Everything the scientists know right now about Omicron: How soon does booster protection kick in? Why are the symptoms different from the Delta variant? And can lateral flow tests spot it? Leading experts answer the vital questions

FILE PHOTO: Test tubes labelled "COVID-19 Test Positive" are seen in front of displayed words "OMICRON SARS-COV-2" in this illustration taken December 11, 2021. REUTERS/Dado Ruvic/Illustration

How bad is Omicron if you get it?

The evidence so far suggests the infection is generally mild and may damage the lungs less than Delta and the original Wuhan strain.

According to research by Cambridge University, Omicron appears less efficient at infecting cells in the deep part of the lungs, which can lead to severe illness.

‘Reports from South Africa show there has been surprisingly little serious disease with the Omicron variant for the number of cases recorded,’ says Andrew Preston, a professor of microbial pathogenesis at Bath University.

However, he adds: ‘We should be cautious about extrapolating this experience to the UK because the profile of our population is very different.

‘The UK suffered relatively badly in the first wave, suggesting our population has a higher predisposition to suffering serious disease.

‘The level of immunity also differs between the two populations and the other infectious diseases experienced during the lifetime of a South African and a UK resident is different, and this can affect how they respond to particular infections.’

Ultimately, how ill you get with Covid is down to a number of factors, including underlying health conditions such as type 2 diabetes, says Will Irving, professor of virology at Nottingham University.

‘In general, it’s down to a combination of how rapidly your immune system responds and the size of the infecting dose’ — in other words, how many virus particles you inhale.

‘It’s then a race between the pathogen replicating and the body’s attempts to eliminate the pathogen.

‘The benefit of vaccination is that it speeds up the body’s response and makes it more likely that the immune system will win the race before serious disease develops.’

Why are the symptoms so different?

Early data suggests symptoms of Omicron are more similar to those of the common cold: runny nose, headache, fatigue — either mild or severe — sneezing and sore throat, rather than the classic Covid symptoms such as loss of taste and smell, says Professor Preston.

‘This may be because Omicron has a number of mutations that make it different from previous variants,’ he adds.

‘For example, Omicron has 50 mutations, including 32 in the S gene, the gene that encodes the virus’s spike protein which allows it to access our cells.

‘This compares with up to 13 mutations on the S gene with Delta. It is possible some of these mutations alter its interaction with our bodies, and this changes the pattern of symptoms caused by Omicron infection.’

Another factor, he suggests, is that ‘higher levels of immunity’ in the population may alter the way Omicron interacts with our bodies, ‘limiting the amount of virus that accumulates or tissues the virus reaches.

‘There are also more respiratory viruses circulating this year — such as colds and flu — and this could also change the pattern of symptoms, as they can stimulate a general immune response in the body, causing symptoms such as fever, which is designed to slow down the reproduction of pathogens.’

Why is Omicron so infectious?

‘The mutations that have occurred in Omicron make it better able to infect the body,’ says Professor Preston. ‘There is some evidence to suggest that it is able to bind to the ACE2 receptor more tightly, facilitating its infection of our cells.’ ACE2 receptors are proteins found on the surface of many types of cells and the route the virus uses to infect them.

‘Also, Omicron is more able to evade immunity, from either vaccination or prior infection, so is able to infect people that other variants can’t,’ he says.

But there are some advantages. Omicron spreads rapidly because only a small amount of virus is needed to infect someone, says Tim Spector, professor of genetic epidemiology at King’s College London, who runs the ZOE Covid tracking app.

‘The symptoms appear quicker — two days after contact — and seem to last less time. This is not ideal for the virus as people are shedding less virus for less time, and are less likely to pass it on unwittingly.’

Could I catch Delta and then Omicron?

‘In short, yes,’ says Professor Preston. ‘Omicron in particular appears to be able to overcome the protection generated by both prior infection with another Covid variant such as Delta and prior vaccination.

‘This is not unusual; Delta was able to evade to some extent the immunity stimulated by the Alpha variant. The good news is that it’s almost certain any symptoms will be milder than if you hadn’t been previously infected or vaccinated.’

I’m vaccinated. Will I catch Omicron?

Two doses of Covid vaccine offer far less protection against the new Omicron variant than against Delta.

Initial data suggests that 25 weeks after the second jab your level of protection against Omicron ranges from 10 per cent to 40 per cent depending on the jab you had, according to an analysis by the UK Health Security Agency (UKHSA) earlier this month. Two doses of the AstraZeneca vaccine offered 40 per cent protection against symptomatic infection with Delta and possibly less than 10 per cent against Omicron.

For two doses of the Pfizer jab, the figures were 60 per cent and under 40 per cent respectively.

Similar results emerged from research by Columbia University in the U.S. published last week, which found that Omicron is ‘markedly resistant’ to all four Covid vaccines.

Dr Susan Hopkins, the chief medical adviser for UKHSA, said: ‘I think what we’re seeing is that if you’ve had two doses more than three months ago, then it’s not going to prevent you from getting symptomatic disease.’

However, the same analysis found that a booster jab increases protection to more than 70 per cent. This was backed by data from Imperial College, published last week, which suggests that two weeks after a second dose of vaccine, protection against Omicron is between 0 and 20 per cent; but this rises to between 55 and 80 per cent following a booster.

One reason for this is that, even though boosters aren’t designed for the Omicron variant specifically, they trigger the body into making more antibodies.

Antibodies are proteins produced by the immune system when it is under threat to seek out and destroy bugs and viruses.

And research has found that it is quantities of antibodies against SARS-CoV-2 (the virus that causes Covid) that count, even if they are not particular to that variant.

Other studies suggest that killer T-cells, which are also triggered by a vaccine, retain much of their ability to target the virus even when it is a new variant.

‘We still expect two doses of vaccine to dramatically decrease your risk of suffering serious disease from Omicron, compared to unvaccinated individuals, but it’s clear that boosters offer significantly greater protection against disease, and this is very likely to also translate into decreasing the amount of transmission as well,’ says Professor Preston.

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