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Safety and effectiveness

Is the AstraZeneca vaccine safe?

The Medicines and Healthcare products Regulatory Agency (MRHA) and World Health Organization have said people should continue taking the Oxford/AstraZeneca vaccine because its benefits in preventing COVID infection far outweigh any risks.

 The risk of a blood clot is very low and blood clots are very rare – the chance is around four in one million. Once identified, the symptoms can be treated. This condition can also occur naturally and clotting problems are a common complication of COVID infection.

Although this condition is extremely rare, there does appear to be a higher risk in people who’ve had the first dose of the AstraZeneca vaccine.

For the vast majority of people being offered the Oxford-AstraZeneca vaccine, the benefits outweigh the risks. It is much safer for your immune system to learn how to fight illnesses through vaccination than by catching the virus and treating it, or suffering from long covid.

If people under 30 choose not to have the AZ, they may have a longer wait for an alternative to be available.

Who can have the AZ vaccine?

The MHRA and the JCVI advises that all adults aged over 50, people aged over 18 with an underlying health condition, and healthy adults over the age of 30 (including health and social care workers) should still receive any of the available COVID-19 vaccines which includes the AZ.

The MHRA and the Joint Committee on Vaccination and Immunisation (JCVI) advises that all adults aged 18-29 can receive any of the available COVID-19 vaccines however, it is preferable for them to have a vaccine other than AZ.  If people under 30 choose to have another COVID-19 vaccine they may have to wait to be protected. If they go ahead with the AZ vaccination this should be after considering all the risks and benefits.

People aged over 30 will not get a choice of what vaccine to have. People can decide not to have a certain vaccine, but this doesn’t mean an alternative type of vaccine will be offered.  

The benefits of vaccination in protecting you against the serious consequences of COVID-19 outweigh any risk of this rare condition. You should also complete your course with the same vaccine you had for the first dose.

Anyone who has already had clotting events with low platelets will not be given AZ vaccine and will be offered an alternative when available.

Pregnant women, who are booked in for a first or second dose of AZ, should talk to their GP.

What to look out for

While headaches are very common for people vaccinated, the British Society for Haematology stressed that those linked to these severe and rare clots are unusually severe and persistent and progressively worsen over days. Most cases are reported within two weeks of someone having the jab.

 Although very serious side effects are rare, the symptoms which people need to look out for from 4 days to 4 weeks after vaccination are:

  • A new, severe headache which is not helped by usual painkillers or is getting worse
  • A headache which seems worse when lying down or bending over
  • An unusual headache that may be accompanied by:
    • Blurred vision, nausea and vomiting
    • Difficulty with your speech
    • Weakness, drowsiness or seizures
  • New, unexplained pinprick bruising or bleeding
  • Shortness of breath, chest pain, leg swelling or persistent abdominal pain

If you have these symptoms and have had the AstraZeneca vaccine within the last two weeks, call 999. Once identified, the symptoms can be treated. 


How safe are the COVID vaccines?

The vaccines approved for use in the UK have met strict standards of safety, quality and effectiveness set out by the independent Medicines and Healthcare products Regulatory Agency (MHRA).

Any coronavirus vaccine that is approved must go through all the clinical trials and safety checks all other licensed medicines go through. The MHRA follows international standards of safety.

Other vaccines are being developed. They will only be available on the NHS once they have been thoroughly tested to make sure they are safe and effective.

So far, millions of people have been given a COVID-19 vaccine and reports of serious side effects, such as allergic reactions, have been very rare. No long-term complications have been reported.

To find out more about the vaccines approved in the UK, see:


How effective are the vaccines?  How long do they take to work?  

The MHRA have said these vaccines are highly effective, but to get full protection people need to come back for the second dose – this is really important.  

To ensure as many people are vaccinated as quickly as possible, the Department for Health and Social Care now advise that the second dose of both the OxfordAstraZeneca and the Pfizer/BioNtech vaccine should be scheduled up to 12 weeks apart.

Full protection kicks in around a week or two after that second dose, which is why it’s also important that when you do get invited, you act on that and get yourself booked in as soon as possible. Even those who have received a vaccine still need to follow social distancing and other guidance. 

Do the COVID-19 vaccines have side effects?

Like all medicines, vaccines can cause side effects. Most of these are mild and short-term, and not everyone gets them. Even if you do have symptoms after the first dose, you still need to have the second dose. You may not be protected until at least seven days after your second dose of the vaccine.

Very common side effects include:

  • Having a painful, heavy feeling and tenderness in the arm where you had your injection. This tends to be worst around 1–2 days after the vaccine
  • Feeling tired
  • Headache
  • General aches or mild flu like symptoms

As with all vaccines, appropriate treatment and care will be available in case of a rare anaphylactic event following administration.

How does the vaccine work? 

The vaccine works by making a protein from the virus that is important for creating protection.  

 The protein works in the same way they do for other vaccines by stimulating the immune system to make antibodies and cells to fight the infection. 

Can I give COVID-19 to anyone, after I have had the vaccine?  

The vaccine cannot give you COVID-19 infection, and two doses will reduce your chance of becoming seriously ill. We do not yet know whether it will stop you from catching and passing on the virus. So, it is important to follow the guidance in your local area to protect those around you.  

To protect yourself and your family, friends and colleagues you still need to:  

  • Practise social distancing 
  • Wear a face mask  
  • Wash your hands carefully and frequently  
  • Follow the current guidance www.gov.uk/coronavirus  

After I have had the vaccine will I still need to follow all the infection control advice?  

The vaccine cannot give you COVID-19 infection, and two doses will reduce your chance of becoming seriously ill. No vaccine is completely effective and it will take a few weeks for your body to build up protection. So, you will still need to follow the guidance in your workplace, including wearing the correct personal protection equipment and taking part in any screening programmes.  

To protect yourself and your family, friends and colleagues you still need to:  

  • Practise social distancing 
  • Wear a face mask  
  • Wash your hands carefully and frequently  
  • Follow the current guidance www.gov.uk/coronavirus  

Can the COVID-19 vaccines affect fertility?

No. There is absolutely no evidence, and no theoretical reason, that any of the vaccines can affect the fertility of women or men.

The British Fertility Society and Association of Reproductive and Clinical Scientists have created this document in response to questions that patients have been asking about Covid-19 vaccines and fertility. Click here for more information. 

The Royal College of Obstetricians & Gynaecologists and the Royal College of Midwives issued a press release responding to misinformation around COVID-19 vaccine and fertility. Royal College of Obstetricians and Gynaecologists have also published information and advice for pregnant women about the COVID-19 vaccine

I'm currently unwell with COVID should I get the vaccine?

People currently unwell and experiencing COVID-19 symptoms should not receive the COVID-19 vaccine until they have recovered.

Should people who have already had COVID get vaccinated or are suffering from Long COVID get vaccinated?

Yes, they should get vaccinated. There is no evidence of any safety concerns from vaccinating individuals with a past history of COVID-19 infection, or with detectable COVID-19 antibody, so people who have had COVID-19 disease (whether confirmed or suspected) can still receive the COVID-19 vaccine when it is their time to do so.

Do I need to leave a space between having the flu vaccine and having the COVID vaccine?  

It is not essential to leave time between the flu and COVID vaccine but it is recommended that there should be a gap of a week. We would always encourage anyone who is eligible but not yet taken up their flu jab to do so as soon as possible. 


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