Mpox vaccine advised only for Thai high-risk groups

The question of whether the general public should receive the mpox vaccine has been addressed by Yong Poovorawan, head of the Centre of Excellence in Clinical Virology at the Faculty of Medicine, Chulalongkorn University.

Highlighting the limited availability and high cost of the vaccine, he recommended it primarily for high-risk groups, particularly men who have sex with strangers.

Yong Poovorawan stated that the currently used third-generation vaccines are theoretically safer than the first and second-generations. However, these vaccines are still new, and their side effects need to be monitored over time. Though monkeypox is not highly severe, the emergence of new strains outside Africa warrants attention.

The Ministry of Public Health recently disclosed that the first Clade 1b mpox (formerly monkeypox) patient in Thailand had close contact with 43 individuals, all of whom are now under surveillance. According to Yong, over 400 mpox cases have been reported in Thailand.

For the general public, including both children and adults, Yong advises against vaccination at this time. Instead, the vaccine should be reserved for high-risk groups, such as men who have sex with strangers and those travelling to areas where the disease is prevalent.

Yong also shared insights on the development of the smallpox vaccine, which has evolved to the current third generation. Historically, smallpox caused significant mortality until Edward Jenner observed that milkmaids who contracted cowpox did not get smallpox. Jenner used cowpox pustules to inoculate a child, effectively demonstrating immunity against smallpox.

Contamination risks

The first-generation vaccines used the vaccinia virus, inoculating cows and later harvesting the virus from the pustules formed on the cows. This method involved drying the collected lymph and later rehydrating it for human inoculation. Despite the rudimentary process and potential contamination risks, this method was used extensively until smallpox was eradicated.

Concerns about biological warfare prompted further vaccine development. Second-generation vaccines cultivated the virus in laboratory cell cultures rather than using cows. This method allowed for more precise control over the virus quantity and improved safety from contamination. However, this generation still relied on traditional inoculation methods, which could cause side effects, particularly in immunocompromised individuals.

The third-generation vaccines use the same vaccinia virus but attenuated to the point where it cannot cause disease in humans. Some versions even prevent the virus from replicating, reducing the risk of side effects. These vaccines require two doses, six months apart, and are currently under patent, making them expensive.

Despite improvements, all vaccines can cause side effects. Historical smallpox vaccines sometimes led to severe complications, such as encephalitis and myocarditis. While the third-generation vaccines are designed to minimize these risks, their relatively recent introduction means that long-term side effects are still being studied. Given their high cost and potential side effects, these vaccines are recommended only for those at high risk, reported Khaosod.