The latest variant technical briefing suggests that Omicron continues to grow rapidly in all regions of England as measured by confirmed cases and S gene target failure (SGTF). None of the cases to date is known to have been hospitalised or died.

Studies of contacts show that Omicron is transmitting more effectively than Delta. The UK Health Security Agency (UKHSA) estimates that if Omicron continues to grow at the present rate, the variant will become the dominant strain, accounting for more than 50% of all COVID-19 infections in the UK by mid-December. It is projected that if current trends continue unchanged, the UK will exceed one million infections by the end of this month.

The technical briefing also includes early analysis of vaccine effectiveness against the Omicron variant compared to Delta.

The analysis looked at 581 people with confirmed Omicron. It showed that the AstraZeneca and Pfizer-BioNTech vaccines provided much lower levels of protection against symptomatic infection compared to the protection that they provide against Delta. However, the preliminary data showed effectiveness against the new variant appears to increase considerably in the early period after a booster dose, providing around 70% to 75% protection against symptomatic infection.

The analysis included very small numbers of cases as only a few people in the UK currently have this variant, meaning this data should be interpreted with caution until more cases have been studied. Due to the early nature of the findings, all estimates are subject to significant uncertainty and are subject to change. The early observations for 2 doses of AstraZeneca  are particularly likely to be unreliable as they are based on small numbers and are likely to reflect an older population and a population with more co-morbidities than those given the Pfizer vaccine.

There are differences in the populations that have received different vaccines. AstraZeneca was the main vaccine used early in the programme in care homes and among those in clinical risk groups. These groups have been prioritised for booster doses since the start of the rollout in September to increase their protection. The percentage of people to have received a booster dose will also already be higher in older age groups and those with underlying health conditions due to prioritisation of the rollout so far.

Vaccine effectiveness against severe disease from Omicron is not yet known but is expected to be significantly higher than protection against symptomatic disease. Data on this won’t be available for several weeks.

It is vital that everyone over the age of 40 who is eligible for a booster jab comes forward as soon as possible to get increased protection against this new variant. Those aged 18 to 39 should wait to be called.

Dr Mary Ramsay, Head of Immunisation at UKHSA, said:

These early estimates should be treated with caution but they indicate that a few months after the second jab, there is a greater risk of catching the Omicron variant compared to Delta strain.

The data suggests this risk is significantly reduced following a booster vaccine, so I urge everyone to take up their booster when eligible. We expect the vaccines to show higher protection against the serious complications of COVID-19, so if you haven’t yet had your first 2 doses please book an appointment straight away.

Working from home where possible, consistently wearing masks in crowded or enclosed spaces, washing your hands regularly and isolating and getting tested if you feel unwell are also vitally important in reducing the impact of COVID-19 this winter.

UKHSA has also published a breakdown of confirmed Omicron cases and SGTF cases by local authority. The most affected local authorities are West Northamptonshire, where there are 49 confirmed cases and 68 SGTF, and Manchester, where there are 7 confirmed cases and 61 SGTF.

Evidence continues to show that Omicron is transmitting more rapidly than the dominant Delta variant. Studies of households and contacts have found that there is a higher risk of transmission to contacts from an Omicron case, when compared to Delta.

Dr Jenny Harries, UKHSA Chief Executive, said:

Once again, we urge everyone who is able to get a booster jab to come forward and do so. It is the best defence we have against this highly transmissible new variant.

It is also absolutely critical that we all do what we can to reduce transmission in the community so that we have time to administer as many booster doses as possible. Please make sure you follow all the available guidance. Work from home if you are able to, wear a mask indoors around other people, and ventilate indoor spaces well.

Sajid Javid, Secretary of State for Health and Social Care, said:

Today’s new data shows how important booster jabs are to protect us against this variant.

They are our best defence and we have turbocharged our rollout programme inviting 7 million more people over the age of 40 to get their booster jab so even more people get protection from this disease. I urge you to come forward as soon as you’re eligible to help keep yourself and your loved ones safe.”