Since the first cases of Omicron were reported in the UK just over a month ago it has spread rapidly across the UK, fuelling a surge of infections. But scientists have also been working at speed. Here is an overview of the expanding scientific knowledge of Omicron.
Spread
Soon after the variant was first detected in southern Africa, it became apparent Omicron was highly transmissible. According to the UK Health Security Agency (UKHSA), Omicron is displaying a growth advantage over the Delta variant in the UK.
“Although we now have high confidence in a substantial component of immune evasion, the very high growth rate and laboratory findings suggest that an increase in transmissibility may also be contributing,” the latest risk assessment for Omicron notes.
The growth of Omicron has been reflected not only in record confirmed case numbers but also in random swab tests taken in the community. According to the latest estimates from the Office for National Statistics, about one in 25 people in England – equating to 2,024,700 – had Covid in the week ending 23 December.
Vaccines
A number of studies have shown that Omicron has a substantial ability to evade immune responses.
According the latest data released on Friday by the UKHSA, two doses of the Oxford/AstraZeneca Covid jabs offer little protection against symptomatic infection, while 20 weeks after a second dose of the Pfizer/BioNTech or Moderna jabs, protection against Omicron is only about 10%.
However booster vaccinations have been found to ramp up this protection to about 65-75% two to four weeks after the jab, falling to about 40-50% protection from 10 or more weeks after the booster.
Data from the insurer Discovery Health and the South African Medical Research Council has suggested protection against severe complications after two jabs was about 70% for Omicron, compared with 90-95% for Delta.
But research from Imperial College London has suggested vaccine effectiveness against hospitalisation 60 days after a booster is between 80% and 86% against Omicron, depending on how fast booster protection wanes.
Such findings chime with the latest UKHSA data suggesting 88% vaccine effectiveness against hospitalisation two weeks after a booster dose. The NHS announced on Friday that more than three-quarters of adults in England had received their booster.
Immune response
Some experts have suggested that high levels of protection against severe disease may, in part, be down to the action of different components of the immune system. While the mutations in Omicron mean it has a high capacity to escape neutralising antibodies, research has shown it is less able to dodge the body’s T-cells.
However, Prof Danny Altmann, an immunologist at Imperial College London, notes questions remain. “If Omicron has thrived by evading the most potent protection through [neutralising antibodies], it’s unsurprising that the different and numerous T-cell targets are intact, but [we] still lack proof this buys you any protection,” he said.
Severe disease
Recent research in the UK has backed up early suggestions that Omicron may cause less severe disease than Delta, even for those who are unvaccinated and have not previously been infected. According to the latest figures from the UKHSA, overall, people with Omicron are estimated to be about half as likely to go to A&E or be admitted to hospital compared with those with Delta, while the risk of hospital admission alone is approximately a third of that for Delta.
The data also reveals the importance of Covid jabs, noting there is an 81% reduction in the risk of hospitalisation after three doses compared to unvaccinated Omicron cases.
Healthcare
As experts have pointed out, even if only a small proportion of a very large number of infected people end up in hospital, that is still a large number. And both hospital admissions and the number of Covid patients in hospital are rising.
Modelling released by researchers at the University of Warwick on Thursday, yet to be peer-reviewed, suggests that even if Omicron has 50% severity compared with the Delta variant, there could be peaks in the region of 1.4m daily infections, about 9,300-21,3000 daily hospital admissions and 1,800-4,770 deaths a day in January in England. These projections assume England remains under plan B measures only, there is a rapid rollout of booster vaccinations and an efficacy against severe disease with Omicron of 85% after boosting, although experts have cautioned they are based on data from 17 December, meaning some potential scenarios modelled in the work may since have changed.
The team also note that shouldthe level of booster protection be higher, the number of individuals requiring hospital admissions would be lower. There are also other uncertainties that could affect the size of the peaks, including whether Omicron has the same generation time as Delta.
Prof Christina Pagel, the director of UCL’s Clinical Operational Research Unit, said that even under the team’s optimistic scenarios, hospital admissions are likely to be higher than last January under current plan B measures.
“One of the most worrying aspects of their modelling is that time to prevent these hospital pressures was last week or, latest, Boxing Day. If true, this means huge new pressures on the NHS within weeks,” she said.