Safety of the messenger RNA Pfizer vaccine was evaluated by Barda and others and published in the New England Journal of Medicine on August 25th. 

Background trials showed that messenger RNA based vaccines against severe acute respiratory syndrome coronavirus, SARS-CoV-2, have a good safety profile, yet these trials were subject to size and patient-mix limitations.  

An evaluation of the Pfizer vaccine with respect to a broad range of potential adverse events was needed.  

This study used data from the largest healthcare organisation in Israel to evaluate the safety of the BNT162b2 mRNA vaccine Pfizer.  For each potential adverse event, in a population of persons with no previous diagnosis of that event, they individually matched vaccinated persons to unvaccinated persons according to sociodemographic and clinical variables.  

Risk ratios and risk differences at 42 days after vaccination were derived using the Kaplan–Meier estimator.  To place these results in context, they performed a similar analysis involving SARS-CoV-2–infected persons matched to uninfected persons.  The same adverse events were studied in the vaccinated and SARS-CoV-2 infection analyses.  

Their results showed that in the vaccination analysis, the vaccinated and control groups each included a mean of 884,828 persons.  Vaccination was most strongly associated with an elevated risk of myocarditis, the risk ratio was 3.24, lymphadenopathy the risk ratio was 2.43, appendicitis the risk ratio was 1.4 and herpes zoster infection.  

However, SARS-CoV-2 infection was associated with a substantially increased risk of myocarditis, risk ratio 18.28 and of additional serious adverse events including pericarditis, arrhythmia, deep-vein thrombosis, pulmonary embolism, myocardial infarction, intracranial haemorrhage and thrombocytopaenia.  

This study concluded that in the nationwide mass vaccination setting, the BNT162b2 vaccine Pfizer was not associated with an elevated risk of most of the adverse events examined.  The vaccine was associated with an excess risk of myocarditis 

1 to 5 events per 100,000 persons.  The risk of this potentially serious adverse event and many other serious adverse events was substantially increased after SARS-CoV-2 infection.  

The London General Practice, the leading doctors’ Clinic in Harley Street commends the Government on its vaccination programme and encourages all those eligible to be vaccinated.

Dr Paul Ettlinger

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