The majority of adults and senior citizens who were vaccinated against smallpox will have no immunity to monkeypox, according to the Department of Medical Sciences.
Fortunately, vaccination is not being called for at the moment as the rate of infections and mortality is still low and personal preventive measures alone are still adequate, Dr Supakit Sirilak, the department's chief, said on Monday.
Speaking at a Ministry of Public Health press conference, Dr Supakit revealed that laboratory tests on citizens aged over 40 who received the smallpox vaccine when they were younger had proven no strong correlation.
The department used the Plaque Reduction Neutralization Test (PRNT) method on serum from the 30 smallpox-vaccinated volunteers aged between 45-74 years.
The two diseases have certain similarities, which is why the smallpox vaccine has been deployed to fight monkeypox until a viable bespoke vaccine can be brought to market, he said.
"We have found that 28 of trialists had no immunity against monkeypox, although one had maintained immunity level against the disease's A.2 variant and another against both B.1 and A.2 variants," he said.
"However, overall results led to the conclusion that the majority of older Thai citizens has no marked immunity against monkeypox."
However, he insisted that there is no rush to develop a vaccine because the global rate of infection remains so low, with 50,327 cases and 15 deaths in over 100 countries, since the World Health Organization (WHO) announced it as a Public Health Emergency of International Concern (PHEIC) on July 23 this year.
He said the current smallpox vaccine also has some unpleasant cardiological and neurological side effects which is a concern. However, the first lot of 1,000 doses of smallpox vaccine should still be given to health workers and people with a high risk of infections as a precautionary measure.
He added that it is clear that very-close person-to-person skin contact is the major cause of infections, so frequent hand washing and social distancing remain the best practice for now.
Thailand has placed an order for 1,000 doses of smallpox vaccine under the commercial name of Jynneos vaccine from the United States, which is enough for 500 people. The Department of Disease Control will later make it clear who will receive the shots.
Dr Supakit said that while the National Vaccine Institute and universities work on an officially recognised activated formula, a traditional inactivated vaccine would be the best option at the time being.
There have been seven confirmed cases of monkeypox in Thailand.