After a discussion on the subject with the World Health Organisation (WHO), Public Health Minister Anutin Charnvirakul said on Friday that the frozen sample will be sent to the Department of Medical Sciences (DMSC) for analysis.
The department will then check to see if it can be developed into a vaccine or medicine.
"The vaccine was kept for 40 years and must be inspected to see if it can be beneficial. Even the WHO cannot tell if this vaccine can work against the current version of monkeypox," Anutin said.
Dr Kiatiphum Wongrajit, the ministry's permanent secretary, said the vaccine may still be effective as it can be cultured.
Separately, DMSC director-general Suphakit Sirilak said people likely to be infected will undergo an RT-PCR test for monkeypox. Samples will be collected via a nasal swab if there is no rash or from the rash excretion.
He added that some 10,000 doses of the vaccine had been frozen, and the department will take a while to see if it is safe and uncontaminated. It will also check to see if the vaccine can still provide some immunity.
He added that according to information dating back to the 1980s, this vaccine can provide 85-per-cent protection against smallpox, but he said this data was too old.
Also, he said, this vaccine came from a live virus so it could reproduce quickly, but the inspection process will take a long time and a committee will first have to be set up.
If there is a monkeypox case in Thailand, then the virus will be cultured to compare the immunity developed by people who received their smallpox jab in 1980.
As of Thursday, the number of monkeypox cases across the world rose by 35 to 344. The top five countries with the most cases are Spain with 120, followed by the UK with 77, Portugal with 49, Canada with 26 and Germany with 13.
Monkeypox was first discovered in 1958 when two outbreaks of a pox-like disease occurred among monkeys kept for research. The first human case of monkeypox was recorded in 1970 in Congo during a period of intensified effort to eliminate smallpox.