Commentary: COVID-19 vaccine deaths a reminder that benefits of vaccination must outweigh risks of side effects

LEARNING FROM SMALLPOX AND POLIOMYELITIS

History offers two examples with which to consider the risks and benefits of COVID-19 booster shots.

Smallpox was a dreaded acute viral disease in the 18th century. As many as 30 per cent of smallpox patients died, and of those who survive smallpox, about 80 per cent had to live with pitted scars on the face and bodies for the rest of their lives.

Edward Jenner’s discovery that cowpox virus infection protected against subsequent smallpox virus infection began an era where people could be intentionally protected against specific infectious diseases.

However, smallpox vaccination was associated with smallpox-like disseminated skin lesions and deaths in 1.5 and 1 in a million vaccine recipients, respectively. This risk is comparatively small when viewed against the 30 per cent probability of dying from smallpox at a time when it was raging through Asia, Europe and the rest of the world.

With the eradication of smallpox, smallpox vaccination also ceased a few years later. Children born in Singapore from 1982 onwards were no longer required to be vaccinated against this disease. Where there is no disease, anywhere in the world, vaccination offers no benefit.

Another case in point is poliomyelitis, which can result in lifelong paralysis of affected people in about 1 in 100 infections.

The oral polio vaccine provides superior protection compared to the injected polio vaccine. It is also cheaper and easier to administer.

However, the oral polio vaccine is composed of weakened but still live polioviruses and can cause polio-like paralysis in 1 in 2.7 million vaccinations. When poliomyelitis was common, the benefit of preventing disease greatly outstripped the small risk of severe adverse events.

With poliomyelitis having been eliminated in most parts of the world, the risk of vaccine-associated paralysis became unacceptably high. Singapore, like many countries, has switched fully to the injected form, which is composed of killed polioviruses and has no risk of paralysis.