What we know about the Omicron and Delta variants

The Omicron variant is becoming a better known enemy, with more data available now.

So far, Singapore has seen 2,252 Covid-19 cases caused by the Omicron variant.

In the past week, the incidence of Omicron cases has risen sharply, with the Ministry of Health (MOH) detecting 1,281 cases comprising 1,048 imported cases and 233 local, director of medical services Kenneth Mak said at a virtual press conference by the multi-ministry task force on Covid-19 yesterday.

Omicron cases comprise an average of about 18 per cent of all Covid-19 cases reported to MOH, and the proportion will rise further, driven by its high transmissibility compared to Delta and other variants.

Here are some differences between the variants.

At its peak, Delta infections were doubling every six to eight days. On the other hand, Omicron infections may double in just two to three days, said Health Minister Ong Ye Kung.

The next wave may be bigger than the Delta wave that Singapore dealt with in October and November, said Associate Professor Mak.

At Delta's peak, MOH saw case numbers reaching about 5,000 in one day, but the number associated with an Omicron wave may far exceed this, perhaps reaching 10,000 or even 15,000 in a worst-case scenario, he added.

This concern is consistent with the experience seen in other places such as Britain, Denmark, other European countries and South Africa, said Prof Mak.

This is particularly so among the vaccinated and even more so among those who have received their booster shots, and is consistent with international data and what Singapore has been witnessing, Mr Ong said.

So far, Singapore has had 2,252 Omicron cases. Out of these, only three required oxygen supplementation, and all three were taken off oxygen within three days.

None of the Omicron cases has been hospitalised in the intensive care unit (ICU) so far. If the 2,252 cases had been infected by the Delta variant, Singapore would have had about 30 individuals requiring oxygen supplementation, being hospitalised in the ICU or die, Mr Ong said.

Despite the relatively lower risk of severe infection from Omicron, the overall high numbers of infection could mean a significantly higher absolute number of hospitalisations, as seen from the experience of other countries such as Britain, Prof Mak said.

Even if the ICU occupancy in hospitals remains manageable, the situation could be further compounded by a larger proportion of healthcare workers getting infected when they are exposed to infection in their own households, and need to be placed on medical leave, a situation that has been reported in Britain, he added.

Although there is lower vaccine efficacy against Omicron compared with Delta, vaccination still provides a protective benefit against Omicron, especially among those who have had their booster shots, Prof Mak said.

Noting that vaccination and boosters offer protection against both variants, he urged those who are eligible to get the shots as soon as possible.

However, there is an increased risk of reinfection from Omicron among people who have previously recovered from Covid-19 infection, Prof Mak said.

A preliminary study by South African scientists published on Dec 2 suggests Omicron is three times more likely to cause reinfections compared with the Delta or Beta strain.

The findings, based on data collected by the country's health system, provides the first epidemiological evidence about Omicron's ability to evade immunity from prior infection. The paper has not yet been peer-reviewed.