44 V oo ll uu mm ee 11 66 ,, II ss ss uu ee 21 ,, 22 00 22 11 C a n a d i a n J o u r n a l o f G e n e r a l I n t e r n a l M e d i c i n e
Message from the Editor-in-Chief
COVID-19, Vaccines and the Emergence
of a New Disease
The COVID-19 pandemic has taken on several twists and turns
amid undulating waves of infectious spread related to the emergence
of variant virus strains. There have been many surprises along the
way. Foremost has been the spectacular performance of the vaccines,
in most cases having >90% efficacy to prevent viral spread. Most
vaccinologists did not anticipate such a positive outcome as leading
figures in this field considered 50% efficacy as acceptable.
Like any drug product, vaccines come with potentially
serious adverse effects such as anaphylactic reactions, immune
thrombocytopenic purpura, and Guillaine-Barre syndrome.
This issue of the Journal highlights a newly-described vaccine
adverse effect that appears to be specific to the adenovirus vector
vaccines, and although extremely rare, can be life-threatening:
vaccine-induced thrombotic immune thrombocytopenia or VITT.
VITT has garnered front-page headlines internationally when
first discovered in March 2021 and has since been reported in many
countries that have adopted the ChAdOx1 nCoV-19 (AstraZeneca)
vaccine. More recently, VITT has also been reported to occur in
association with the other adenovirus vector Ad26.COV2.S (Johnson
& Johnson) vaccine.
How common is VITT? The true incidence, based on most
recent reports, is probably between 1 per 50,000 and 1 per 100,000
vaccinations. During ‘normal times, such vaccines would never have
passed muster for use because of this safety signal but in the face
of an uncontrolled pandemic, their high efficacy and overall safety
allows them to confer far more benefits in the form of infections
prevented, hospitalizations averted and lives saved from COVID-19.
Indeed, vaccines provide the light at the end of the pandemic tunnel.
How severe is VITT? As described in the report by Tejpal et
al., VITT is a medical urgency (in some cases an emergency) that
requires prompt diagnosis and appropriate treatment. VITT
is a
highly prothrombotic
disease with potentially devastating clinical
consequences. The
initial case fatality rate was reported as 40%
whereas more recent
estimates indicate a fatality rate of about
20%. With increasing
familiarity about how to diagnose and treat
VITT, it is likely this
mortality rate will drop further. As with
other heparin-induced thrombocytopenia (HIT) forms, heparins
should be strictly avoided, as should platelet transfusions, but unlike
conventional HIT, treatment is anchored on a combination of
immune globulin and non-heparin anticoagulants such as direct
anticoagulants or fondaparinux.
Where do I learn more about VITT? New resources have been
developed by the Ontario Science Table (https://covid19-sciencetable.
ca) and Thrombosis Canada ( to help
recognize diagnosis and treatment of VITT.
Although the administration of adenovirus vector vaccines is
declining in Canada (and may be curtailed altogether), their use will
increase in many other countries. In addition, the rapid dissemination
of knowledge related to VITT, including the contribution by Tejpal
et al., will allow clinicians to be best positioned to diagnose and
treat VITT while we emerge from the pandemic tunnel.
James Douketis, MD
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