Covid-19: everything you need to know
Covid-19 frequently asked questions
Last updated: 29 May 2025
Millions of people have had a Covid-19 vaccine since the pandemic started. It's thought that the vaccines have saved countless lives around the world.
The majority of people in the UK have now had their first two jabs, and eligible people are receiving boosters.
On this page you’ll find answers to frequently asked questions about the Covid vaccine, and links to further information from trusted, reliable resources.
General information
What are the Covid-19 vaccines?
What's in the Covid-19 vaccines? (vaccine ingredients)
I’m allergic to a number of medications, including penicillin, can I still have the vaccine?
Which Covid-19 vaccine is best?
How effective is the Covid-19 vaccine?
Can you spread Covid-19 after getting the vaccine?
Can I get the Covid-19 vaccine if I have a cold?
Is the vaccine permitted in my religious community?
Can I drink alcohol after having the Covid-19 vaccine?
Do I need a vaccine, if I've already had Covid-19?
Can I get Covid-19 again after 90 days of testing positive?
Are the Covid-19 vaccines safe?
How soon after getting the Covid-19 vaccine are you protected?
Symptoms
How long does it take for Covid-19 symptoms to appear?
How long do Covid-19 symptoms last?
Side effects
What are the Covid-19 vaccine side effects?
Does the Covid-19 vaccine affect menstrual cycles?
Pregnancy and fertility
Does the Covid-19 vaccine affect fertility?
Can you have the Covid-19 vaccine if you're pregnant or breastfeeding?
Children
Can children get the Covid-19 vaccines?
Boosters
Do I need a Covid-19 booster vaccine?
Who is eligible for a Covid-19 booster vaccine?
When will I be offered a Covid-19 booster vaccine?
Which Covid-19 vaccine will I receive for the booster dose?
How do I book a Covid-19 booster vaccine?
Is it safe to have the flu and Covid-19 booster vaccine at the same time?
What are Covid-19 variants?
All viruses change over time. Most changes have little to no impact on the virus’ properties. However, some changes may affect the virus’ properties, such as how easily it spreads, the associated disease severity, the performance of vaccines, therapeutic medicines, diagnostic tools or other public health and social measures.
In 2022, Omicron was the world's most dominant variant. While the variant spread faster and to more people, it generally causes milder illness in vaccinated people. Around April 2024, a new FLiRT variant was reported in the UK.
Do I need a Covid-19 booster vaccine?
Protection from the Covid vaccines doesn’t last forever in your body. Like many other vaccines, the Covid vaccines will reduce over time.
Booster vaccines are being offered to eligible individuals to help extend protection against Covid.
Several studies into the Covid vaccines suggest that while protection against severe disease remains high in most groups at least 5-6 months after the second dose of a Covid vaccine, there is evidence that protection against infection and symptomatic disease will decrease.
Who is eligible for a Covid-19 booster vaccine?
Covid boosters are currently being offered to eligible groups who have a higher risk. If you are eligible, you will be offered a booster dose at the next seasonal Covid vaccine campaign.
Like some other vaccines, levels of protection may begin to reduce over time. This booster dose will help extend the protection you gained from your first 2 doses.
It will also give you longer term protection and reduce the risk of you needing admission to hospital due to Covid infection this winter.
When will I be offered a Covid-19 booster vaccine?
The Covid booster vaccine will be available to eligible groups during a seasonal vaccination campaign. The NHS will contact you when the seasonal vaccine campaign reopens and you are eligible.
Which Covid-19 vaccine will I receive for the booster dose?
If eligible, you will be given a booster dose of either Pfizer or Moderna vaccine. These vaccines have already been given to millions of people in the UK.
You will not get to choose but you will be offered the right vaccine for you. It may be the same or different from the vaccines that you had before.
How do I book a Covid-19 booster vaccine?
Once you’ve been contacted to say you are eligible for a Covid vaccine, there are several ways you can get an appointment:
- Visit a walk-in vaccination centre.
- Through your local GP or NHS service
- Through your care home
- Wait to be contacted by your local GP, or NHS service, and book directly with them.
If you have been offered a booster vaccination because you are considered high risk, when visiting a walk-in centre, please bring your booster invitation letter, or a letter from your doctor explaining your health condition.
If you are a frontline health or social worker, you’ll need to bring proof of your employment to your walk-in booster appointment, such as your workplace photo ID.
You must wait 8-12 weeks between the date of your second dose before going for your booster vaccine.
How long do I have to wait before I can book a Covid-19 booster vaccine after testing positive for Covid-19?
If you have tested positive for Covid and are eligible for a Covid booster vaccine, you’ll need to wait until you have recovered and feel well enough before you can get the Covid booster vaccine.
Is it safe to have the flu and Covid-19 booster vaccine at the same time?
Yes. If you are offered both the flu and Covid booster vaccines, it is safe to have them at the same time, according to the NHS.
How do the Covid-19 vaccines work?
The Covid vaccines work in the same way all vaccines do: by sending a signal to our immune system to create the antibodies that will fight the virus. Once your immune system knows how to fight disease, it can protect you in the event of exposure.
Getting a vaccine is a much faster and safer way for your immune system to learn how to create the antibodies required to protect you from a disease, rather than catching the disease or virus itself.
If enough people are vaccinated, it’s harder for the virus to spread to people who are unable to have vaccines. For example, people who are ill or have a weakened immune system. This is called ‘herd immunity’.
Find out more about the history of vaccines
What are the Covid-19 vaccines?
The two vaccines used in the UK are:
- The Pfizer/BioNTech vaccine, also known as the Pfizer vaccine, BioNTech vaccine or by its trade name 'Comirnaty', which was rolled out in January 2021.
- The Spikevax vaccine, previosuly known as Moderna, became available in April 2021.
The AstraZeneca vaccine is no longer used in the UK. Evidence shows that mRNA vaccines, Pfizer and Moderna, are more effective at boosting protection from Covid, so these vaccines are being recommended for primary courses and booster programme.
The Novavax vaccine has also been approved for people who can’t have mRNA-based vaccines due to allergies.
What's in the Covid-19 vaccines? (vaccine ingredients)
The ingredients in the Covid vaccines are very similar to the ingredients found in childhood vaccines, with many commonly found naturally in the human body, such as salt and water. The active vaccine ingredients make up a few thousandths of a gram - this is what actively prepares the body to fight the virus.
The Covid vaccines do not contain chimpanzee cells, foetal tissues, animal products or eggs, and are suitable for vegans and vegetarians.
What's in the Pfizer/BioNTech vaccine?
The Pfizer vaccine is an mRNA vaccine (messenger RNA), delivered in two doses (0.3 ml each). The active ingredient (highly purified single-stranded, 5’-capped messenger RNA ) sends instructions to the body’s cells to make specific viral proteins that can be recognised by the immune system to fight the Covid virus.
The DNA sequence known as the SV40 promoter is present in the Pfizer-BioNTech vaccine. The SV40 promoter is a synthetic DNA sequence commonly used in molecular biology to help express genes in laboratory settings. It is not the SV40 virus and it is not derived from animals.
The presence of this sequence is a residual fragment from the vaccine manufacturing process and is non-functional. Regulatory authorities, including the UK Medicines and Healthcare products Regulatory Agency (MHRA), have confirmed that the amount of residual DNA is well within safe limits and poses no safety concerns.
What's in the Moderna vaccine?
The Moderna vaccine works in exactly the same way as the Pfizer vaccine. It's an mRNA vaccine, delivered in two doses (0.5ml each).
I’m allergic to a number of medications, including penicillin, can I still have the vaccine?
None of the Covid vaccines contain penicillin.
Both the Pfizer/BioNTech and Moderna vaccines contain a compound called Polyethylene glycol (PEG) – used to stabilise the lipid particles in the vaccine, and the Oxford/AstraZeneca vaccine contains Polysorbate-80 (an emulsifier which helps to stabilise the vaccine).
Both of these compounds are closely related, and are found in many other medications.
If you have a known severe allergy or anaphylactic reaction to either of these compounds, or have had an unexplained severe reaction in the past you should discuss vaccination with your GP or health professional.
What are the Covid-19 vaccine side effects?
The most common Covid vaccine side effects include:
- a sore arm where the needle went in
- tenderness or aching in the arm
- tiredness, headaches, general aches and mild flu like symptoms, for some.
Side effect symptoms are generally mild and will usually last one to two days. Some people can experience them for longer - up to one week.
Everyone is different, so the side effects you might experience (if you get any at all) will depend on which vaccine you receive, whether it’s the first or second dose, and you as an individual.
All Covid vaccines approved for use in the UK with authorisation from the Medicines and Healthcare products Regulatory Agency (MHRA) are considered safe, and will continue to be monitored for safety and effectiveness.
When to seek urgent medical advice
If you are worried about your symptoms or if they are getting worse, contact NHS 111 and let them know about your vaccination.
Reports of risk of heart inflammation with Pfizer and Moderna vaccines
There have been extremely rare reports of inflammation of the heart reported after Covid vaccination with Moderna and Pfizer/BioNTech vaccines. Most people who had this recovered following rest and simple treatments.
The MHRA is continuing to investigate both the occurrences and any risk factors. They have occurred most frequently in younger males shortly after the second dose of the vaccine.
Anyone who has any of these symptoms within a few days of being vaccinated should seek urgent medical advice:
- chest pain
- shortness of breath
- a fast beating, fluttering or pounding heart (palpitations)
Check for regular updates on Covid vaccine side effects
What should you do if you're experiencing Covid-19 vaccine side effects?
Mild Covid vaccine side effects are common but not everyone will get them. Side effects usually last one to three days, but can last up to one week.
If you do experience symptoms, it’s still important to have your second dose. The second dose of the vaccine will give you the best protection against the virus.
If you are experiencing side effects:
- Rest until you feel better.
- Take the normal dose of paracetamol (follow the advice on the packaging) to help ease mild symptoms.
- If your symptoms seem to get worse or if you are concerned, call NHS 111.
- If you do seek advice from a doctor or nurse, let them know you’ve been vaccinated and show them your vaccination card so that they can assess you properly.
You can also report suspected side effects of vaccines and medicines online through the Yellow Card scheme.
Does the Covid-19 vaccine affect menstrual cycles?
An evaluation into reports of menstrual disorders following the Covid vaccines found that the number of reports of menstrual disorders and vaginal bleeding were low in relation to both the number of people who have received Covid vaccines to date, and therefore did not support a link between changes to menstrual periods, related symptoms and Covid vaccines.
The MHRA continues to closely review reports of suspected side effects of menstrual disorders and unexpected vaginal bleeding, and anyone experiencing unusual changes to their periods following Covid vaccination, should contact their doctor.
Does the Covid-19 vaccine affect fertility?
There is no evidence that the Covid vaccines have any effect on male or female fertility, and there is no need to avoid pregnancy after vaccination.
Can you have the Covid-19 vaccine if you're pregnant or breastfeeding?
If you're pregnant, it's important to get vaccinated as soon as you are offered one. There is growing evidence showing that women who are pregnant are at increased risk of serious consequences from Covid-19.
It is currently recommended for you to have the Pfizer/BioNTech or Moderna vaccine if you’re pregnant (because they've been more widely used during pregnancy in other countries).
If you are worried about being vaccinated whilst pregnant or breastfeeding, speak to your healthcare professional (GP or midwife) before you have the vaccination. They will discuss the benefits and risks with you.
The vaccine cannot give you or your baby Covid. You can also have the Covid vaccine if you're breastfeeding.
Can children get the Covid-19 vaccines?
Yes the vaccine is available to children from 6 months old if they are have a weakened immune system. Parents and guardians will get a letter with information about when the vaccine will be offered.
Are the Covid-19 vaccines safe?
Yes, the vaccines are safe and effective, and will give you the best protection against Covid. While they were developed far quicker than the average 8-10 years required for previous vaccines, this is because of the massive effort by researchers, the money invested by governments, and the willingness of volunteers to trial them.
All vaccines approved were rigorously tested before being approved, and have met the strict standards of safety, quality and effectiveness set out by the MHRA.
Vaccines are the most effective way to prevent infectious diseases and save up to 3 million lives worldwide every year. Thanks to vaccine roll-outs in the past, diseases like smallpox, polio and tetanus no longer exist or are very rare.
How effective is the Covid-19 vaccine?
The Pfizer and Moderna vaccines have been updated to better target recent variants. They’re given alongside the original vaccines. These updated ‘bivalent’ or ‘combined’ vaccines include a half dose of the original vaccine, and a half-dose of an updated formula, which is designed to better target the Omicron variant.
Both the original and updated vaccines are shown to offer a good boost in protection - between 70 – 90% - so whichever vaccine you are offered will help to top-up your protection.
How soon after getting the Covid-19 vaccine are you protected?
You are partially protected from Covid three to four weeks after receiving your first Covid vaccine. But it’s important to receive 2 doses for stronger and longer-lasting protection.
Learn more about Covid vaccine protection on the NHS website.
Can I get Covid-19 again after 90 days of testing positive?
Yes, you can. If you test positive for Covid again, 90 days after testing positive using a PCR or rapid lateral flow test, it should be considered a new infection.
The 90-day period is from the initial onset of symptoms or from confirmation of a positive test result, if asymptomatic.
Sources
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