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Can families believe the accuracy of websites’ information regarding COVID-19 vaccines’ side effects?
  1. Luke Harvey-Nguyen1,
  2. David Tuthill2
  1. 1 Cardiff University School of Medicine, Cardiff, UK
  2. 2 Paediatrics, Children's Hospital for Wales, Cardiff, UK
  1. Correspondence to Luke Harvey-Nguyen, University Hospital of Wales, Cardiff CF14 4XN, UK; harvey-nguyenl{at}

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COVID-19 has a substantial mortality, particularly among the elderly. Vaccination substantially reduces this mortality for adults. Vaccines’ side effects include rare events such as thrombotic events and myocarditis. As children and young people are at a substantially lower risk of mortality/severe disease from COVID-19, the risk–benefit ratio for vaccination is less advantageous in this age group. On 4 August 2021, the Joint Committee on Vaccination and Immunisation advised that all teenagers 16–17 years old in the UK should be offered the Pfizer-BioNTech vaccine. Subsequently, on purely medical grounds, they did not recommend vaccinating children 12–16 years old routinely.1 After consultation on the wider benefits of maintaining schooling and aiding children’s mental health, the U.K.’s Chief Medical Officers have recommended (13 September 2021) that the Pfizer-BioNTech vaccine be offered to children aged 12–15. The RCPCH has cautiously endorsed this development as part of a wider package to maintain children’s schooling and health.2 Currently, the UK has four licensed COVID-19 vaccines (Oxford/AstraZeneca, Johnson & Johnson, Pfizer/BioNTech and Moderna).3 All have potential side effects. Thus, it is important that teenagers and their families are well informed about the balance between the benefits and genuine side effects of vaccination, while avoiding misinformation. Other than healthcare professionals and families/friends, the internet is the major source of such information.


To review the accuracy of purported COVID-19 vaccine side effects listed on websites.


Side effects of the COVID-19 vaccines listed in the BNF were combined with those in each of the four manufacturers’ patient information leaflets to create a comprehensive “Gold Standard” list of ‘correct’ side effects. These included myocarditis and thrombosis. For simplicity, we did not specify which vaccine had which specific side-effect profile, as websites do not differentiate individual vaccines. Online websites’ statements were then compared with this list for accuracy. The first 10 websites found on each of nine different search engines were evaluated.


From the 10 top hits found in each of 9 search engines, 44 unique websites from a possible 90 were identified. Of these, 33 sites (75%) documented only side effects found in the “Gold Standard” list of side effects collated for this study. A quarter (11/44) document at least one side effect that does not appear in the “Gold Standard” list. Ecosia, Dogpile and Bing were the most accurate engines, with only 10% in each having a website listing unrecognised side effects. documented the highest percentage of hits containing at least one unrecognised side effect—40% (table 1). A total incidence of 55 ‘extra’ side effects were recorded (table 2).

Table 1

Search engine and percentage incidence of hits including at least one ‘extra’ side effect when compared with the combined “Gold Standard” list

Table 2

Search engine and incidence of ‘extra’ side effects when compared with the combined “Gold Standard” list


The COVID-19 immunisation plan, and its recent extension to include older children, makes it important that families are provided with reliable, accessible information. Additional rare side effects may still be discovered in the future, but probably will not substantially affect family’s perceptions. Most easily accessible websites contain reasonably accurate information about COVID-19 vaccine side effects. However, some contain unsubstantiated side effects which could adversely affect the decision of those trying to make informed vaccination choices.

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Patient consent for publication

Ethics approval

This study does not involve human participants.



  • Contributors Project idea conceived by DT, performed by LH-N; paper and analysis performed by both.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests DT has a longstanding interest in medication safety and chairs the Paediatric Formulary Committee of the BNFc.

  • Provenance and peer review Not commissioned; externally peer reviewed.