How much more dangerous could the coronavirus become?

The delta variant, which is more infectious and possibly more pathogenic than the original SARS-CoV-2, begs the question: could evolution make the coronavirus worse, and by how much? Vox tried to find an answer.

Scientists say about each new variant with different properties that its appearance was expected. But they cannot predict how evolution will proceed. The genetic code of the coronavirus consists of about 30 thousand “letters”. This is relatively small, but it still gives too many possible mutations to test each one. In addition, sometimes mutations only play a role in combination with other mutations, which makes the task much more difficult.

In viruses, we are interested in three properties: contagiousness (how easily it is transmitted), virulence (how severe the disease causes), and the ability to elude the immune system. Probably, these properties cannot be amplified indefinitely: if the virus infects or kills all people, it cannot be transmitted further. But where the limit lies, no one knows.

Some properties can develop to the detriment of others. For example, it can be assumed that a virus that is invulnerable to antibodies produced after illness or vaccination will be less effective in infecting human cells, because antibodies are mainly labeled in the place where SARS-CoV-2 binds to our receptors. But for now, this is just a guess.

It can be said with greater confidence that the coronavirus is unlikely to find new routes of transmission. It is now airborne – no need to worry about contaminated surfaces someday. The same applies to other properties: the existing ones can change in one direction or the other, but new ones, most likely, will not appear.

It is also likely that the evolution of SARS-CoV-2 will gradually slow down: this is indicated by other viruses. But we are not talking about months, but about years.

The more people are infected, the more likely the virus is to mutate. Also, therefore, you need to continue vaccination.

Why is the incidence of disease declining in the UK, although the restrictions have been lifted?
The gloomy predictions did not come true. Despite the lifting of almost all restrictions, the number of new cases of COVID-19 in the UK has more than halved in two weeks: from 54.7 thousand to 22.3 thousand Scientists are at a loss as to why this is happening, but another rise is expected in the fall morbidity. Writes about this Nature.

It is likely that the current decline is not due to herd immunity. The number of new cases of COVID-19 is falling throughout the country, and herd immunity, in theory, is achieved unevenly. In the UK, 70% of adults are fully vaccinated, but vulnerable people are still plentiful. Mostly people are sick at the age of 16-24 years, among whom many are not vaccinated or received only one dose.

Perhaps the decline is so significant because the peak in mid-July was very high. Last but not least, it was driven by the European Football Championship, when people got together to watch games. The championship is over.

The UK uses a government-owned mobile contact tracing application. During and shortly after the championship, many were alerted to contact with the infected and were forced to stay at home. Maybe this also slowed down the spread of the virus.

Around July 23, schools in England closed for the holidays. Since then, too little time has passed for this to significantly affect the statistics, but some of the students finished their studies even earlier, and about 20% were in isolation due to contact with infected people.

Other factors could have played a role: good weather, which caused the British to get out into the street; fewer tests for COVID-19 (although the proportion of positive tests also decreased).

Some data indicate that the number of infections has crept up again, but it will be safe to talk about this in a few days or weeks. Further, much will depend on the behavior of people, and it cannot be predicted. Scotland peaked a little earlier than England, and the incidence there remains low so far. But in September, schoolchildren and students will return to classes, and workers to offices, in addition, the protection of the first vaccinated by that time may weaken, so in the fall it is worth waiting for another wave of COVID-19.

Will children have to be vaccinated?
Because of the “delta” variant, all people over the age of five must be vaccinated in order to develop herd immunity. But herd immunity is not the only goal to strive for. Australian epidemiologist Emma McBride writes about this in a column for The Conversation.

In Australia, they argue about how to continue to live during a pandemic. According to the model, which is guided by the government of the country, it is required to vaccinate 70-80% of adults – then the restrictions can be lifted. McBride and her colleagues built a different model. According to her, vaccinating even all adults will not be enough.

When setting up the model, the scientists assumed that an infected with the “delta” variant would transmit the virus to an average of five to ten people. Due to the increased contagiousness, this indicator is at least twice as high as m for the original SARS-CoV-2. Also, McBride and her colleagues took into account that the frequency of contact between people depends on age, and those close to age are in contact with each other more often. Finally, the model assumes that after vaccination you can get infected, get sick, and transmit the virus to others.

The simplest calculations show that in the case of the Wuhan variant of the virus, 60% of people need to be vaccinated to form herd immunity, and with the “delta” – already in the region of 80%. But given the differences between age groups, the situation is even worse. Because of the high contagiousness of the delta, children will infect each other, even if most adults are vaccinated. It is also known that the effectiveness of the AstraZeneca and Pfizer vaccines is reduced with this option.

If an infected “delta” transmits the virus to an average of five people, then herd immunity will be formed if 85% of people are vaccinated, including children from five years old. Without this, you will have to leave some restrictions: masks, distance. But you can avoid getting hung up on the number of new cases of COVID-19 and try to protect the most vulnerable.

Herd immunity is not the only goal to be pursued. A high level of vaccination still reduces the risks for those who cannot or do not want to be vaccinated, and even more so for the vaccinated themselves. Vaccinating the elderly and people at risk first is a smart decision. Then you should focus on the key carriers of the virus. In Australia, these are older adolescents and young adults. Whether to vaccinate children is a controversial issue. But when discussing it, one should take into account the possible benefits of collective protection and the return of freedoms.

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