Singapore saw the first death of a fully vaccinated person on Tuesday from Covid-19 complications - a 90-year-old man with a history of other health issues.

Some patients who are fully vaccinated have also landed in the intensive care unit (ICU).

This has led some to ask: What is the point of vaccines if they do not guarantee that people will not get seriously ill with Covid-19?

Associate Professor Lim Poh Lian, a senior consultant at the National Centre for Infectious Diseases (NCID) and director of its High Level Isolation Unit, helps to answer some of these questions.

Q: What is the point of getting vaccinated if people can still end up in the ICU or even die of Covid-19 complications?

A: Recent data allows us to say clearly that vaccinated persons are less likely to die of Covid-19. They are also less likely to require oxygen supplementation or ICU care.

Moreover, vaccinated persons are less likely to get infected. If infected, they clear the virus faster and are infectious for a shorter time.

Large studies from overseas have clearly demonstrated that vaccinations reduce Covid-19 deaths, hospital admissions and ICU admissions, before the advent of the Delta variant. That protection against severe and fatal Covid-19 still holds true in the face of Delta's surge.

Q: What does a vaccine's efficacy rate mean?

A: When we cite vaccine efficacy rates, it is important to understand what is the outcome we are measuring.

Take a common vaccine like the chickenpox (varicella) vaccine. It is 90 per cent effective in preventing symptomatic chickenpox, but it is 99 per cent effective in preventing deaths from chickenpox.​

What does a 90 per cent-effective vaccine mean? It means that if I had 100 vaccinated persons exposed to an infectious case, up to 10 persons might catch chickenpox.

These "breakthrough" chickenpox cases happening in vaccinated persons are much milder than chickenpox in unvaccinated persons. Their fever gets better in a shorter time, they have fewer blisters, and they are much less likely to get the rare lung and brain complications of severe chickenpox.

The example of the chickenpox vaccine can be applied directly to understand Covid-19 infections that happen in vaccinated persons.

As an infectious disease doctor working at NCID since the start of this Covid-19 pandemic, I have seen the tremendous difference vaccination has made in reducing Covid-19 severity in the patients we are treating.

Q: What does recent data from the Ministry of Health show us about the effect of vaccination in Singapore?

A: As at Aug 10, 72 per cent of Singapore's population were fully vaccinated, and 81 per cent had received at least one dose of a vaccine, leaving 19 per cent completely unvaccinated.

There were 35 Covid-19 patients on that day sick enough to need oxygen supplementation. Of those, five were fully vaccinated, eight were partially vaccinated, and 22 completely unvaccinated.

If the fully vaccinated people (comprising 72 per cent of the population) had not been vaccinated, there would have been 83 on oxygen instead of five.

So vaccination potentially spared 78 persons from requiring oxygen supplementation.

These numbers actually underestimate the benefit of vaccination in older adults because a large proportion of the unvaccinated are children under 12, who have a lower risk of severe disease.

Q: How has the Delta variant changed the situation?

A: At this point, Delta has out-competed and displaced the original Covid-19 and other earlier strains to become the dominant circulating strain here and globally.

Delta upped the stakes by developing mutations which have increased its transmissibility through much higher viral loads.

Its mutations have also allowed it to partially evade protection from existing vaccines, with some vaccines being more effective against the Delta variant than others.

Recent data from an NCID study shows that although vaccinated persons who get infected start out with viral loads that are as high as unvaccinated persons, they are able to clear their virus faster by almost a week.

They are therefore infectious for a shorter time, potentially requiring a shorter duration of isolation and can be released to resume normal activities earlier.

Q: So even though many people here are vaccinated, there might still be deaths and infections among them?

A: As we continue to vaccinate as many people as are willing to be protected, and with future surges in this unpredictable pandemic, we will see vaccinated people get infected or even die.

But if we liken Singapore to a room, vaccination reduces the number of bullets ricocheting around the room.

If vaccination can reduce the number of bullets from 2,000 to 20 bullets ricocheting, any given individual is much less likely to stop a bullet.

That individual could well be a 90-year-old vaccinated man who would otherwise end up in the ICU, or a 36-year-old pregnant woman who succumbs to Covid-19.

Vaccine breakthroughs can and will happen, but post-vaccination infections are much less severe.