The light at the end of the pandemic tunnel was marred by a worrying shadow. As the COVID-19 vaccines were rolled out, headlines fuelled anxiety: some people were developing life-threatening blood clots after receiving either the Johnson & Johnson vaccine (made by one of its subsidiaries, Janssen Vaccines) or the Oxford-AstraZeneca shot. This serious complication was almost only seen with these two vaccines, although one person who received the Moderna vaccine and one who was vaccinated with the Pfizer shot also received the same diagnosis.

The anti-vaccine movement took this real observation and stretched it out of proportion, accusing all COVID vaccines of killing large swaths of the population through deadly coagulation.

The actual issue was very rare and quite narrow, though still distressing. Based on a survey of what was reported in the scientific literature, 137 people worldwide are known to have died from blood clots following COVID vaccine injection, six of whom died in Canada. Shortly after the problem was identified, health authorities revised their vaccine recommendations. Johnson & Johnson halted production of its vaccine in February 2022; AstraZeneca withdrew its vaccine worldwide in May 2024.