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expert reaction to UKHSA omicron variant technical briefing, including information on growth and dominance and data on vaccine protection against mild symptomatic disease from Omicron

The UK Health Security Agency (UKHSA) has published the latest technical briefing looking at SARS-CoV-2 variants of concern and variants under investigation in England.


Dr Clive Dix, former Chair of the UK Vaccine Taskforce, said:

“UKHSA data is early but encouraging and gives confidence that omicron is less virulent (low numbers but no hospitalisations).  All data is trending toward Omicron taking over from Delta with less severe consequences so good news.  U.K. elderly and vulnerable being boosted means U.K. will be ok.”


Prof Paul Hunter, Professor in Medicine, UEA, said:

“Today’s technical briefing from UK HSA summarises what is currently known about omicron in the UK.  Although it is still early days here so that this information is subject to change, especially because of small numbers so far estimates have wide confidence intervals.  Key points include:

“1. Omicron is indeed very infectious and seems to be spreading more rapidly in the UK than in South Africa.  In South Africa the latest R estimate is about 2.2.  For the UK the estimate is 3.7 which is doubling every 2 to 3 days.  I would add that early estimates of R in an epidemic tend to decline over a few weeks so this rate may not be maintained for very long.  But even so an R value in this region would mean that even very strict controls like we have earlier this year may not be sufficient to bring R to below 1.0 and reverse the increase.

“2. The results from household studies suggest transmission of omicron between people who live in the same household is about 3.2 times greater than for delta as would be expected from the above R estimate.

“3. Although transmission in non-household settings is still greater for omicron than for delta, the elevated risk of transmission for omicron compared to delta may be less marked for non-household contracts than for household contracts, but confidence intervals are very wide so shouldn’t read too much into that at present.

“4. The effectiveness of two doses of vaccine against omicron is poor.  A primary course of Pfizer gives only about 35% protection against symptomatic illness from 25 weeks after second dose and AstraZeneca hardly any, though confidence intervals are wide due to small numbers.  But a booster after either primary course gives protection against symptomatic infection in the 70 to 80% range – very reassuring especially as we have done pretty well at rolling out booster to our more vulnerable people.  But it is too early to estimate impact on severe disease, though with this data I think we can realistically expect booster doses to give very good protection against severe disease, possibly in the 90% range.

“5. Following similar reports from South Africa, omicron is far more likely to cause reinfections (an infection is someone who has a history of having had covid previously) by about 5 fold.

“Overall this data confirms the much greater transmissibility of omicron but we have increasing evidence that the booster dose will go a long way to reduce the burden of severe disease over coming weeks.  Despite my suggestion even strict lockdown may not be sufficient to reverse the current growth in omicron, I do not think this mean we should go to a strict lockdown.  If the spread of omicron is inevitable the most important things we can do is ensure continuing rollout of booster and targeted rapid distribution of antivirals to vulnerable individuals early after diagnosis.”


Dr Peter English, Retired Consultant in Communicable Disease Control, Former Editor of Vaccines in Practice, past Chair of the BMA Public Health Medicine Committee, said:

“These are robust data, cautiously expressed, as is appropriate given that the data are limited, and that we will need time for the effects of the new variant to become apparent, and to collect and analyse the data.

“There is already clear evidence that this variant is highly transmissible.  Exactly how transmissible will take longer to ascertain; but it is clearly considerably more transmissible than previous variants, including delta.  There is evidence for this from a number of different sources and ways of measuring transmission, increasing the robustness of the finding.

“There is already evidence that existing vaccines are likely to be less effective against this variant.  Laboratory evidence shows that much higher levels of vaccine-induced antibodies are required to neutralise the virus; and there is now also some evidence of reduced vaccine effectiveness against symptomatic disease, although effectiveness is largely restored after three (as opposed to two) doses of vaccine.  Given the huge additional benefits from the third dose for the delta variant, this supports the conclusion that the normal primary vaccination course should comprise three doses of vaccine, not two.

“As the report carefully points out, however, we do not yet have sufficient data to estimate vaccine effectiveness against severe disease (hospital admission, critical care (ICU) admission, and death) caused by this variant: “It will be a few weeks before effectiveness against severe disease with Omicron can be estimated, however based on this experience, this is likely to be substantially higher than the estimates against symptomatic disease.”  The “a few weeks” statement is partly because hospital admission is generally required about ten days after symptom onset, and deaths about three weeks after symptom onset.  The “likely to be substantially higher” statement relates in part to the fact that vaccines are more effective against more severe forms of disease; but also because neutralising antibodies (which we know are reduced against omicron) are required to prevent infection; but a wider immune response, including the cellular immune system and T-cells, is involved in fighting infection and preventing severe disease.  We know that the cellular (T-cell) response is broader than the antibody response, and likely to be more effective against variants than the antibody response.”


Dr Julian Tang, Honorary Associate Professor/Clinical Virologist, Respiratory Sciences, University of Leicester, said:

“Qualitatively – the message on controlling the spread of omicron is similar to delta – get vaccinated and/or boosted, wear masks in indoor crowded areas and public transport, avoid too much social contact if possible, open windows to enhance ventilation if sharing airspace with strangers, etc.

“Quantitatively – to reduce the impending spread of omicron, we just need to do this faster with higher compliance, to reduce any potential future burden on the NHS – if omicron is of comparable clinical severity to delta.

“The number and position of the S gene mutations in omicron do not make its vaccine escape capabilities very surprising – but they will still likely offer protection against severe disease and death.

“However, I am hoping that this will be balanced by a milder and more typical flu-like illness clinical profile.

“Time will tell.”


Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“Few expected vaccines to prevent against infection, or even mild disease – at least not for the mid- to long-term.  What is important is to understand how the vaccines, especially after the booster dose, protect from serious disease.  As the report points out, you can only get that information from real life experience.  Yes, the amount of antibody killing measured in the lab is lower, but we still don’t understand what that means.  Importantly the booster reinstates much of that killing effect, and we also have T cells to throw into the mix.

“It’s right to be cautious, but it would be wrong to spread panic.  We can all do our bit by being careful, and most of all, by getting vaccinated.”



All our previous output on this subject can be seen at this weblink:



Declared interests

Dr Peter English: “Dr English is on the editorial board of Vaccines Today: an unpaid, voluntary, position.  While he is also a member of the BMA’s Public Health Medicine Committee (and its chair until Oct 2020), this comment is made in a personal capacity.  Dr English sometimes receives honoraria for acting as a consultant to various vaccine manufacturers, most recently to Seqirus.”

Prof Jonathan Ball: “Receipt of funding to develop next generation vaccines.”

None others received.

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