In May 1767, Maria Theresa celebrated her 50th birthday but an epidemic was coming to the household. Maria Josepha of Bavaria, her daughter-in-law, was the first one to fall ill and Maria Theresa was with her when she received the diagnosis. She stayed to comfort and kiss her, but then came down with smallpox herself.
Within a week there were serious concerns for her life, and there were days of extreme crisis, and at the height at of one them, Maria Josepha died. Maria Josepha’s husband was not by her side when she died, and he did not attend her funeral. Instead, he spent his days and nights by his mother’s bedside. He left her only to sleep for a few hours in the adjoining room. The rooms around Maria Theresa room were filled with family members who had survived the illness and were thus immune. Crowds of people had begun to gather around the Hofburg, and every church in the city of Vienna joined in services of prayer. Even her son-in-law, Albert of Saxony, came to pay his last respects to a beloved mother-in-law. He too came down with the disease.
At last, Maria Theresa appeared to be out of danger. She emerged in public to take part in a thanksgiving service in the St. Stephen’s Cathedral to cheering crowds. Vienna remained ridden with the disease and in it had not yet finished with the royal family. In October 1767 her daughter, another Maria Josepha, also died of the illness. In total, Maria Theresa would lose four children to smallpox. Her daughter Maria Elisabeth was scarred by smallpox, making her unfit for marriage. Maria Theresa became a strong supporter of inoculation and had all her remaining children inoculated. She even hosted a dinner for the first 65 children in Vienna to be inoculated.