A letter from Catherine the Great supporting mass immunization against smallpox sold at auction Wednesday in London. In the letter, dated April 20, 1787, the Russian empress instructs a governor-general of what is now Ukraine to make immunizing the public a priority and says that “such inoculation should be common everywhere.”

The letter sold at the MacDougall’s auction house along with a portrait of the empress painted by Dmitry Levitsky, for a total of ₤951,000. MacDougall’s said the letter reveals “the statecraft and foresight shown by the great monarch.”

It also shows her struggle against fear and misinformation about immunization among the public. Nearly two decades before the letter was written, she had become the first person in Russia to be immunized against smallpox, yet millions of Russians still feared the procedure.

The modern smallpox vaccine, which used the cowpox virus, was developed by British doctor Edward Jenner in 1796. In the decades before that, a method of immunization called variolation proliferated. In variolation, pus or scabs from a person with smallpox were introduced into the bloodstream of a patient, usually via cuts on the arm. The patient would then develop a milder form of the disease and would be immune after recovery.

Unlike modern vaccines, which are safe, variolation had a death rate of about 2 percent, which was better than the 30 to 40 percent death rate typical in smallpox outbreaks, but still risky.

In the United States, the variolation technique was introduced in the early 1700s by an enslaved African man named Onesimus, who told his enslaver, Puritan minister Cotton Mather, about a technique he said Africans had been using for hundreds of years. Supporters of the method included Benjamin Franklin, John Adams and George Washington.

In Russia, immunization came a few decades later via the empress. Like most people on the planet at the time, Catherine had been stalked by smallpox throughout her life: Her future husband came down with it the day before their wedding, and the spring before she was immunized, she had feared for her son’s life after yet another smallpox outbreak hit St. Petersburg, she wrote in a letter to the King of Prussia.

“I was advised to inoculate my son with smallpox,” she wrote. “I used to reply that it would be shameful not to start with myself, and how could I introduce smallpox vaccination without setting a personal example?”

Catherine summoned to St. Petersburg the British doctor Thomas Dimsdale, who claimed to have developed a variolation technique with a much lower death rate; in fact, he had successfully immunized the entire British royal family. For weeks, he was lavishly wined and dined while the empress followed the pre-variolation diet he recommended. Then, one night in October 1768, a sleeping child sick with smallpox was wrapped in a quilt and brought to the palace, where Catherine was inoculated in secret.

A heavily fictionalized version of Catherine’s immunization is depicted in season 1, episode 7 of the Hulu show “The Great.”

The next day, she and Dimsdale moved to her summer palace, where the empress hoped to convalesce under the radar. She also kept a fast carriage at the ready just in case she died, so Dimsdale could escape reprisals from her people.

“She has had the smallpox in the most desirable manner, a moderate number of pustules, and complete maturation,” he soon recorded. “Which now, thank God, is over, and I find an inexpressible load of concern removed from my breast.”

Her full recovery was announced to the world on Oct. 29, 1768. There was a national celebration, an allegorical ballet called “Prejudice Defeated” was staged and Dimsdale was made a baron.

Soon, Catherine wrote in a letter to her British ambassador, “There is no noble house in which there are not several vaccinated persons, and many regret that they had smallpox naturally and so cannot be fashionable.”

But the letter sold Wednesday, written 19 years later, is not so triumphant. Many doctors remained skeptical of variolation, and clergy railed against it, saying it was akin to “playing God.” Most people remained unimmunized, and devastating outbreaks were still happening in Russia.

“Count Piotr Aleksandrovich,” she writes, “Among the other duties of the Welfare Boards in the Provinces entrusted to you, one of the most important should be the introduction of inoculation against smallpox, which, as we know, causes great harm, especially among the ordinary people. Such inoculation should be common everywhere, and it is now all the more convenient, since there are doctors or medical attendants in nearly all districts, and it does not call for huge expenditure.”

She gives him detailed instructions to house people convalescing after getting the procedure in abandoned convents and monasteries and tells him how to pay for the campaign using local taxes.

“We remain, by the way, favorably disposed towards you,” she closes, before signing her name with large flourish fit for an empress.