AstraZeneca vaccine: side effects of first and second dose - and blood clot and stroke risk explained

UK health officials are seeking to maintain public confidence in the AstraZeneca Covid-19 vaccine due to its potential link to blood clots.

People under the age of 40 are now being offered the Pfizer or Moderna vaccine, while anyone who received a first dose of the AstraZeneca vaccine will continue to be offered a second dose of the same vaccine, irrespective of their age.

The decision to stop administering the AstraZeneca vaccine to people under 40 earlier this year came after the MHRA said the balance of risk for the jab is very favourable for older people, but is “more finely balanced” among younger age groups, who do not tend to suffer serious illness from coronavirus.

Separately, a review by the European Medicines Agency (EMA) concluded that “unusual blood clots with low blood platelets should be listed as very rare side effects” of the AstraZeneca vaccine.

Scientists believe they may have identified the “trigger” behind the extremely rare blood clot complications from the jab.

An international team of researchers in Cardiff and the US said the reaction can be traced to the way a component of the vaccine binds with a specific protein in the blood. This may then cause a chain reaction in the immune system which can lead to the development of blood clots - a condition known as vaccine-induced immune thrombotic thrombocytopenia (VITT).

Professor Alan Parker, from Cardiff University’s School of Medicine, said: “VITT only happens in extremely rare cases because a chain of complex events needs to take place to trigger this ultra-rare side effect.

“Our data confirms PF4 can bind to adenoviruses, an important step in unravelling the mechanism underlying VITT. Establishing a mechanism could help to prevent and treat this disorder.

“We hope our findings can be used to better understand the rare side effects of these new vaccines – and potentially to design new and improved vaccines to turn the tide on this global pandemic.”

The risk of developing a blood clot after the AstraZeneca vaccine is extremely rare and has only occured in a very small number of cases.

However, some other more common side effects can be expected after the jab, but these should start to clear after around five days.

What are the side effects of the AstraZeneca vaccine?

Some people may experience side effects after receiving the AstraZeneca Covid-19 vaccine.

In clinical studies, most of the side effects were mild to moderate in nature and resolved within a few days, with some still present a week after vaccination. However, side effects do not occur in every case with some people experiencing no symptoms at all.

If you do experience any side effects, these will typically only last for a few days.

The following symptoms are the most common after receiving the coronavirus vaccine, and affect more than one in 10 people. These may include:

- tenderness, pain, warmth, itching or bruising where the injection is given

- generally feeling unwell

- feeling tired (fatigue)

- chills or feeling feverish

- headache

- feeling sick (nausea)

- joint pain or muscle ache

Other common symptoms, which can affect up to one in 10 people, include:

- swelling, redness or a lump at the injection site

- fever

- being sick (vomiting) or diarrhoea

- flu-like symptoms, such as high temperature, sore throat, runny nose, cough and chills

In some cases, people may experience side effects such as swollen glands or dizziness, but these symptoms are much less common and may only affect up to one in 100 people. These include:

- feeling dizzy

- decreased appetite

- abdominal pain

- enlarged lymph nodes

- excessive sweating, itchy skin or rash

In light of the possible link to blood clots, the MHRA is now advising as a precautionary measure that anyone who experiences any of the following symptoms four days or more after vaccination should seek medical advice:

- a new onset of severe or persistent headache, blurred vision, confusion or seizures

- develop shortness of breath, chest pain, leg swelling or persistent abdominal pain,

- unusual skin bruising or pinpoint round spots beyond the injection site

What if I get a fever?

Some people have reported a sudden feeling of cold with shivering and shaking accompanied by a rise in temperature, possibly with sweating, headache, nausea, muscle aches and feeling unwell, starting within a day of having the vaccine and usually lasting for a day or two.

If your fever is high and lasts longer than two or three days, or you have other persistent symptoms, this might not be due to side effects of the vaccine and you should follow appropriate advice according to your symptoms.

Will I get side effects with the second dose?

Side effects after your second dose are likely to be more intense than the ones experienced after the first. This is completely normal and is a sign that your body is building protection against the virus.

It is important to get two doses of the vaccine, even if you have mild side effects after the first dose. In both cases, symptoms should only last for a few days.

Can I take anything for the symptoms?

You can take painkillers, such as paracetamol and ibuprofen, to help ease any post-vaccination side effects you might have.

It is not recommended that you take these medicines before your vaccination for the purpose of trying to prevent side effects.

To reduce pain and discomfort from the site of the injection, you should apply a clean, cool, wet washcloth over the area, and use or exercise your arm.

To help minimise discomfort from fever, make sure to drink plenty of fluids.

When should I see a doctor?

If you notice any side effects not mentioned in the leaflet provided following your vaccination, you should inform your doctor, pharmacist or nurse.

If you are worried about any symptoms you experience, you can phone the NHS 24’s 111 service for help.

Dr June Raine, MHRA chief executive, said: “The public’s safety is always at the forefront of our minds and we take every report of a suspected side effect very seriously indeed.

"We thoroughly analyse each and every report as we receive it and although the number of reports of CVST and other thromboembolic events has increased over the last week, so has the overall number of vaccinations administered, therefore these blood clots remain extremely rare and unlikely to occur.

“We ask anyone who suspects they have experienced a side effect linked with their Covid-19 vaccine to report it to the Coronavirus Yellow Card website.

“It is still vitally important that people come forward for their vaccination when invited to do so.”

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