EXPPANETIAL GROWTH it’s a dizzying thing. In the week to December 8, 536 new cases of Covid-19 were attributed to Britain, attributed to the Omicron variant, which is less than 0.5% of the number caused by the dominant Delta variant. But the week before there were only 32 cases of Omicron – and by December 14 the number of cases exceeded 10,000. It seems Omicron will become the dominant strain in the country in terms of cases before the Advent calendars run out of windows.
Cases lag behind infections. On December 13, the Minister of Health of the United Kingdom Sajid Javid said that it was estimated that there were 200,000 infections in the country that day, most of them – Omicron. Three more doublings and the total number of infections per day will be over a million.
Not only in Britain Omicron is ahead of Delta. It has already supplanted it in South Africa, where it first came under close scrutiny and where its growth, though now perhaps a little slowing, has been impressive. Studies in different European countries show similar growth, but with a later start. The same is true in America. Now the option is found in almost all countries, including China. The numbers involved are often small. But with exponential growth, the baby is not very comfortable: it does not last.
Omicron seems to have two attributes that allow it to spread so quickly. Some subset of its many mutations seem to make it more transmissible. Contact tracking studies conducted in the UK have found that the risk of spreading this Omicron infection is two to three times higher than for delta infection.
And because it better infects people who have previously been vaccinated or infected, it has a larger pool of people to infect. On December 14, Discovery Health, South Africa’s largest health insurance company, published the first results of work on Omicron conducted with the South African Medical Research Council. They found that while two doses of Pfizer-BioNTech mRNA the vaccine gave 80% protection against infection against the Omicron wave, against Omicron protection dropped to 33%. Its effectiveness in reducing the risk of serious disease is also lower: two doses of Pfizer vaccine reduced the risk by 70% (from 93% for Delta).
This still makes vaccination a very good thing. Most people who have been hospitalized with Omicron in South Africa, and 84% of those in intensive care, have not been vaccinated. And it doesn’t look like the vaccine given to someone doesn’t matter much. Another vaccine used in South Africa, produced by the American company J&J, is based on a modified adenovirus, not on mRNAto get its message in the body as it makes the more widely used AstraZeneca vaccine. It also seems to protect against serious diseases.
These real findings confirm the hope that two doses of all existing vaccines will continue to provide significant protection against serious diseases, even if they do not block infection well. It makes sense. Evolution has shaped the immune system to reduce the risk of death. Stopping re-infection with a virus seen earlier is a useful step in this direction and one of the main goals of the antibody response. But this is not the only step; protection is deep and layered. Incoming Omicron may well avoid antibodies produced by vaccines and previous infections – the chance of infecting a previously infected person is 3-8 times higher than other options. But further enemies await him.
After the onset of infection, the fight involves cellular immunity, which finds and destroys cells susceptible to the virus. This reaction is greatly enhanced by previous vaccination. And its less easy to be fooled by a few changes in the proteins on the surface of viral particles. This is why vaccines can still protect against disease, even if the antibodies they provoke no longer recognize the pathogen as well as they originally did, or if they have disappeared over time.
However, it would be good to have a better antibody response; slowing the rate of infections will slow the spread of disease and give health systems space to breathe. That’s where the vaccine vaccinations will come from. Boosters improve all forms of immunity: one of their effects is to increase antibody levels, at least for a while. This increase in quantity may in some ways compensate for the decrease in the quality of their response by reducing the risk of infection. Boosters can also improve antibody quality; the more the immune system sees the virus, the better some antibodies are tuned to it.
The reasonable expectation that vaccines provide protection against serious diseases, especially after the third stroke, is good news. Another may be that Omicron infection leads to less severe disease at all. There is some evidence of this from Gauteng, a South African province where this option is widespread. Discovery Health data show that adults with Omicron have a 29% lower risk of hospitalization compared to what was observed during the country’s first wave of Covid-19 in mid-2020. The proportion of hospitalized patients in intensive care is much lower than in previous waves, and fewer people in general wards need extra oxygen. Angelique Cutsey of the South African Medical Association, which was one of the first to raise concerns about Omicron, has consistently argued that it is a milder option.
The paper, recently submitted for peer review by Michael Chan and colleagues at the University of Hong Kong, points to one reason why this may be the case. They found that in the early days of the infection Omicron multiplied 70 times faster than Delta, in the airways leading to the lungs. But in the lungs themselves, it reproduced ten times worse than previous versions.
The details of how viruses cause disease depend not only on simple reproductive indicators. But this finding may serve as some way to explain the lower incidence of severe disease; it is the infection in the lungs that causes the most damage. And greater replication higher in the airways can improve transmissibility. Being very good at penetrating and multiplying, the airway envelope could make it easier for the virus to store in a person who has been exposed to it. Moreover, greater activity in the airways may also mean that more particles will return to the air. Signs that the symptoms of Omicron infection are more similar to the symptoms of the common cold may be consistent with this interpretation.
But neither this lab work nor the data from South Africa are strong evidence that Omicron will be much less dangerous than previous strains everywhere. South Africa data are preliminary; so far they cover only the first three weeks after infection. Typically, new waves of Covid variants begin in younger groups and over time penetrate older, more vulnerable populations. And the rate at which infection leads to serious illness and death can vary by country and population. Factors other than South African youth include the fact that most vaccinations in the country have been done relatively recently, and that a significant number have been previously infected. There may also be significant factors stemming from genetic changes or previous health histories. Things may look completely different in older populations in other parts of the world where there have been fewer infections.
Da capo, molto vivace
The degree to which an option can infect a previously infected one can also make things more iridescent than they actually are. Natalie Dean, a biostatistician from Emory University, notes that Omicron’s success in re-infecting humans may give the impression that a smaller portion will become seriously ill simply by inflating the noun. Thus, it might seem more benign, even if among those who first contracted Covid, it was as dangerous as Delta (see chart).
While the debate over the relative severity of the infection continues, health officials stress that what is important to the individual and to the health care system is not all so well coordinated. For a person, a less lethal option is preferable to a more lethal one, no matter how much it can be transmitted. For the health care system, the number of cases at any given time is a critical issue, making transmission speed very important. There is a level at which the system does not cope with the number of hospitalizations. A virus that spreads quickly can reach this level, even if it causes a lower proportion of severe cases simply because the total number of cases at any given time is very high.
To understand this, researchers from the London School of Hygiene and Tropical Medicine compared Omicron’s spread patterns to the situation in England during its worst previous peak, early 2021. Most likely makes Omicron pretty good at infecting people who have been vaccinated or infected, but also sees boosters as very good at stopping it. This will lead to a peak of hospital admissions in late January of much more than the 3,800 a day observed in 2021. This will lead to 23-30 million infections in the period from now to May 2022 and 37,000-53,000 deaths. Models from the same team have been too grim in the past, but they believe they understand why and have made appropriate adjustments.
The high prospect of hospitalization has led to the introduction of two national blockades in England: one in November 2020 and the other in January 2021. This time the government recommended working at home and reintroduced some infection control measures, such as wearing a mask on public transport. It may introduce more. But the biggest burden is to give additional injections to all adults by January 1.
In a report released on December 15, the European Center for Disease Prevention and Control warned that a number of enhanced precautions are now needed, including less contact in social and working conditions, fewer large gatherings, more wearing masks and more testing. Reducing travel and mixing between households and generations on holidays may also be in mind. Some countries are confident that tougher measures will soon follow; some people are already taking them. But if the notion that Omicron isn’t as dangerous – whether it’s justified or not – becomes widespread, people may see little reason to follow stricter rules.
Countries where Omicron rates are still very low have a little more time to prepare to learn from those who follow the curve and assess what is needed to level and lower the peak. But the growth rates observed so far strongly suggest that time is best measured in days and maybe weeks. Exponential growth is a dizzying thing. ■
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