Omicron Update (2)

Over the last few days, data has been published by the Government’s Scientific Advisory Group for Emergencies (SAGE) relating to the severity, transmissibility and more of the Omicron variant of Covid-19. BuDS has looked through this published data, and summarised the findings below. Read on for more.

This is a long article. There is a simple summary at the end of the post, which can be accessed through the contents below.



The most recent SAGE meeting, on 7 December, provides the best summary of the scientific data around Omicron in England. Below are the points made, simplified for easier reading.

  • The number of Omicron infections in the UK is now increasing rapidly, with evidence of community transmission. Hospital admissions should be expected to increase soon as well. This is estimated with high confidence. It was also stated that if unsustainable pressure on the NHS is to be avoided, tougher action will have to be taken very soon. 
  • Data suggests that the speed of growth in the UK is about the same as that seen in South Africa – which is very fast indeed. It is important to note that there are many differences between the UK and South Africa in how it is spreading, but it is still important to monitor the situation in South Africa as it can give a good indication as to what will happen here. There are reports that hospitalisations due to Omicron in South Africa are now increasing, which can be expected here as well.
  • The number of new suspected daily Omicron cases identified in the UK is now in the hundreds, and it is highly likely that the actual number of daily infections in the UK is in the thousands. This means that Omicron will be able to spread very quickly indeed, and increases the chance that any infected person you come into contact with could be infected with Omicron.
  • The doubling time for new Omicron infections is currently around 3 days in England. This means that the number of new daily cases of Omicron are doubling every 3 days, which leads to a very rapid exponential growth.
  • There is significant evidence that Omicron has a growth advantage over Delta (i.e. it is able to spread faster), including household studies which show higher secondary attack rates (i.e. more people are being infected by someone who has just caught Covid-19 than with Delta). There is more detail on this below from a UKHSA press release today (10 December).
  • The reasons why Omicron is spreading so much faster are unclear, but it is likely to be a combination of increased transmissibility and immunity evasion.
  • It is not yet known how many people infected with Omicron will go into hospital with it. More data is required to ascertain this, both on admissions and also on disease severity.
  • Initial data suggests that Omicron may cause less severe illness in those who are infected, though this is based on a very small data set from South Africa and should not be treated with confidence. It is likely to be linked to the fact that most people being hospitalised in South Africa are young people, who are historically less likely to have severe illness from Covid-19 (though the impact from Long Covid on them is often much worse). Even if it is less severe, however, the increased transmissibility and higher case numbers mean that the number of people in hospital will still increase.
  • Modelling suggests that at current growth rate, and with the current precautions, the number of hospitalisations from Omicron may reach 1,000 per day or higher in England by the end of the year (and still be increasing at that point). The overall peak that could be reached is unknown due to the potential impact of precautions and human behaviour, but it could easily be several times that. It is likely to reach around 1,000 to 2,000 Omicron hospital admissions per day without further intervention – for it to be below this level, SAGE estimate that there would need to be only a small degree of immunity resistance, and very high protection from boosters against Omicron. Both these points are unlikely, as is explained below.
  • The impact of changes in transmissibility and immunity resistance on overall numbers of hospital admissions is likely to be much more significant than the impact of any changes in severity. This means that regardless of how severe or not the illness caused by Omicron is, any reduction in hospitalisations due to this will be majorly outweighed by the increased transmissibility and high immunity resistance.
  • SAGE also predict other impacts from Omicron that aren’t public health related. An increase in deaths would have a large emotional impact on the population. An increase in hospitalisations would reduce the available workforce, making jobs a lot emptier and more difficult for those still able to work. More concerningly, the very rapid doubling times mean a large wave could occur, which would lead to many people being off work at the same time. This could lead to major disruption in all roles across the country, which would impact everyone.
  • The ‘Plan B’ measures introduced yesterday are NOT going to stop cases, hospitalisations and deaths increasing for several weeks. This is due to the lags between measures being introduced, these measures affecting infections actually occurring, and then this impact being reflected in hospitalisations.
  • It is highly likely that Omicron will account for the majority of new Covid-19 infections in the UK within a few weeks. Omicron may partially or largely replace Delta over this period, but this depends on how well each variant infects different groups in society (which is not yet known). It is possible that both Omicron and Delta could continue to spread at the same time, which would mean that the current levels of Delta infections and hospitalisations would be added to by those from Omicron. It is also possible that Omicron will completely replace Delta.
  • The time it takes for people infected with Omicron to be able to infect others is not yet known, but it is possible that it is shorter it is for Delta. This means that that case-based contact tracing, isolation if you are a contact, and other measures would become less effective at preventing the spread of Omicron, as people become infectious sooner. This would mean that measures that affect the entire population, such as a lockdown, would be a much better way of preventing the spread of Omicron.
  • Testing and self-isolation if you test positive still remains very important. If you are going to an event or place where you will meet others, testing beforehand can help reduce the risk of spreading Omicron.
  • Some international reports of ‘superspreader’ events suggest that airborne transmission is more significant for Omicron than it was for Delta. This is because it is less likely that Omicron could have spread to as many people as it has at those events by other routes As such, measures to reduce airborne transmission such as ventilation, well-fitting masks and social distancing are even more important.
  • Transmission within healthcare settings, such as hospitals, is likely to be an even greater risk due to Omicron, particularly as hospitalisations increase. Measures will need to be put in place to reduce this risk, to reduce the spread between healthcare workers, the spread between patients, and the spread between the two groups. Other vulnerable settings such as care homes and prisons are also at much higher risk than with Delta, for the same reasons.
  • Taking measures which slow or delay the wave of infections would allow more time for vaccination. This therefore allows for both increased numbers of people vaccinated and more booster doses being given. Data does not yet fully exist on how much vaccines or boosters protect against Omicron, but preliminary data should be available (according to SAGE) in the next week. Vaccine and immune effectiveness against severe disease is likely to remain higher than protection against infection as it does with Delta and other diseases.
  • Pharmaceutical treatments including antivirals will also continue to be important. Due to a lack of availability (as BuDS noted when their procurement was first announced), full use will not be possible in the next few months. In addition, there is a lack of clinical trial data, so we do not know how effective the antivirals will be when used.



Today (10 December), the UKHSA published a study into the transmission of Omicron, and vaccine efficacy against it.

The first major conclusion is that Omicron is much more capable of spreading than Delta, both in a household and among close contacts. Within a household, the risk of transmission is 3.2x higher than it is for Delta. For people who are close contacts of an infected person, the risk of transmission is 2.09x higher than for Delta. Finally, the household secondary attack rate (the rate at which an infected person infects others within their household) 10.7% higher than for Delta. These figures are very high indeed, especially considering how fast Delta has spread

It was also revealed that people who had two doses of the AstraZeneca jab 25 or more weeks ago (just under 6 months) have far lower protection against symptomatic infection with Omicron than they did against Delta. This means that if you had the AZ vaccine, then you are significantly unprotected against Omicron if you haven’t had a booster. According to the data, there should be about 40% protection against Delta at this time point (still scarily low), but crucially only 10% protection from Omicron. It is important to note, however, that these figures are not final – the study that made these conclusions had a relatively small sample size, and the AZ jab was given overwhelmingly to older and vulnerable people. That said, this makes it more important, as the most vulnerable people in society have the lowest levels of protection.

For those who received the Pfizer vaccine, there is a similar trend in protection waning. However, this is to a lesser level than for the AZ vaccine. At the 25 week (just under 6 month) point after the second dose, the Pfizer vaccine has been found to give around 60% protection against Delta, and only 40% protection against Omicron.

For those who have received booster vaccine doses, the Pfizer vaccine seems to be more effective at maintaining protection. However, the level of protection is still only on a par with Delta, at around 70-75%.



As can be seen above, it is clear that Omicron poses a severe risk to everybody, especially those who are clinically vulnerable. The transmissibility of Omicron is at least as high, and likely higher than, that of Delta, and it is vaccine resistant to some extent. We do not yet know how resistant it is, or how severe the illness it causes is, but more data should emerge on this soon. Existing treatments are less likely to work against it, and new ones are not yet available or proven against it. Regardless of severity, Omicron is going to lead to a rise in cases, hospitalisations and deaths over the Christmas period, regardless of the new ‘Plan B’ restrictions. BuDS strongly advises everyone to avoid crowds or crowded spaces (whether indoor or outdoor), always wear a high-quality mask when out and about near people, and to maintain social distancing wherever possible. Covid-19 is getting more dangerous, and the risk to your health has never been higher.



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