeks after receiving the booster jab.
A trial by Pfizer suggests that from seven days onwards, a booster dose of Pfizer is extremely effective at preventing illness from Covid-19.
I am immunosuppressed or immunocompromised, can I have a booster?
The Joint Committee on Vaccination and Immunisation (JCVI) has recommended that everyone over 6 months with a weakened immune system has an autumn booster.
This includes people whose immune systems do not work properly due to disease or treatment. For example, organ transplant recipients, those taking steroids, or cancer patients who are having chemotherapy. See Table 3 of the Covid-19 Immunisation Green Book for a full list.
What is a dual vaccine, or Omicron booster?
Updated versions of the Pfizer and Moderna vaccines have been approved for use in the UK.
These updated vaccines are 'bivalent' vaccines, which means they offer protection against both the original coronavirus, as well as the Omicron variants BA.4 and BA.5. You might also see them referred to as a ‘dual vaccine’, ‘dual variant vaccine’ or ‘Omicron booster’.
The Joint Committee on Vaccination and Immunisation (JCVI)’s guidance is that getting any Covid jab is more important than receiving a particular vaccine.
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Booster side effects
What are the side effects of the booster, and how long do they last?
Side effects of the booster are likely to be mild and short-lived. They often include things like pain or tenderness where you had the injection, fatigue, and headache.
- For more information about the side effects of Covid-19 vaccines, please visit the NHS website.
What are the side effects of the Moderna booster?
Side effects for the Moderna vaccine when used as a booster include pain or tenderness where you had the injection, swelling of the lymph nodes in the arm where you had the injection, tiredness, headache, muscle or joint pain, chills, nausea, vomiting, fever, or rash.
These side effects are similar whether you have the Moderna bivalent vaccine (also known as Omicron booster) or the original Moderna vaccine.
If you do experience side effects, these are likely to be mild and last no more than a few days.
What are the side effects of the Pfizer booster?
Symptoms for the Pfizer booster may include pain at the injection site, fatigue, headache, muscle and joint pain, fever and chills. The side effects may be milder after a booster than after previous doses.
Research from the UK COV-Boost trial suggests that Pfizer as a booster could have fewer side effects than Moderna, although there were some differences between different groups (see what are the side effects of the Moderna booster?)
Is myocarditis more common after the booster vaccine?
Myocarditis and pericarditis are very rare side effects of the Pfizer and Moderna vaccines.
Data published by the UK Health Security Agency (UKHSA) shows that myocarditis and pericarditis are less common after a booster jab, than after the first two doses of the vaccine, and this risk is already very small.
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