The short answer is that we got very lucky with COVID-19 because the iconic spike protein of the SARS-CoV-2 virus that is contained in the mRNA vaccines is not only targeted by antibodies, which detect the virus before it infects a cell but also by T cells, which can destroy cells that have been infiltrated by the virus.

So when antibody levels produced by your vaccination wane to levels that cannot prevent infection, the T cells are still able to clear an infection rapidly to prevent the development of severe disease. In some cases, where the T cells are produced at high levels, the infection could even be aborted before you show any symptoms.

But not all viruses have components that can be targeted by antibodies and T cells. For example, antibodies and T cells, especially killer T cells, target different parts of the dengue virus. So an mRNA vaccine composed of just the envelope protein of the dengue virus would trigger the production of antibodies but not killer T cells. Therefore, the level of protection against dengue for such a vaccine would be less than what we have witnessed for COVID-19.

Other pathogens may have more complex biology and possess genetically encoded mechanisms to evade immune responses. Taken collectively, vaccine development remains challenging for many human pathogens and can only be resolved through continued research.

Burn injuries can be caused by many things including high heat, extreme cold, electricity, chemicals, friction or radiation. Depending on the time and intensity of the exposure, the burn damage to tissues and cells can vary.

The severity of burns is classified based on the depth and area of injury. Depths of burns are categorised into superficial, superficial partial-, deep partial- and full-thickness injuries where the damage starts from the top layer (epidermis) to the second layer of skin (dermis) followed by the subcutaneous fat, muscle and even bone in the most extreme cases. 

Burns are different from other cutaneous wounds with three distinguished zones of injury on the surface. The innermost zone of coagulation is the primary site of injury that consists of damaged tissue where all the cells rapidly undergo necrosis—a condition in which body tissues die due to a lack of blood supply. The middle zone of stasis is a region consisting of partial-thickness skin damage along with some cellular damage and restricted blood flow (ischemia) where the injury is potentially reversible with proper and timely intervention. Finally, the outermost zone of hyperemia is characterised by swelling and redness caused by inflammatory responses to the injury. In this zone, innate immune responses are stimulated by the activation of neutrophils, monocytes, macrophages and T cells to protect the injured tissue from pathogens.

Eventual healing comes about after a complex cascade of overlapping processes that first involves the immune cells in the inflammation phase fighting infection, followed by the reconstitution of the damaged tissue layers through the recruitment of skin cells in the proliferation phase; and finally, the remodelling phase where the newly-developed tissue matures strengthens and stabilises.

Clinical Associate Professor Alvin Chua
SingHealth Duke-NUS Musculoskeletal Sciences Academic Clinical Programme