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Covid-19 Primary Care Resources

Adverse effects of Covid vaccines

flu vaccine

The most frequently reported adverse effects to the different vaccines and when to report an adverse effect

This information is sourced from the Specialist Pharmacy Service, data on Vaccinations, Yellow card reporting link, ‘What to expect’,, AZ, Moderna, Yellow card reporting summary and the UKHSA:

The MHRA are collecting data, via the yellow card scheme on what side effects have been observed from the UK vaccine programme.

Information for patients

Very common side effects from all vaccines in the first day or two include:

  • having a painful, heavy feeling and tenderness in the arm where you had your injection
  • feeling tired
  • headache, aches and chills
  • flu like symptoms.

However, a high temperature could also indicate that you have Covid-19 or another infection. You can rest and take the normal dose of paracetamol.

Uncommon side effects include:

Swollen glands in the armpit or neck on the same side as the arm where you had the vaccine. This can last for around 10 days, but if it lasts longer see your doctor. If you are due for a mammogram in the few weeks after the vaccine, then you should mention that when you attend.

Rare and significant side effects particularly related to AstraZeneca and Janssen vaccine:

  • A new, severe headache which is not helped by usual painkillers or is getting worse
  • An unusual headache which seems worse when lying down or bending over or 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.

Rare and significant side effects particularly related to Pfizer and Moderna vaccines:

Rare cases of inflammation of the heart called myocarditis or pericarditis have been reported after Pfizer and Moderna Covid-19 vaccines.

These cases have been seen mostly in younger men within several days after vaccination.

Most of these people recovered and felt better following rest and simple treatments.

You should seek medical advice urgently if you experience:

  • chest pain
  • shortness of breath
  • feelings of having a fast-beating, fluttering, or pounding heart

Information for clinicians

Vaccine injury is rare. The chances of death or serious illness from Covid far outweigh the possible risks of Covid vaccination.

Side effects of all vaccine types:

  • Anxiety related reactions: syncope, dizziness, palpitations, increased heart rate, sweating at the time of vaccination are stress related and temporary. Try to put in place precautions to prevent injury from fainting.
  • Bruising/bleeding — especially if on anticoagulants/thrombocytopaenic.

Vaccine specific side effects:


  • Anaphylaxis has been reported in a small number of cases with Pfizer (and Moderna) Covid-19 vaccine
  • Recipients should usually be kept for observation for a minimum of 15 minutes. However, to help accelerate delivery of the programme in response to the emergence of the Omicron variant, the UK Chief Medical Officers have recommended a temporary suspension of this requirement, for individuals without a history of allergy.
  • Do not give further dose if anaphylaxis to first/booster
  • Myocarditis/pericarditis – very rare, usually within 10 days of vaccination, more common after second dose and in younger men.  Be alert to the signs and symptoms (acute, persisting chest pain/shortness of breath, tachycardia or palpitations, new onset unexplained dizziness or syncope)

AstraZeneca (AZ) and Janssen

(Both are recombinant DNA vaccines and share a very similar side effect profile.)

Thrombosis with thrombocytopenia and coagulation disorders

Thrombosis with thrombocytopenia syndrome (TTS), in some cases accompanied by bleeding, has been observed very rarely following vaccination with the AZ and Janssen vaccines. This includes severe cases presenting as venous thrombosis, including unusual sites such as cerebral venous sinus thrombosis, splanchnic vein thrombosis, as well as arterial thrombosis, concomitant with thrombocytopenia. Some cases had a fatal outcome.

For AZ, the majority of these cases occurred within the three weeks following vaccination but some have also been reported after this period. Risk factors have not been identified. Some cases had increased D-dimer levels >4000ng/ml, positive platelet factor 4 antibodies and/or laboratory evidence of platelet activation.

With the Janssen vaccine, cases occurred within the first three weeks following vaccination, and mostly in women under 60 years of age.

Vaccinated individuals should be instructed to seek immediate medical attention if four or more days after vaccination they develop:

  • new onset or worsening severe or persistent headaches with blurred vision, which do not respond to simple painkillers
  • new symptoms such as shortness of breath, chest pain, leg swelling, leg pain, persistent abdominal pain
  • any neurological symptoms or signs such as confusion or seizures
  • unusual skin bruising and/or petechiae beyond the site of vaccination.

Individuals diagnosed with thrombocytopenia within 3 weeks after vaccination with the AZ or Janssen vaccine should be actively investigated for signs of thrombosis. Individuals who present with thrombosis within three weeks of vaccination should be evaluated for thrombocytopenia.

Patients with TTS should be urgently referred secondary care.

Capillary leak syndrome (CLS)

Very rare cases CLS have been reported in the first days after vaccination with both vaccines.

CLS is a rare disorder characterised by acute episodes of oedema mainly affecting the limbs, hypotension, haemoconcentration and hypoalbuminaemia.

Patients with an acute episode of CLS following vaccination require prompt recognition and treatment.

Individuals with a known history of CLS should not be vaccinated with either AZ or Janssen vaccines.

Neurological events

Guillain-Barré Syndrome (GBS) has been reported very rarely following vaccination.


Myocarditis and pericarditis

There have been very rare reports of myocarditis and pericarditis occurring after vaccination with Moderna, often in younger men and shortly after the second dose of the vaccine. These are typically mild cases and individuals tend to recover within a short time following standard treatment and rest. Be alert to the signs and symptoms (acute, persisting chest pain/shortness of breath, tachycardia or palpitations, new onset unexplained dizziness or syncope within 10 days of vaccination)


As above, for Pfizer Covid-19 vaccine.

Hypothesised side effects of any vaccine

(These are under investigation but not proven.)

Bell’s Palsy

The MHRA continues to review reports of suspected Bell’s Palsy.

The number of reports of facial paralysis received so far is similar to the expected natural rate and does not currently suggest an increased risk following the vaccines.

Menstrual changes

The menstrual changes reported are mostly transient in nature.

There is no evidence to suggest that Covid vaccines will affect fertility Changes to the menstrual cycle have also been reported following infection with Covid-19 and in people affected by long-Covid

Facial swelling in those with a history of facial dermal fillers

Rare reports of facial swelling occurring 1-2 days after vaccination in vaccine recipients with a history of injection of facial fillers were observed in the clinical trials for the Moderna Vaccine.

The MHRA has also received Yellow Card reports of facial swelling in those with a history of injection of facial fillers for the Pfizer Vaccine. In most instances, the facial swelling was mild, transient and was localised to the site of the dermal filler.

Reporting side effects

Side effects are reported to the MHRA Yellow card scheme.

ALL suspected side effects should be reported, even minor effects.

Patients can self-report.

Adverse effects can be reported at any time following vaccine administration.

Side effects can be reported after first, second and third or booster doses.

It’s important to include:

  • Information on the person who has experienced the side effect (essential).
  • The name of the vaccine suspected to have caused the side effect (essential). Include the vaccine brand and batch/lot number if available.
  • A description of the side effect (essential).
  • Any other medicines being taken around the same time, including non-prescription and herbal remedies (if available, if not please do not let this prevent you submitting a report).
  • Any other health condition that the person who experienced the side effect may have (if this information is available)

Written by Dr Carrie St John Wright


Specialist Pharmacy Service: Reporting suspected Covid-19 vaccine side effects, and potential product defects or counterfeit products

Published: 24/01/2022


UK HSA: Myocarditis and pericarditis after COVID-19 vaccination: clinical management guidance for healthcare professionals

Published: 07/12/2021


MHRA Decision; Information for Healthcare Professionals on Covid-19 Vaccine AstraZeneca

Published: 19/07/2021


MHRA Decision; Information for Healthcare Professionals on Pfizer/BioNTech Covid-19 Vaccine

Published: 09/07/2021


UK Government. Patient Information Leaflet for COVID-19 Vaccine Janssen – GOV.UK (


MHRA Decision; Information for Healthcare Professionals on Covid-19 Vaccine Moderna

Published: 25/06/2021


UK Government. What to expect after your Covid-19 vaccination

Published: 09/11/2021


UK Government. Information for UK recipients on COVID-19 Vaccine AstraZeneca (Regulation 174) – GOV.UK (

Updated: 26/01/2022


UK Government. Patient Information Leaflet for COVID-19 Vaccine Janssen – GOV.UK (

Published: 03/11/2021


UK Government. Patient Information Leaflet for COVID-19 Vaccine Pfizer/BioNTech – GOV.UK (

Updated: 24/12/2021


UK Government. Patient Information Leaflet for Spikevax – GOV.UK (

Updated: 24/12/2021


EMC. Summary of medicinal product characteristics: Comirnaty

Published: 21/12/2020; last updated: 15/11/2021


UK Government. The Green Book. Chapter 14a – COVID-19 – SARS-CoV-2

Last updated: 11/01/2022


UK Government. Summary of product characteristics for Covid-19 vaccine Janssen

Updated: 03/11/2021


UK Government. Summary of product characteristics for Spikevax

Updated: 24/12/2021


UK Government. Coronavirus (COVID-19) vaccines adverse reactions

Published: 5/02/2021


MHRA Coronavirus Yellow Card reporting site