I read with concern Forum writer Lee Chun Yii's letter (Little is known about the long-term safety of Covid-19 vaccine, Feb 26).

There are several points which indicate a misunderstanding of how the virus causes disease, how the mRNA vaccine works and the epidemiology of Covid-19.

First, getting Covid-19 has long-term consequences. From what is now better known, a significant minority of patients ranging from 10 per cent to 40 per cent may suffer from long-term complications affecting the heart, brain and lungs, and general well-being. This is called the "long Covid" syndrome. In contrast, no major safety concerns have emerged despite millions of people being vaccinated across the world.

Second, mRNA vaccines work by stimulating the production of the spike protein within our cells, which then stimulate antibody production and other immune cells that protect us from future infection. There are many advantages of these mRNA vaccines.

The mRNA vaccines currently available are the most effective vaccines that all future Covid-19 vaccines need to contend with as the gold standard. Additionally, the technology also allows quicker updates within weeks rather than months when significant new strains require an update.

There is no virus in the mRNA that can bind to ACE2 receptors to produce any long-term complications. However, unvaccinated people getting Covid-19 are at risk of long-term complications.

Where there is paucity of safety data, such as in pregnancies and in children, Singapore has been cautious and has held off recommending the vaccine until further data emerges. Hence, these vaccines are recommended only when there is good evidence to show that benefits outweigh the risks.

It is true that young people are at lower risk of complications. But it is not zero risk. Data from Europe and North America suggest 1 per cent to 5 per cent still died from Covid-19.

Importantly, young people with Covid-19 and actively socialising are responsible for the spread of the disease and contributing to the rapid spread of new strains. Notably, they infected the high-risk older people or those with medical problems who then died from Covid-19.

For personal and family reasons, and as good citizens of a society, young people should also take Covid-19 vaccines when offered. Delaying effective Covid-19 vaccination has real negative societal consequences, especially when we are progressively opening up society and the economy.

David Lye (Associate Professor)

Director, Infectious Disease Research and Training Office, National Centre for Infectious Diseases

Member, Expert Committee on Covid-19 Vaccination