As the Omicron variant makes its way through the population of the UK, the Chief Medical Officer’s warning that we don’t know all that much about the variant, but ‘all the things we do know are bad’ was not what anyone wanted to hear this week. Unfortunately, Chris Whitty is right. The Omicron variant’s assault on the UK has been like a blitzkrieg so far, and it has left a trail of shock and confusion in its wake. It is no wonder that Sage have advised this week that more restrictions may now be needed to prevent a rapid rise in hospitalisations.

There is still a lot we don’t know about Omicron, but we have been able to build up a partial picture of the variant. From the outset, scientists were able make educated guesses about how Omicron would behave based on its mutations. One of these guesses was that the wall of immunity built up by vaccines and infections would be less effective against Omicron than Delta. The concern was that Omicron would reduce the vaccine’s effectiveness enough to lead to many more hospital admissions and deaths.

As things stand, all the data we have on vaccine efficacy against Omicron is from laboratory studies which test how effectively blood samples (taken from people at different stages of the vaccine programme) neutralise the ability of the virus to infect cells. As expected, according to this data, vaccine efficacy is reduced against Omicron, but not entirely.

Unfortunately, that’s not the conclusive proof we need to completely understand Omicron. Only when enough infections occur in people in different stages of the vaccine programme will we truly know how effective different vaccines are and for how long their protection lasts. We’re only likely to start to get that information in the next few weeks.

Another concern is that Omicron is more transmissible than variants we’ve seen before. Strictly speaking, what we’re seeing is Omicron’s growth advantage over Delta and it’s not yet clear whether that is due to it evading people’s immunity or because Omicron genuinely is able to jump from person to person more easily. Early laboratory data suggests that the Omicron variant may be more efficient at cell entry and replication in people’s lungs, but there’s no clear epidemiological evidence yet of a transmissibility advantage.

To the layperson, this will seem like scientific semantics. But the essence of the problem is that Omicron is moving through the population faster than Delta, even if we don’t know why.

The other big question that we need to understand concerns the severity of disease caused by Omicron. Some of the excitement around this question is puzzling. All variants of Covid-19 predominantly cause disease which is relatively mild and won’t put most people in hospital or intensive care. If we’re lucky, it might be that Omicron has a lower infection fatality rate than other variants. But Omicron will still kill and many people will end up on a ventilator after catching it. For those who are hit hardest there will be nothing mild about this disease.

If Omicron is killing fewer people per 1,000 infections elsewhere in the world, we shouldn’t assume this is because it’s intrinsically less virulent than other variants either. The severity of any infectious disease is a product of both the pathogen, the person it has infected and the surrounding environment.

South African doctors are currently reporting milder symptoms for Omicron but that could well be a product of the country’s environment: an outbreak during late spring and early summer in a relatively young population is likely to be less severe than it would be in an older population heading into the winter.

In previous waves, South Africa’s infection fatality rate has been substantially lower than the UK’s. While the South Africans have not had as much exposure to vaccines, they have recently had a substantial wave of Delta variant infections which will have conferred extra immunity. If Omicron does cause fewer fatalities than we’ve seen with previous waves in the UK, it is likely to be due at least in part to widespread population immunity keeping a lid on the virus.

The expectation that Omicron is a less severe version of Covid-19 has often been fed by the hackneyed assertion that viruses always become less virulent over time. While this is a plausible theory, the idea that it always happens and is some sort of concrete certainty is trite and utterly baseless – indeed pathogens can sometimes become better at causing severe disease. Certain journalists and politicians need to drop this misleading pseudoscientific nonsense. They should remember that most people over 50 will have had measles at some point in their lives, a 2000-year-old virus which can still cause serious illness and even be fatal.

As Omicron infections seem likely to spike in the UK, policy makers face an unenviable set of decisions. Overreact and they’ll be accused of crying wolf. But if they don’t act swiftly enough, they will rightly be accused of being asleep on the job and of not having learnt the lessons of the pandemic so far.

No. 10 will be acutely aware that if they are accused of overreacting to the Omicron variant, and not just by the usual suspects, this could damage public confidence if we face another wave of infection in the future. But they should keep in mind that it is not impossible for the UK to experience the triple whammy of a more transmissible, more deadly variant which is substantially resistant to pre-existing immunity. Acting now might be the best course of action.

Indeed, Sage have this week advised ministers that they need to tighten restrictions to something equivalent to step one or two of England’s roadmap out of lockdown and do it soon if they wish to reduce the risk of hospitalisations reaching 3,000 per day, which is about the level seen at the peak of the March-April 2020 wave. That level of restrictions could see indoor social contact and hospitality reined in. According to Sage, ‘delaying until 2022 would greatly reduce the effectiveness of such interventions and make it less likely that these would prevent considerable pressure on health and care settings.’

The very first set of Covid restrictions last year which eventually led to a lockdown were aimed at suppressing the number of hospitalisations and to buy time for the NHS. ‘Squashing the sombrero’ may well be renamed ‘suppressing the spike’. In the face of the Omicron blitzkrieg, the government must maintain a cool, calm head and make the right decisions unhindered by vested interests. Only then will we be able to repel its force and remain standing.