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CT chest differences reveal less severe infection with omicron compared to delta

29th June 2022

CT chest changes are less severe with the omicron COVID-19 variant compared to delta and help explain the better patient outcomes with delta

Computed tomography (CT) chest scan changes after infection with the omicron COVID-19 variant are less severe than those seen with the delta variant and lead to better patient outcomes. This was the conclusion of an analysis of CT chest scans by researchers from Oxford University, UK.

The COVID-19 omicron variant of concern was first identified in South Africa in November 2021 and an analysis in January 2022 suggested a significantly reduced chance of being hospitalised for individuals infected with the omicron variant compared to previous variants of concern. In fact, the authors suggested that this reduction in severity was most likely due due to a degree of protection from prior immunity.

While there is evidence to show that among those who experience a breakthrough COVID-19 infection, examination of CT chest scans indicate a lower level of pneumonia, the study did not provide any information on the infective variants involved. Moreover, a CT chest has become a valuable tool for the detection of both alternative diagnoses and complications of COVID-19, but to date, there is a lack of information on the CT changes induced after infection with different COVID-19 variants.

For the present study, the Oxford team compared the radiological patterns, imaging characteristics and disease severity on initial CT chest angiograms of patients infected with the omicron and delta variants of concern.

They retrospectively collected data on patients hospitalised and with a PCR confirmed positive COVID-19 test, using the S gene target failure as a surrogate for omicron infections. For the CT chest scans, a severity score (CT-SS) was calculated (ranging from 0 to 25, with higher scores reflecting greater severity) and CT imaging features such as bronchial wall thickening were also assessed.

Additional data collected included demographics, co-morbidities, laboratory findings, in-hospital treatments and clinical outcomes. Logistic regression models were created and adjusted for potential confounding variables to identify any differences in outcomes for the two variants.

CT chest changes induced by omicron and delta variants

A total of 106 adult patients with a mean age of 58 years (55% male) were included in the final analysis, of whom, 66 were infected with the delta variant.

Based on the CT chest findings, a higher proportion of scans were categorised as normal in patients with omicron compared to delta (37% vs 15%, omicron vs delta, p = 0.016). Interestingly, only 40% of those infected with omicron compared to 83% of those with delta, displayed the typical signs of pneumonia.

Patients infected with omicron had a lower median CT-SS score compared to those with delta (3.5 vs 11.8). Furthermore, bronchial wall thickening was more common in those with omicron (odds ratio, OR = 2.4, 95% CI 1.01 – 5.92, p = 0.04).

Infection with the delta variant was also associated with a higher odds of more severe infection (OR = 4.6, 95% CI 1.2 – 26, p = 0.01) and critical care admission (OR = 7).

The authors concluded that infection with the omicron variant is associated with fewer and less severe changes on a CT chest compared to the delta variant and led to better patient outcomes.

Tsakok MT et al. Chest CT and Hospital Outcomes in Patients with Omicron Compared with Delta Variant SARS-CoV-2 Infection Radiology 2022

Bivalent Moderna vaccine likely to protect against Omicron sub-variants

26th June 2022

A bivalent Moderna vaccine was found to produce a potent neutralising antibody response against two Omicron sub-variants BA.4 and BA.5

A bivalent Moderna vaccine is able to generate a large neutralising antibody response against two of the Omicron sub-variants, BA.4 and BA.5 and therefore likely to protect against these variants.

Both the BA.4 and BA.5 sub-variants of Omicron were detected in South Africa in January and February 2022, respectively. Moreover, there have recently been concerns raised over these two sub-variants especially after a study published in the New England Journal of Medicine, found that the sub-variants, substantially escaped neutralising antibodies induced by both vaccination and infection.

The results of the study showed that among individuals who had received a third (i.e., booster) dose of BNT162b, compared with the response against the original COVID-19 isolate, the neutralising antibody titre was lower by a factor of 21 against BA.4 or BA.5. In other words, it appears highly likely that even among those who have been fully vaccinated, the BA.4 and BA.5 can lead to re-infection.

The bivalent Moderna vaccine has been studied in a phase 2 and phase 3 trial which has yet to be published. In the study, all participants who had previously received 2 or 3 doses of an approved COVID-19 vaccine were then given mRNA-1273.529, mRNA-1273.214, or mRNA-1273 as the 4th dose.

Bivalent Moderna vaccine and Omicron sub-variants

When considering the COVID booster candidate, mRNA-1273.214, only one month after administration in previously boosted participants, a 50 µg booster dose elicited potent neutralising antibody responses against the Omicron sub-variants BA.4 and BA.5 in all participants.

In fact, mRNA-1273.214 was able to increase the level of neutralising antibody titres against BA.4/BA.5 by 5.4-fold (95% CI 5.0 – 5.9) above baseline in all participants regardless of prior infection and by 6.3-fold (95% CI 5.7 – 6.9) in the subset of seronegative participants.

These results follow on from previous data from early June 2022, in which Moderna found that a booster dose with mRNA-1273.214 increased neutralising geometric mean titres (GMT) against the Omicron variant by approximately 8-fold above baseline levels.

Moreover, a 50 μg booster dose of mRNA-1273.214 was well-tolerated in the 437 study participants and both the safety and reactogenicity profile of mRNA-1273.214 was similar to that of mRNA-1273 when these vaccines were administered as a second booster dose.

Based on these preliminary findings, Moderna is now working hard to complete all the necessary regulatory submissions in the coming weeks requesting to update the composition of the booster vaccine to mRNA-1273.214.

Study shows that BNT162b vaccination reduces risk of Omicron-associated hospitalisation by two-thirds in children aged 5-11 years

22nd April 2022

A study by researchers in the US has concluded that BNT162b vaccination given to children aged 5 to 11 years reduced the risk of Omicron-associated hospitalisation by more than two-thirds but was less effective against hospitalisation among adolescents.

BNT162b2 vaccination in 12 to 15-year-old recipients has been shown to have a favourable safety profile, produce a greater immune response than in young adults and be highly effective against COVID-19. Nevertheless, data on vaccine effectiveness have only been assessed up to 3 months post-vaccination and the available data preceded circulation of the Omicron COVID-19 variant. Furthermore, there are limited data on the effectiveness of vaccines in younger children, although one study has indicated that vaccination against laboratory-confirmed COVID-19-associated hospitalisation among children aged 5-11 years was 74%, and between 14 and 67 days after a second dose, although this estimate had wide confidence interval (–35% to 95%) that included zero.

For the present study, the US team set out to determine the duration of protection from BNT162b vaccination in adolescents during different periods of time in which the Delta and Omicron were the dominant circulating strains. They also examined the protection of the vaccine against hospitalisation in children aged 5 to 18 years of age infected with the Omicron variant.

The team used a case-control, test-negative design to assess BNT162b effectiveness against COVID-19-related hospitalisation and against critical illness. The researchers also included a group of control patients who were in the same age categories and defined as hospitalised individuals who tested negative for COVID-19 and with no recognised symptoms of the virus. The effectiveness of BNT162b vaccination was assessed after 2 to 22 weeks and after longer than 22 weeks.

BNT162b vaccination and COVID-19

Among those hospitalised aged 12 – 18, there were 918 case patients with a median age of 16 years (50% female), of whom 78% had at least one underlying health condition. In addition, there were 267 case patients with a median age of 8 years (43% female) and of whom 82% had at least one underlying health condition.

Overall among the 1185 cases (i.e., 267 and 918), 25% had critical COVID-19, 14 of whom died. In the 12 to 18 group (918 cases), 27% had critical COVID-19 and 13 died. In the 5 – 11 group (267 cases), 16% had critical COVID-19, one of whom died.

The effectiveness of BNT162b vaccination against COVID-19-associated hospitalisation among adolescents was 92% during the Delta period, 2 to 22 weeks after vaccination and 92% between 23 and 44 weeks post-vaccination. However, during the omicron period, vaccine effectiveness was only 40% against COVID-19-associated hospitalisation, 2 to 22 weeks after vaccination and dropped slightly to 38% between 23 and 44 weeks post-vaccination. Nevertheless, during the Omicron period, vaccine effectiveness was 79% against critical COVID-19 but only 20% against non-critical illness.

Among those aged 5 – 11 years of age, vaccine effectiveness against COVID-19-associated hospitalisation was 68% during the Omicron period, a median of 34 days after vaccination.

The authors concluded that vaccination in children aged 5 to 11 years reduced the risk of COVID-19-associated hospitalisation by two-thirds during the Omicron period adding that while vaccination was less effective in adolescents during the omicron period, it was still able to prevent critical illness.

Price AM et al. BNT162b2 Protection against the Omicron Variant in Children and Adolescents N Engl J Med 2022

Large study confirms less severe outcomes after infection with Omicron compared with Delta variant

29th March 2022

A large UK comparative analysis has found that infection with the Omicron COVID-19 variant leads to less severe outcomes than with Delta

Individuals who become infected with the Omicron COVID-19 variant experience less severe outcomes such as hospitalisation and death compared to those with the Delta variant according to the results of a large study by a multi-disciplinary group of UK researchers.

The Omicron COVID-19 variant has produced a surge of infections and been found to be associated with high transmission among household contacts, particularly among those who lived with index patients who were not vaccinated or who did not take measures to reduce the risk of transmission to household contacts.

Nevertheless, despite a higher level of transmissibility, studies have also suggested that the Omicron variant is associated with substantial severity of illness in comparison to the Delta variant.

With an increasing number of individuals now fully vaccinated against COVID-19, the purpose of the present study was to offer a more detailed understanding of the overall impact of both less severe outcomes and greater immunity on rates of hospitalisation and mortality during the Omicron wave.

The UK team obtained individual-level data on confirmed cases of COVID-19 infection in England between November 2021 and 9 January 2022 and linked these to vaccination status, hospital attendance and admission as well as deaths.

During the period of study genomic sequencing was performed for some of the infections which enabled the team to distinguish between the two variants. For the study, a hospital admission was defined as a stay of at least one or more days. The analysis was stratified by age, vaccination status and adjusted for sex, deprivation index and evidence of prior infection.

Omicron caused less severe outcomes

During the period of study there were 4,135,347 confirmed cases of COVID-19, of which 1,526,702 (37%) had information on the infecting variant and consisted of 448,843 Delta and 1,067,859 Omicron cases.

The adjusted hazard ratio (HR) for attendance at hospital, but not necessarily admission, was lower for Omicron than Delta (HR = 0.56, 95% CI 0.54 – 0.58). In addition, compared to Delta, the risk of hospital admission among those infected with Omicron was 59% lower (HR = 0.41, 95% CI 0.39 – 0.43) and the risk of death within 28 days was 69% lower (HR = 0.31, 95% CI 0.26 – 0.37).

When stratified by age, there was no difference between the two variants among those 10 years of age and younger (HR = 1.10, 95% CI 0.85 – 1.42). However, there was a significant difference and reduction among those at least 80 years of age (HR = 0.47, 95% CI 0.40 – 0.56).

For both of the variants, prior infection offered protected against death in those who were vaccinated (HR = 0.47) and unvaccinated (HR = 0.18). Interestingly, among those who were vaccinated, prior infection appeared to offer no additional protection against infection (HR = 0.96, 95% CI 0.88 – 1.04), which was in contrast to those who were unvaccinated but had a previous infection (HR = 0.55, 95% CI 0.48 – 0.63).

The authors concluded that the less severe outcomes observed for Omicron were largely driven by a less severe variant and increased immunity due to vaccination.

Nyberg T et al. Comparative analysis of the risks of hospitalisation and death associated with SARS-CoV-2 omicron (B.1.1.529) and delta (B.1.617.2) variants in England: a cohort study Lancet 2022

Blood cancer patients have lower antibody response to Omicron after third COVID vaccine dose

3rd February 2022

Blood cancer patients who have received a third vaccine dose continue to produce a limited antibody response to the Omicron variant

Patients with blood cancer generate a reduced neutralising antibody response to the Omicron variant even after a third vaccine dose, according to a study by a UK team of researchers.

Patients with cancer who become infected with COVID-19 are known to have a higher mortality risk compared with those without the disease. However, as cancer patients were excluded for the pivotal COVID-19 vaccine trials, there was always some uncertainty over the ability of such patients to mount a sufficient neutralising antibody response to vaccination.

Available data has shown how blood cancer patients such as those with chronic lymphocytic leukaemia, have an impaired antibody response to vaccination. A further problem is that with the emergence of variants of concern which are capable of immune escape, the antibody response might be even worse.

In fact, such fears appear to have been realised with one study reporting that blood cancer patients were more likely to have undetectable neutralising antibodies compared to those with solid cancers against both the wild-type and the Alpha, Beta and Delta COVID-19 variants of concern.

Despite these findings, administration of a third COVID-19 vaccine appears to boost the neutralising antibody response for those with solid tumours but the response remains muted in blood cancer patients. For instance, one study found that following the third dose, only 54% had detectable neutralising antibodies against Delta and 54% against Beta.

For the present study, the researchers focused their attention on the Omicron variant and sought to examine the immune response generated in response to this variant in those with both solid tumours and blood cancers. The team used a live-virus micro-neutralisation assay to evaluate the response to Omicron following three doses of COVID-19 vaccines in participants enrolled in the CAPTURE study, which was a prospective and longitudinal study of patients with cancer.

Blood cancer patients’ response to third vaccine dose

The researchers enrolled 199 patients, 58% of whom had a solid cancer and the remainder a blood cancer, all of whom had received a third COVID-19 vaccine dose. They also included a matched sample before the third dose which included 179 patients (115 with solid cancers and 84 with a blood cancer).

After two COVID-19 vaccine doses among the 100 patients with solid cancers, 37% generated detectable neutralising antibodies against Omicron. In contrast, among 79 patients with a blood cancer, only 19% generated a detectable response to Omicron after two vaccine doses.

With a third vaccine dose, among the 115 patients with a solid cancer, neutralising antibodies to Omicron were detected in 90% of patients. However, for the 84 patients with a blood cancer, after a third vaccine dose, Omicron neutralising antibodies were only detectable in 56% of patients.

Based on these findings, the authors concluded that while a third vaccine dose enabled those with solid cancers to produce a robust neutralising antibody response to Omicron, only half of those with a blood cancer were able to mount a sufficient response, highlighting the need for a possible fourth dose in this patient cohort.

Fendler A et al. Omicron neutralising antibodies after third COVID-19 vaccine dose in patients with cancer Lancet 2022

Omicron Covid variant remains infective for 21 hours on human skin

27th January 2022

The Omicron Covid variant has been shown to maintain infectivity on human skin for at least 21 hours and nearly 200 hours on plastic surfaces

The Omicron Covid variant is environmentally stable and can survive for at least 21 hours on human skin and 193 hours on plastic surfaces. This was the finding by a team from the Department of Infectious Diseases, Kyoto Prefectural University of Medicine, Kyoto, Japan.

The Omicron variant has numerous mutations which have likely led to enhanced transmissibility. One potential factor associated with greater transmissibility is the spread from contact with human skin. The stability of the original COVID-19 variant on human skin has been found to be 9 hours which is considerably longer than the human influenza A virus. While some evidence has revealed how both the B.1.1.7 and B.1.351 covid variants had similar levels of surface stability, there is a lack of comparative data for all of the currently identified variants.

For the present study, the Japanese team examined the environmental stability of several circulating variants of concern, including the Omicron variant and compared this to the original Wuhan strain. They also sought to determine the disinfectant efficacy against the different strains. The stability was tested on human skin samples collected from forensic autopsy specimens approximately one day after death. The stability of the variants was also evaluated on plastic (polystyrene plates).

In all experiments, samples were applied to the surface of either skin or plastic and incubated and the amount of remaining viable virus determined. They defined the survival time as the time until virus could no longer be detected and each experiment was conducted three times.

Omicron covid variant survival

When tested on plastic surfaces, the Wuhan strain survived for 56 hours (95% CI 39 – 76.7 hours) whereas the omicron variant survived for 193.5 hours (95% CI 153.1 – 236.2 hours). For comparative purposes, the delta variant survived a similar length of time (114 hours).

When tested on human skin, the Wuhan strain survived for 8.6 hours (95% CI 6.5 – 10.9 hours) whereas the omicron variant lasted 21.1 hours (95% CI 15.8 – 27.6 hours). The Delta variant also survived longer than the Wuhan strain, lasting 16.8 hours (95% CI 13.1 – 21.1 hours).

In the presence of a 40% ethanol solution, the omicron covid variant was completely inactivated within 15 seconds. Furthermore, on human skin, all strains were completely inactivated after 15 seconds with exposure to 35% ethanol.

Discussing their findings, the authors noted how the Omicron variant appeared to survive on plastic surfaces for much longer than the Wuhan strain and that this enhanced environmental stability could be an important factor with the increased level of transmissibility of the variant. They added that since the variant is completely inactivated after 15 seconds, this highlighted the importance of continued infection control measures such as hand hygiene.


Hirose R et al. Differences in environmental stability among SARS-CoV-2 variants of concern: Omicron has higher stability BioRxiv 2022

Study shows third COVID-19 vaccine dose 37% effective against Omicron after 7 days

5th January 2022

A third COVID-19 vaccine dose appears to offer only limited protection against Omicron compared with infection with the Delta variant

A third COVID-19 vaccine dose appears, in practice, to be unlikely to offer much protection against the Omicron compared with the Delta variant. This was the finding of a preprint from a large Canadian study by a team led by Public Health Ontario, Toronto, Canada.

The Omicron COVID-19 variant was first reported to the World Health Organization (WHO) from South Africa on 24 November 2021 and the WHO has since designed it as a variant of concern due to an increased transmissible nature and the potential for immune evasion.

Moreover, early data suggests that while a third COVID-19 vaccine dose offers higher protection against Omicron, the authors added that ‘even with three vaccine doses, neutralisation against the omicron variant was lower (by a factor of 4) than that against the delta variant.’

In trying to provide some much needed data on the real-world effectiveness of vaccine effectiveness (VE) against the Omicron or Delta variant, the Canadian team examined individuals 18 years and over, with a positive PCR test result between November 2021 and December 2021, excluding long-term residents and those who had received only a single COVID-19 vaccine dose or a second dose less than 7 days prior to testing.

The researchers identified confirmed cases of infection, irrespective of symptoms or severity using provincial reportable data. Any positive samples with an S-gene Target failure (SGTF), were considered to be due to infection with Omicron since this failure is absent in those with the Delta variant.

They compared infection rates (compared to those who were unvaccinated and which served as the reference group) for individuals with either two or a third COVID-19 vaccine dose.


The team identified 3,442 Omicron positive, 9,201 Delta positive and 471,545 negative controls. Omicron infected individuals were generally younger, mean age 34.8 years (49.2% male) compared to 43.7 years (same gender proportion) for Delta infections.

After two doses of a COVID-19 vaccine, VE efficacy against Delta was 71% (95% CI 66 – 75%) > 240 days after the second dose but this figure increased to 93% (95% CI 92 – 94%) > 7 days after a third dose.

In contrast, two vaccine doses was not protective against Omicron at any point in time and the VE was – 38% (95% CI – 61 to – 18%) after the second dose.

However, VE against Omicron was 37% (95% CI 19 – 50%) > 7 days after a third COVID-19 vaccine and these findings were consistent for all combinations of the vaccines used.

The authors discussed how their findings have potentially important implications in so far as proof of vaccination (defined by at least two doses) should no longer be considered as fully vaccinated.

They concluded that protection from three vaccine doses offers some protection against the variant but the effectiveness against severe disease remains uncertain.


Buchan SA et al. Effectiveness of COVID-19 vaccines against Omicron or Delta infection MedRxiv 2021.

Omicron infection causes fewer hospitalisations and severe disease compared with Delta variant

24th December 2021

Omicron infection appears to be associated with a lower risk of hospitalisation and less severe disease than the Delta COVID-19 variant, according to a recent study

According to a preprint study by researchers from the Centre for Respiratory Diseases and Meningitis, Johannesburg, South Africa, Omicron infections appear to be associated with reduced risk of hospitalisation and after admission, less severe disease than the Delta variant.

While the Omicron COVID-19 variant was only identified in November 2021, there has been a flurry of research activity directed at trying to understand its transmissibility, the level of disease severity and effect on healthcare services. While initial laboratory studies have indicated that the variant can escape neutralisation by antibodies generated in fully vaccinated and boosted sera samples, these studies cannot foretell the clinical impact of the variant.

The South African researchers undertook a data linkage study of COVID-19 infections, case data and genomic information to establish whether an Omicron infection was associated with higher rates of hospitalisation and more severe disease among those who were hospitalised in comparison to the Delta COVID-19 variant. Although whole genome sequencing was not used, they utilised the presence of a S Gene Target Failure (SGTF), which serves as a proxy for Omicron and samples were examined between 1st October 2021 and 6th December 2021. Positive infections were therefore classified as either an SGTF or non-SGTF. The severity of an Omicron infection was assessed by comparison of SGTF and non-SGTF infections and to infections known to be caused by the Delta variant and regression models created and adjusted for several factors known to be associated with hospitalisation (e.g., age, sex, co-morbidities).


During the period of study there were 161,328 COVID-19 cases recorded and the proportion of SGTFs increased from 3% (early October 2021) to 98% (early December).

A total of 11,495 hospital admissions occurred with 2.5% due to an SGTF compared to 12.8% with a non-SGTF (p < 0.001). Multivariate analysis revealed that individuals with a SGTF had a lower odds of hospitalisation (adjusted odds ratio, aOR = 0.2, 95% CI 0.1 – 0.3, p < 0.001). In addition, once hospitalised, the odds of having severe disease were also reduced in those with SGTF although there was uncertainty over this estimate given the wide confidence intervals (aOR = 0.70, 95% CI 0.30 – 1.40).

Finally, the researchers found that compared to infection with the Delta variant, those with an SGTF had a significantly lower risk of severe disease (aOR = 0.30, 95% CI 0.20 – 0.50, p < 0.001).

The authors suggested that these data suggested that an Omicron infection was probably less severe than other variants such as Delta but recognised that this reduced severity might be accounted for by the higher levels of population immunity due to either natural infection and/or vaccination.

These results are broadly similar to those of a second recently published preprint from Scotland which found a nearly 70% reduced risk of hospitalisation (expected ratio = 0.32, 95% CI 0.19 – 0.52) for those with an Omicron infection. The study also found that giving a third or booster dose was associated with a 57% reduced risk of symptomatic infection.

Although both studies are preliminary, they do suggest the possibility that infection with the new variant is potentially less severe than other forms.


Wolter N et al. Early assessment of the clinical severity of the SARS-CoV-2 Omicron variant in South Africa. MedRxiv 2021

Third booster sera samples have reduced neutralisation against Omicron COVID-19 variant

22nd December 2021

Third booster sera samples have been found to produce a four- six-fold decrease in neutralisation when tested against the Omicron variant

In a laboratory-based study, third booster sera samples from patients have been shown to produce a four to six-fold reduction in neutralisation against the Omicron COVID-19 variant. This was the finding of a preprint study by researchers from the Aaron Diamond AIDS Research Center, New York, US.

The Omicron COVID-19 variant (B.1.1.529) was first identified in southern Africa and appears to have a high level of transmissibility and will likely cause outbreaks across the globe. A concern with this particular variant is that it contains more than 30 mutations,15 of which are present in the receptor-binding domain region which is the target for neutralising antibodies produced in response to vaccination. It is therefore possible that the Omicron might lead to an increased level of infection despite vaccination although current opinion is that this could be mitigated by a third booster sera sample.

In the absence of clinical data, the US team sought to better understand the extent to which the Omicron variant is able to evade antibody neutralisation, by testing the activity of serum collected from a number of different patient samples. Initially the team created an Omicron pseudovirus and tested this against 10 sera samples collected from the Spring of 2020, which were likely to have been infected with the wild-type (original) COVID-19 virus. While there was a robust response to the wild-type, there was a greater than 32-fold reduction against Omicron and only two samples produced antibody titres above the limit of detection.

Vaccinated samples

The team then turned their attention to both fully vaccinated and third booster sera (TBS) samples. For the two mRNA-based vaccines, BNT162b2 and mRNA-1273, there was a >21-fold decrease in ID50 and > 8.6-fold decrease in boosted sera samples. For the other vaccines, Ad26.COV2.S and ChAdOx1, all samples produced antibody titres below the limit of detection apart from two samples for which the individual had a history of a prior infection.

Using 15 third booster sera samples obtained from BNT162b2 (13) and mRNA-1273, the researchers discovered that although each of these third booster sera produced antibody titres above the limit, there was a mean 6.5-fold drop compared to the wild-type.

Using authenticated Omicron isolates and samples from BNT162b2 and mRNA-1273, there was a greater than 6-fold drop in titres for fully vaccinated and a greater than 4.1-fold drop for boosted samples.

Finally, testing sera with monoclonal antibodies, the researchers found that all four combinations of monoclonal antibodies in clinical use lost substantial activity against Omicron.

Although this was a laboratory-based study and might not be replicated in clinical practice, the authors believed that COVID-19 is potentially only a mutation or two away from being resistant to current antibodies and that it was important to devise strategies that anticipate the evolutional direction of the virus and that future work should focus on the development of agents targeting conserved parts of the virus.


Liu L et al. Striking Antibody Evasion Manifested by the Omicron Variant of SARS-CoV-2 BioRxiv 2021

Discovery Health study finds two doses of BNT162b2 70% effective against hospital admission during Omicron variant outbreak

16th December 2021

Discovery Health data suggest that two doses of BNT162b2 provide 70% protection against hospitalisation during the Omicron COVID-19 outbreak

Discovery Health, a private health insurance administrator from South Africa, has released real-world data on the Omicron outbreak in South Africa, indicating that among those with at least two doses of BNT162b2, there was a 70% reduced risk of severe complications of COVID-19 that required hospitalisation.

Although a press release rather than a full, peer-reviewed study, the available data offers some insight of the first three weeks of the Omicron-driven wave in South Africa, and, as the release emphasises, the results should be considered preliminary and could change as the wave develops further.

The analysis provided in the press release includes more than 211,000 COVID-19 test results, 41% from adults who had already received two doses of BNT162b2. Among these 211,000 test results, approximately 78,000 were attributed to the Omicron variant and in those who were fully vaccinated with BNT162b2, the vaccine offered only 33% protection against infection (compared to unvaccinated individuals). However, the Discovery Health data showed that fully vaccinated individuals had a 70% protection against hospital admission during the initial wave of the Omicron variant and this protection was consistent across a range of chronic illnesses including hypertension, hypercholesterolaemia and other cardiovascular diseases. In addition, protection was maintained across all ages but was slightly lower among older patients. For example, in patients aged between 60 to 69, protection reduced to 67% and 60% for those aged 70 to 79 years.

A more worrying concern from the Discovery Health analysis was how overall, the Omicron variant appeared to be much more transmissible, with a 40% higher risk of re-infection. In those who had been infected during the second South African wave (with the beta variant), the risk was 60% higher and higher still at 73%, in those infected during the initial COVID-19 wave in the country.

With respect to children, the press release states that children under 18 years of age had a 20% higher risk of admission to hospital for COVID-19-related complications if infected with Omicron although overall, children were 51% less likely to test positive for the virus during the Omicron period.

On a more positive note, the Discovery Health analysis does indicate that COVID-19 infection caused by the Omicron variant is generally mild disease adding that ‘this lesser severity could, however, be confounded by the high seroprevalence levels of SARS CoV-2 antibodies in the general South African population, especially following an extensive Delta wave of infections.’

The current press release is both encouraging and worrying and until further data becomes available, the impact of the Omicron variant remains to be seen.