According to your standards of what's effective and what isn't, yes.
https://en.wikipedia.org/wiki/1972_Yugoslav_smallpox_outbreak
>By 1972 the disease was considered to be eradicated in Europe. The population of Yugoslavia had been regularly vaccinated for 50 years, and the last case was reported in 1930.
>In early 1972, a 38-year-old Kosovo Albanian Muslim clergyman named Ibrahim Hoti, from Damnjane near Đakovica, Kosovo, undertook the Hajj.[5] He visited holy sites in Iraq, where cases of smallpox were known. He returned home on February 15.[6] The following morning he suffered aches and was tired. After feeling feverish for a couple of days and developing a rash, he recovered,[7] likely because he had been vaccinated two months earlier.[8]
>On March 3, Latif Mumdžić, a thirty-year-old teacher, who had just arrived in Đakovica to attend school, fell ill. He had no known direct contact with Hoti. He may have been infected by one of the clergyman's friends or relatives who visited during his illness, or simply by passing the clergyman in the street. When Mumdžić visited the local medical center two days later, doctors attempted to treat his fever with penicillin (smallpox is a virus, so this was ineffective). His condition did not improve, and after a couple of days, his brother took him to the hospital in Čačak, 150 km to the north in Serbia. The doctors there could not help him, so he was transferred by ambulance to the central hospital in Belgrade. On March 9, Mumdžić was shown to medical students and staff as a case of an atypical reaction to penicillin, which was a plausible explanation for his condition. On the following day, Mumdžić suffered massive internal bleeding and, despite efforts to save his life, died that evening.
>Mumdžić's brother developed a smallpox rash on March 20, resulting in medical authorities realizing that Mumdžić had died of smallpox. The authorities undertook massive revaccination of the population, helped by the World Health Organization (WHO), "almost the entire Yugoslavian population of 18 million people was vaccinated". Leading experts on smallpox were flown in to help, including Donald Henderson and Don Francis.[12]
>By mid-May, the outbreak was contained and the country returned to normal life. During the epidemic, 175 people contracted smallpox and 35 died.[13]
In short;
- Yugoslavia was vaccinating everyone against smallpox
- Ibrahim Hoti visited Iraq where smallpox was still out and about, therefore took a booster vaccine 2 months before, still caught the virus and got sick but easily recovered
- Latif Mumdžić, who was vaccinated against smallpox like everyone else in the country was the first serious case 2 weeks later, he was not medicated for smallpox because doctors misdiagnosed him and died in a week
- ENTIRE POPULATION OF YUGOSLAVIA was given a booster shot, no exceptions accepted, the next month
- even though everyone in the country (at least everyone younger than 50) was vaccinated, 175 got sick and 35 died before the outbreak was contained WITH BOOSTER SHOT
all in all:
the smallpox vaccine works exactly like the covid vaccine which you claim doesn't work