What are the safety concerns and what are the serious side effects reported with existing SARS-CoV-2 vaccines?

Originally published 25 Apr 2021, updated 3 Aug 2021
Respiratory conditions
  • COVID-19
Type of resource
IPCRG COVID-19 and respiratory Q&A

What the research says:

Clinical trial results support the safety of currently available SARS-CoV-2 vaccines (Yuan et al 2021). The most commonly reported side effects in clinical trials were injection site pain, fatigue, headache, fever and chills. Serious adverse events were rare and the number and nature of such events was similar between vaccine and placebo groups.


Extensive real-world data safety surveillance is underway. Rare cases of Vaccine Induced Thrombocytopenic Thrombosis (VITT; also described as thrombosis with thrombocytopenia syndrome [TTS]) have been reported following administration of the Oxford-AstraZeneca (EMA 2021) and the Johnson & Johnson/Janssen viral vector vaccines (CDC July 13, 2021). VITT are thrombotic events in the context of thrombocytopenia (including clots in the vessels draining blood from the brain [CVST] and disseminated intravascular coagulation[DIC]) (Greinacher et al 2021). For the Oxford-AstraZeneca SARS-CoV-2 vaccine VITT have been reported at a rate of around 25 events per 20 million vaccinations (EMA 2021). For both vaccines, the majority of such events have been reported among women <50 years of age. Severe cases of anaphylaxis have been reported following administration of the Pfizer RNA-based SARS-CoV-2 vaccine at a rate of ~5 cases per 1 million vaccinations as of February 2021 (Remmel 2021). Severe cases of anaphylaxis have also been reported following administration of the Moderna RNA-based SARS-CoV-2 vaccine. In the USA 10 cases per ~4 million vaccinations had been reported as of January 10 2021 (CDC January 29, 2021). Such events usually occur within ~15 minutes of vaccine administration. These safety concerns appear to arise mainly following the first dose of vaccine.


Rare cases of myocarditis have been reported following administration of the Pfizer and Moderna RNA-based SARS-CoV-2 vaccines, notably among male adolescents and young adults, more often after the second dose and typically emerging within a few days of vaccination (CDC June 23, 2021).


Risk-benefit analysis remains in favour of vaccination: World Health Organization (WHO) statement “At this time, WHO considers that the benefits of the AstraZeneca vaccine outweigh its risks and recommends that vaccinations continue”. The WHO provide a reporting route for any adverse events (WHO Team 2021).

What this means for your clinical practice:

  •  Continue to vaccinate using available, approved vaccines according to National guidance.
  • The WHO recommend monitoring patients for 15 mins after vaccination and for 30 mins for those with previous reaction to vaccination (WHO Team 2021).
  • Monitor for and report any adverse events in the usual way (WHO Team 2021).