Adverse events and side effects

On this page you can find information about:

  • reported side effects and conditions following COVID-19 vaccination
  • links to relevant guidance and releases about specific reports

Myocarditis and pericarditis

There has been an increase in cases of myocarditis and pericarditis following vaccination with both Pfizer/BioNTech and Moderna vaccines.

Guidance on myocarditis and pericarditis after COVID-19 vaccination for healthcare professionals is now available.

View the information for healthcare professionals about COVID-19 vaccinations and these conditions on GOV.UK (external website).

Guillain-Barre Syndrome

The MHRA are analysing reports of Guillain-Barre Syndrome (GBS) following a COVID-19 vaccination.

A link between GBS and COVID-19 vaccination has not been proven.

For more information, view guidance about GBS and COVID-19 vaccination on GOV.UK. 

Menstrual disorders and unexpected vaginal bleeding

The MHRA has reviewed reports of menstrual disorders and unexpected vaginal bleeding suspected as adverse reactions to vaccination with the three COVID-19 vaccines currently being used in the UK:

  • Pfizer/BioNTech
  • COVID-19 Vaccine AstraZeneca
  • COVID-19 Vaccine Moderna

These reports have also been reviewed by:

  • independent experts of the Commission on Human Medicines’ COVID-19 Vaccines Benefit Risk Expert Working Group
  • members of its Medicines for Women’s Health Expert Advisory Group

As with any suspected side effects from the COVID-19 vaccines, including those in relation to menstrual disorders, please continue to report via the Yellow Card scheme (external website).

The MHRA’s rigorous evaluation of reports of suspected side effects of period problems does not support a link between changes to people’s periods and related symptoms and COVID-19 vaccines.

There is no evidence to suggest that COVID-19 vaccines will affect fertility and your ability to have children.

Our advice remains that the benefits of vaccination outweigh the risks for most people.

It is important that people come forward for their first and second vaccine doses when invited.

While uncomfortable or distressing, period problems are extremely common.

Stressful life events can disrupt your periods.

Changes to the menstrual cycle have also been reported following infection with COVID-19 and in women affected by long-COVID.

Following COVID-19 vaccination, please contact your doctor if you have:

  • changes to your periods that are unusual for you or persist over time
  • any new vaginal bleeding after the menopause


Last updated: 02 March 2022