Omicron 3 times more likely to transmit in households than Delta

Omicron-infected Brits are THREE TIMES more likely to give virus to people they live with than with Delta – as data shows 6% of all UK’s confirmed cases are reinfections

  • People with Omicron infected a member of their household in 18% of cases 
  • UKHSA said 305 of the 5,153 strain cases up to December 12 were reinfections 
  • Group with the highest infections of the variant was women in their 20s 

Omicron-infected Brits are three times as likely to spread Covid to someone they live with as those with Delta, Government scientists revealed today.

Household transmission is already the main driver of the pandemic, with up to 43 per cent of all infection believed to be caused by family members in the home.  

The UK Health Security Agency said the super mutant strain, which today officially became dominant in the UK, has an even bigger ‘transmission advantage’.

Of the 777 confirmed Omicron cases up to December 12 in England, some 140 household members (18 per cent) would be infected by the strain, the UKHSA said. 

The report also showed six per cent of all confirmed cases of the variant in the UK are reinfections, with Government modelling estimating the strain is five-and-a-half times more likely to reinfect than Delta.

Some 305 of the 5,153 people with a confirmed or probable case of Omicron recorded between November 1 and December 11 were connected to a previous confirmed infection and were at least 90 days from previously testing positive.

Meanwhile, it showed the group with the highest infections of the strain as of December 12 in England was women in their 20s.  

A UK Health Security Agency report showed six per cent of all confirmed cases of the variant in the UK are reinfections. Of 5,153 people with a confirmed or probable case of Omicron recorded between November 1 and December 11, 305 were connected to a previous confirmed infection and were at least 90 days from previously testing positive. Graph shows: The weekly rate of possible reinfections in England (blue line)

Meanwhile it showed the group with the highest infections of the strain as of December 12 in England was women in their 20s

Graph shows: Confirmed Omicron cases by travel status in England up to December 12. Most cases in the country were initially from abroad (green) although this was quickly overtaken by domestic cases (pink), with the majority now in people with unknown traveller status (purple)

Graph shows: Omicron cases by region in England up to December 12. London (light blue) makes up the majority of all confirmed infections of the variant

Women made up 789 of all infections, 50 per cent more than men in the age group (523) and more than double any other group other than women (419) and men (418) in their 30s.

The variant has caused cases to spiral across the UK, with infections now also rising in those in their 60s in the Omicron epicentre London. 

Lateral flow tests used in the UK identify Omicron with just as much accuracy as previous strains, UK Government scientists insisted today.

Experts said they hope the results will allay concerns the devices are less sensitive to the mutant strain. 

As cases have soared in recent days, scores of Britons have complained about testing negative on lateral flows, only to be told they are positive by a PCR.

The UK Health Security Agency (UKHSA) used the five lateral flow testing brands dished out by the NHS on samples from patients infected with Omicron. 

All of the tests showed a positive result for each patient, even when their sample was diluted, showing the devices have ‘a comparable sensitivity to that observed for previous strains’ of Covid, the UKHSA said.

However, it is monitoring how well the tests perform in the real world to ensure their sensitivity is not ‘significantly reduced’ when people swab themselves.

The tests, which can tell if someone is infected in as little as 15 minutes, report positive results by detecting the virus’s nucleocapsid protein. 

But this part of Omicron’s cell has four mutations, which raised concerns that the test could be less effective. 

But Dr Jenny Harries, chief executive at the UKHSA, said the laboratory results are ‘very encouraging’ and urged people to use the tests before mixing with others to limit the spread of the virus.

The free tests are a key part of No10’s Plan B strategy, with vaccinated close contacts of positive cases told to use them daily for a week instead of isolating. 

Unvaccinated people must show proof of having a negative result to enter football stadiums.

Wales today announced new restrictions, with Mark Drakeford announcing a crackdown on social gatherings and closures of nightclubs from Boxing Day, while Scots are being urged to limit mixing to three households and people in England are advised to ‘prioritise’ social events.

Gloomy modelling from ‘Professor Lockdown’ Neil Ferguson today suggested there could be 5,000 Covid deaths a day this winter without more restrictions.  

The UKHSA studied 116,186 Covid cases from November 15 to December 6, of which 115,407 were Delta and 777 were Omicron.

Overall, 18 per cent of Omicron cases caused another infection in people living in the same household, compared to 10 per cent of Delta cases.

Statistical modelling determined the risk of spreading the strain to another household member is 2.9 times higher for Omicron than it was for Delta.

The data was adjusted for age, sex, race, geography, infection date, number of household contacts and vaccination status.

But the experts said more data is necessary to draw stronger conclusions, adding they would repeat the analysis in future once more cases of the variant have been picked up. 

The report said: ‘A multivariable logistic regression model found the adjusted odds ratio for household transmission from an Omicron index case was 2.9 compared to Delta index cases. 

‘These preliminary findings suggest that the Omicron variant has a transmission advantage compared to Delta. 

‘However, this analysis may be affected by increased ascertainment of Omicron cases. The analysis will be iterated to improve precision.’

The report also suggest Omicron is causing ‘an increase in overall reinfection rates, alongside an increase in first infections’.

The ages of the cases linked with a previous infection ranged from six to 68 years old, while there were four people for whom Omicron was their third episode of infection. 

And it found that lateral flow (LFD) tests are as likely to detect Omicron as other variants of coronavirus. 

Dr Jenny Harries, HSA’s chief executive, said: ‘Our data shows that LFD tests are similarly able to detect Covid-19 in individuals who have been exposed to Omicron as in those exposed to previous variants. This is very encouraging.

‘As we all work to limit the high levels of transmission of this variant over the Christmas period, we are urging people to test regularly, particularly before attending social gatherings.

‘As always, the booster vaccine remains the best protection against infection. Please come forward to receive your booster as soon as possible.’

Meanwhile, a separate study by Imperial College London released today showed the risk of reinfection with Omicron is 5.4 times greater than that of the Delta variant.

This suggests the protection against reinfection by Omicron from past infection may be as low as 19 per cent.

The study also found no evidence of Omicron having lower severity than Delta, but data on hospital admission was very low at the time of the study.

According to the data, boosters are vital in controlling Omicron, but they may lose some effectiveness over time.

Researchers estimated the proportion of Omicron among all Covid cases between November 29 and December 11 was doubling every two  days up to December 11.

Based on this they also estimate the reproduction number (R) of Omicron was above 3, over the period studied.

 

Professor Neil Ferguson from Imperial College London said: ‘This study provides further evidence of the very substantial extent to which Omicron can evade prior immunity, given by both infection or vaccination.

‘This level of immune evasion means that Omicron poses a major, imminent threat to public health.’

There is significantly increased risk of developing a symptomatic Omicron case compared with Delta for those who were two or more weeks past their second vaccine dose, and two or more weeks past their booster dose (for AstraZeneca and Pfizer vaccines), the report found.

Depending on vaccine effectiveness estimates against symptomatic infection from the Delta variant, this translates into vaccine effectiveness estimates against symptomatic Omicron infection of between zero per cent and 20 per cent after two doses, and between 55 per cent and 80 per cent after a booster dose.

The scientists used data from the UKHSA and NHS for all PCR-confirmed Covid cases in England who had taken a test between November 29 and December 11 this year.

Professor Azra Ghani, from Imperial College London, said: ‘Given the rapid spread of the Omicron variant to date, it is now highly likely that this will replace the circulating Delta variant globally in the coming weeks.

‘Emerging immunogenicity data clearly point to substantial reductions in neutralising antibodies, whilst preliminary vaccine efficacy estimates demonstrate a substantial reduction in protection from mild disease.

‘Our estimates suggest that this is likely to translate into small but important reductions in efficacy against severe disease and death.

‘One remaining uncertainty is how severe the disease caused by the Omicron variant is compared to disease caused by previous variants.’

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