After being administered the vaccine, the patient developed thrombosis with thrombocytopenia syndrome, the commission's member Zoran Simonovič told the press on Tuesday.
The investigation confirmed the vaccination led to the vaccine-induced thrombotic thrombocytopenia in the woman, added Simonovič, head of Maribor's National Institute of Public Health (NIJZ) unit.
The woman died due to brain haemorrhaging and blood clots in what was the second case of serious adverse effects concerning Covid vaccines in Slovenia.
The country then suspended the use of Johnson & Johnson's single-shot vaccine on 29 September and appointed the commission of medical experts to examine the case.
The commission studied the patient's medical records from the moment she was admitted to the emergency unit of the neurology clinic at UKC Ljubljana hospital until the end of her treatment at UKC Ljubljana.
It also studied the medical file obtained from the patient's GP, which however showed no condition that could signal problems after the vaccination, said Simonovič.
Unlike in several other countries where the Janssen vaccine is administered only to older patients, it was available to all adults in Slovenia bar pregnant women. A total of 120,000 Slovenians have been vaccinated with it.
The vaccine surged in popularity after the government decided those vaccinated with it qualified for the Covid pass as early as a day after receiving the shot. For all the other vaccines, the Covid pass took effect after the second dose.
Upon suspending its use, the government made the vaccine available only on a person's specific demand accompanied by a written consent, which Health Minister Janez Poklukar said today would be made into a new, permanent rule.
Asked by a journalist whether the country could stop or limit the use of AstraZeneca's vaccine, the other viral vector vaccine, he said the government would follow the expert opinion.
Bojana Beović, the head of the national advisory committee on immunisation, said several options were possible, with one being limited use of both vector vaccines upon explicit wish of an individual or counter-indications after vaccination with mRNK vaccines.
Another option is limiting the use of the AstraZeneca vaccine this way, and completely banning Janssen, and the third option is full ban on the use of both vaccines. "This is a matter of agreement within the advisory committee," Beović said in a separate statement to the press.
Borut Štrukelj, a professor at the Ljubljana Faculty of Pharmacy, said that the woman had been vaccinated on 16 September with a dose with the serial number XE 393.
He said the vaccine is used in most European countries, Canada and the US, while US statistics have shown 1.2 persons per 100,000 - mostly women aged 30 to 37 - developed this adverse side effect.
Until 30 October, 16.3 million Janssen jabs were administered in Europe, and six deaths related to this vaccine beyond doubt were recorded, said Štrukelj.