While epidemiological and infectious disease experts originally estimated that a vaccine for Covid-19 would, at the earliest, appear on the scene only in 12 to 18 months, optimistic projections are that we may now get such a vaccine even before the year's end (Finding a cure and vaccine for Covid-19, May 23).

If that happens, it might make one concerned about its safety and efficacy.

When regulatory thresholds are not strictly adhered to, animal studies are expediently compromised and safety profiles are glanced over, the prospect of suboptimal vaccines coming onto an expectant market looms.

Governments and Big Pharma continue to invest billions to develop a vaccine to inoculate against Covid-19. Together with the prestige and first-mover advantage that developing the first vaccine may bring are the pecuniary profits.

It has taken several months before a clearer understanding of Covid-19 has emerged and still we learn something non-intuitive about it every month.

It is likely that this will still be the case even after a vaccine is on the market.

The dilemma of the dengue vaccine comes to mind - with the virus occurring in four different serotypes, the vaccine can lead to severe problems in patients who have had a different strain before.

Covid-19 has different lineages and there is presently no guarantee that a vaccine developed in one part of the world where one lineage is predominant will work in other regions where different lineages are principal.

Singapore's Ministry of Health, through not adopting mass dengue vaccination, has saved us from any possible fallout. We have to rely on it again to perform all due diligence when a Covid-19 vaccine appears on the horizon.

Yik Keng Yeong (Dr)