Omicron
Compared to Delta, Omicron showed signs of a much greater ability to infect people who have some existing protection [from vaccination and or past infection] due to what experts call “immune escape” properties. Image Credit: AP

Highlights

  • Experts point to Omicron as being more efficient in infecting people, even those previously infected/vaccinated, due to its "immune escape" properties.
  • A 33-member UK panel of scientists cite multiple analyses showing Omicron's ‘intrinsic severity’ is like to be lower than that of Delta.
  • This hypothesis comes with many caveats, and with only a ‘medium confidence’, due to current lack of data.

DUBAI: COVID cases are rising across the world. Omicron has demonstrated a doubling time of around 4 to 5 days, said experts in a panel discussion on December 23, in their notes released on Christmas Eve.

One important point from the 33-member experts panel: the combined rollout of booster vaccines remains a critical factor alongside the new antiviral drugs.

This will be particularly useful for vulnerable individuals — elderly among them. There is no question now that Omicron is en route to dominating Delta. Infectious disease experts are trying to figure if Omicron does have less “intrinsic severity” than previous variants.

Booster shots

Booster vaccine rollout remains very important. Antiviral drugs will be particularly useful for vulnerable individuals,” the 33-member expert panel said.

Here’s what we know so far:

Does Omicron have less “intrinsic severity” than Delta or prior variants?

An updated report from the UK’s (SAGE) Scientific Advisory Group for Emergencies  group noted that "the number of Omicron infections continues to grow quickly”.

There are emerging reports that among Omicron-positive patients, the loss of taste/smell has been reported less. the experts noted, however, that there is less frequent loss of smell/taste among patients that contract the new strain. They also noted in-lab lung cell infectivity, citing the latest British health data.

Omicron
Omicron Image Credit: AP

“Although there is an apparent slowing of growth rates, the UK Health Security Agency (UKHSA) data suggest doubling times in most of the country are still in the region of 2 to 3 days and, importantly, test positivity rates are still rising."

The online session teleconference delved into several possible scenarios, given what is currently known with Omicron:

  • “Intrinsic severity” (or less severity)
  • Infection rate
  • Hospitalisation rate

Current estimates in those infected range from a 15% to an 80% reduction in the risk of hospitalisation, the experts pointed out.

“The extent of the difference will be an important determinant of the scale of the upcoming wave of hospitalisations,” the experts’ discussion notes stated. While studies focus primarily on likelihood of hospitalisation — this is only one measure of severity, they pointed out.

There are at least 4 recent studies out on Omicron. Given the spike in infections and rising test positivity rates, however, there still remains a high degree of uncertainty as to the extent of the difference between Omicron and Delta, the experts said, citing that the current data available is “preliminary” at best.

What’s the difference between Omicron's effect on younger vs older people?

The number of people in hospital with Omicron infection continues to increase with a doubling time of around 4 to 5 days, the scientists noted. The infections have been concentrated in younger age groups to date. Experts warned, however, that hospitalisation rates will increase as older age groups are infected.

“As infections move into older age groups, a large wave of hospital admissions should be expected,” the SAGE group added.

israel booster-1632559986812
A 14 year-old Israeli receives a booster shot of the coronavirus vaccine at Clalit Health Service’s vaccination center in the Cinema City complex in Jerusalem, Wednesday, Sept. 22, 2021. Israel is steaming ahead with its aggressive campaign offering coronavirus booster shots to almost anyone over the age of 12, even after a U.S. government advisory panel called for limiting them to patients who are older or at higher risk.(AP Photo/Maya Alleruzzo) Image Credit: AP

Would the current holiday season trigger a spike in cases?

Experts said the data will be “unreliable” over the festive period — as testing and hospital admission patterns change. This will make it difficult to interpret any apparent trends over the next few days.

While the apparent fall in the rate of growth may be a genuine slowing related to changes in mixing patterns or behaviours (for example people reducing risk prior to the festive period), other factors could also be at play.

“It could also be related to different rates of spread amongst different groups — or to a reduction in the remaining number of susceptible people in some sub-groups,” they added.

Changes in testing behaviours in the lead up to the holiday weekend are also a possible factor, in which case it may not be a genuine slowing.

What does “lower intrinsic severity” of Omicron mean?

It simply refers to what until now is only a hypothesis that Omicron is really less severe than previous variant, especially Delta.

The experts, citing multiple analyses, suggest that it is likely that the “intrinsic severity” of Omicron is lower than that of Delta. This observation, however, comes with only a “medium confidence”.

They stated that recent studies focus primarily on the likelihood of hospitalisation — though this is only one measure of severity. “There remains a high degree of uncertainty as to the extent of the difference (between intrinsic severity vs realised severity.”

15% to an 80%
Estimates of reduction in the risk of hospitalisation among those infected with Omicron, vs Delta.

Going forward, the extent of the difference will be an key determinant of the scale of the upcoming “wave” of hospitalisations, they added, referring to the UK cases.

Is there a big difference between Omicron and Delta?

Experts cited “some laboratory evidence of biological differences” between the two variants of SARS-CoV-2. This includes viral-entry mechanisms.

“These might provide a plausible explanation for Omicron infection being less intrinsically severe than Delta,” they added.

“Anecdotal Evidence”
The scientists only cited “anecdotal evidence” which suggests reduced severity of illness for those with Omicron infection attending hospital — though it’s mostly younger patients at the moment.

This gives the experts a low confidence in the data. Moreover, thresholds for hospital admission tend to change as hospitals get busier and so the case mix in hospitals may change over the course of the wave.

The most dependable data on severity in hospital will be the number of patients requiring oxygen. Currently, they said, the number of people requiring oxygen is fairly stable.

One important note: The experts did point out that “re-infections are likely to be less severe than first infections. This means that realised severity (the severity observed in a population depending on background rates of immunity and other factors that modify disease severity) will be lower than for Delta. This effect is in addition to the impact of lower intrinsic severity.”

Is age a factor in the severity of Omicron?

The most important factor in determining the proportion of infected people who go on to be hospitalised in this wave will be the age profile of those infected. Scientists are unable to give a definitive yet: There’s still limited evidence as to how the “intrinsic severity” and “realised severity” may vary across age groups.

Evidence to date is primarily from younger (but unboosted) people. Realised severity will also be dependent on vaccine effectiveness against Omicron and how this differs by age and over time; evidence is still emerging on this.

Omicron
The most important factor in determining the proportion of infected people who go on to be hospitalised in this wave will be the age profile of those infected. Scientists are unable to give a definitive yet: There’s still limited evidence as to how the “intrinsic severity” and “realised severity” may vary across age groups.

How bad will this “new wave” of infections with Omicron get?

The experts said besides the uncertainty about Omicron’s intrinsic severity, several sources of uncertainty remain about the scale of the anticipated wave of hospitalisations. These would depend on the following factors:

  • The impact of behaviour change (for example mixing patterns and use of testing), especially over the festive period
  • Waning of immunity, and
  • The generation time of Omicron.

There is considerable uncertainty as to how mixing patterns might change during and after the festive period. Continued availability of lateral flow tests will be important to enable people to reduce risk of transmission.

What is “generation time”?

Generation time is a particularly important factor; if it were to be shorter for Omicron than for Delta and therefore part of the reason for the rapid growth, the anticipated wave would be smaller, and interventions would have greater effect. There is currently no evidence on whether Delta and Omicron have different generation times. Generation time will also depend in part on behaviours.

What would be the peak level of hospital admissions with Omicron?

The panel pointed to a “high uncertainty” in terms of level of peak in admissions with Omicron. Even with a reduction in intrinsic severity of the variant, they anticipate that the peak may still be “comparable to or higher than previous peaks in the absence of significant behaviour change or further interventions.”

On the other hand, occupancy will depend on admissions and will also scale with length of stay — which may be reduced but there are no firm data yet.

Is it possible to determine the wave of hospitalisations vs the wave of infections, especially in older age groups?

Not at this point, they added. The time and scale of the wave of hospitalisations will depend primarily on the timing of the wave of infections in older age groups.

“It is not possible to predict when this will be, particularly given changes to mixing patterns” over the Christmas holiday period, they said. But such a wave should be expected soon. The reason: infections are increasing rapidly in all age groups and regions.

"Some epidemic waves peak below their theoretical maximum, which can happen for several reasons including because of local networks building up high levels of immunity. When this happens, the epidemic may increase again later as infection finds its way into other networks with more susceptible people."

Omicron thrives in airways
Image Credit: Seyyed de la Llata, Senior Designer