A scientist’s guide to understanding Omicron

Over the coming days and weeks, scientists from around the world will be sharing early information about the new Omicron variant of SARS-CoV-2. We are two researchers who study the evolution of viruses, and we will be keeping a close eye on the data as it becomes public. This new research will range from laboratory studies investigating how the virus interacts with antibodies to observations of patient outcomes to large-scale data on infections and hospitalizations. The data will try to answer three key questions, all of which are important to understanding the risk of Omicron.

How well can Omicron dodge the antibodies we have from vaccines and prior infections?

Omicron has many mutations, especially in the spike protein that is the main target of the antibodies generated by vaccination and prior infection. This is why scientists were concerned it could evade the defenses built by vaccines or by having had Covid-19. Lab experiments have already shown that Omicron has mutations that reduce the infection-blocking ability of antibodies to about one-fortieth of their effectiveness against an earlier version of the virus.

There is solid evidence that this increased antibody resistance of Omicron will lead to more infections among the vaccinated and previously infected. A study from South Africa found a higher rate of people getting infected a second time with Omicron than with previous waves caused by the Beta and Delta variants. Omicron has also caused some mild to moderate infections in individuals who were both vaccinated and had received a booster shot. An early report from Britain estimates that vaccine effectiveness against disease with symptoms is lower against Omicron than against Delta.

These early findings suggest that vaccines may not protect as well against infections as they did previously. And there’s a chance Omicron-specific boosters may be needed in the future.

Will the immunity we have still protect us against severe disease?

Even if some antibodies fail to block infection by Omicron, T cells and other antibodies developed from vaccination or infection may provide some protection against severe illness. In other words, deaths and hospitalizations may not track cases as closely as they have in previous pandemic waves. Measuring this requires data from clinics, hospitals and epidemiological studies that follow infections and symptoms in people over time. Such studies take more time than experiments in a lab.

It typically takes several weeks for severe Covid-19 to develop, which is why deaths and hospitalizations are what scientists call a “lagging indicator.” So while it’s fine to be optimistic when we hear early anecdotal reports about vaccinated people having only mild symptoms, remember that it will take time to have reliable data on disease severity overall. For example, it’s possible that Omicron could cause milder disease in people who have been previously vaccinated or infected but cause severe disease in people with no immunity. This will have implications for the burden that might be placed on hospitals.

Is Omicron more contagious than Delta?

We know that Omicron transmits well because it is causing an increasing number of cases in many countries. There are two factors that could contribute to this: Omicron may have a strong ability to infect people with no immunity, and it may have an increased ability to infect people with prior immunity from vaccinations or previous infections.

The balance of these two factors will determine whether Omicron is more transmissible than Delta in all populations, or just in places like South Africa and other countries, where there is a lot of immunity from people being infected previously. To better understand Omicron’s transmissibility, scientists will need to measure its rate of growth relative to other variants among different groups of people. Answering this question could help predict the timing of potential hospital surges.

What the answers will tell us

There are a few different scenarios for Omicron.

One is that Omicron is so transmissible that it spreads around the world and outcompetes all other variants, including Delta, so that, in the future, all new viruses are descended from Omicron. This scenario happened in mid-2020 with a variant called D614G (this was before variants were given Greek names) from which all subsequent variants are descended.

Another scenario is that Omicron spreads in some locations but ultimately turns out to be less transmissible than other variants and eventually falls out of the picture. This happened with Alpha and Beta in the first part of 2021.

Regardless of whether Omicron fully displaces other variants, it appears likely to cause a surge in cases around the world. The extent of this surge will depend on the level of immunity in different populations, the public health measures in force and the effects of factors like seasonal changes in temperature and humidity on transmission, which so far are poorly understood.

If Omicron causes a rise in cases but less severe disease than Delta, that would certainly be good news. But if it spreads widely, it could still send a large number of people to the hospital. Also remember that it’s possible Omicron is at least as severe as Delta in people without immunity. We also don’t yet understand the long-term health consequences of having Covid-19, and it will take weeks to understand how Omicron affects groups of people with different levels of immunity.

The measures that control the spread of other variants are also expected to help against Omicron. This includes increasing vaccination coverage, supporting rapid mass testing, improving indoor ventilation, encouraging the use of masks (as well as upgrading to higher-quality masks) and helping people identify when they are infected, making it easier to isolate. There is evidence that getting a booster increases protection beyond that provided by just the primary vaccine series.

Given the extensive mutations in Omicron, it may also be necessary to make Omicron-specific vaccines.

Embracing these measures while monitoring the unknowns will help strike a balance between reducing risk while still enjoying our lives. That’s what scientists, like everyone else, are hoping for.