In the early 1800s, a unified effort by Denmark's government, medical community, church, and educators led to the rapid elimination of smallpox in Copenhagen. The campaign achieved 90 percent vaccination rates among children by 1810, making Denmark Europe's most vaccinated nation per capita at the time. This success offers insights into building trust for modern vaccination drives.
Smallpox, a disease that killed three in 10 infected individuals and scarred or blinded many survivors, had claimed over 12,000 lives in Copenhagen in the half-century before 1808. The vaccine, invented by English physician Edward Jenner in 1796, reached Denmark swiftly, exciting the medical elite. Henrich Callisen, a prominent Danish physician, noted the 'excited attention and expectation' it sparked.
The first vaccinations occurred soon after: the child of a Danish judge, followed by a bishop's child. Reports highlighted its effectiveness; vaccinated individuals could share beds, clothes, or even breastfeed from infected mothers without contracting the disease, according to Callisen. In 1801, the King of Denmark established a vaccine commission to distribute the vaccine widely and track rates and cases.
Andreas Eilersen at Roskilde University and colleagues analyzed these records, finding that by 1810, 90 percent of Copenhagen's children were vaccinated. This led to smallpox's disappearance from the city just seven years into the campaign. Callisen wrote in 1809: '[We] will be freed from one of the most terrible and destructive diseases we know.'
Key to success was free access for the poor, plus promotion by church leaders and teachers alongside doctors. One priest vaccinated 1,981 children in a single year. To sustain rates as the disease waned, the commission in 1810 required vaccination for children's church confirmation, countering fears of complacency.
Some resisted due to 'ignorance and prejudice,' but most embraced it. Callisen, initially wary, became convinced of its benefits for 'human wellbeing and happiness, and on increasing population and national strength.' Eilersen attributes the high uptake to a united front: 'Basically, we had a bunch of different authorities – the government, the medical establishment and the church – that all agreed on what to do.' This collaboration convinced the broader population.
Denmark's high institutional trust persists today, ranking first globally per Transparency International, correlating with 96 percent childhood vaccination rates for diphtheria, tetanus, and pertussis—far above the US's 80 percent.
The study appears in medRxiv (DOI: 10.64898/2026.01.05.26343436).
