Covid: why some scientists are comparing the omicron variant of the coronavirus to measles

Spanish immunologist Alfredo Corell recently caused controversy by claiming that the omicron variant of SARS-CoV-2 is as contagious as measles, one of the most contagious viruses in the world.

Obviously, the coronavirus does not produce the same symptoms as measles. But Corell’s claim refers to its transmissibility, not its symptoms.

And in that sense he is absolutely right.

The omicron variant has caused great furor since the first moment it was detected in South Africa, as it accumulates a large number of mutations in proteins that facilitate the entry of the virus into our body.

The initial political and media uproar was not due to the greater severity of the symptoms, but to their greater capacity for infection.

But, as with previous variants, when a new variant is detected, it is already circulating among the population.

Therefore, all the care of governments with the closing of borders was useless. Now, in several countries, the omicron variant is prevailing over the previous ones, including the delta, until then the most transmissible.

It is this increased infectivity, as high as that of measles, that makes omicron more worrisome than other variants.

But what is the infective capacity of the omicron variant?

To determine the dispersal ability of a pathogenic organism, a parameter known as the base number or base reproduction rate (R₀) is applied.

It is nothing more than the average number of new cases that a positive case generates during a period of infection. For example, if a pathogen has an R₀ of 2, it means that one infected person will infect two others, on average.

And this already causes the number of infected to increase exponentially.

The R₀ parameter is inherent to viruses, but it can vary depending on conditions and is directly dependent on the number of contacts.

In cases of pandemic, it is essential to reduce the R₀ through containment or quarantine measures to prevent an infected person from infecting others. Only then is R₀ reduced.

Thus, if the R₀ reaches a value lower than 1, the pathogen disappears over time. On the other hand, if it is bigger, the contagion increases.

Among the most contagious pathogens, we find the measles virus, which is airborne and whose R₀ is between 12 and 18.

Just below it are whooping cough, with an R₀ from 12 to 17; diphtheria, 6 to 7; smallpox, polio, and rubella, with an R₀ of 5 to 7.

Interestingly, although they are very contagious pathogens, they have all been controlled thanks to vaccines. For all of them, except for smallpox which has been eradicated, we have vaccines within the official calendar that are injected in the first years of life.

In other words, despite their high capacity for contagion, these pathogens no longer cause us illnesses, except for outbreaks that occurred mainly in unvaccinated groups, as we are immunized from childhood.

And the R₀ of different SARS-CoV-2 variants increased as the virus spread among humans.

A recently published study indicates that the R₀ of the early Wuhan variant in China was 2.5.

For the more transferable delta variant, the R₀ was about 7.

The omicron’s is 10 — and that means it has a high chance of becoming the prevalent variant in the world.

To put it into context, the 1918 flu had an R₀ between 1.4 and 2.3, lower than that of the coronavirus and much lower than that of the current variant.

To which we must add a situation of global mobility much more limited than today.

And there is the problem.

Another important aspect is that both viruses, measles and coronaviruses, use the same transmission route: the air.

Despite early hesitations about its contagion mechanism, it is already clear that SARS-CoV-2 is mainly transmitted by aerosols. And this is also another important factor for its dispersion.

Although there are other viruses such as HIV (4.2 to 10.6), hepatitis C (2.1 to 3.9) and Ebola (1.2 to 1.9) that present a worrying R₀, their transmission mechanism is easily controllable .

But in the case of an airborne virus, with a high R₀ and a long pre-symptomatic period, contacts are almost impossible to avoid.

To all this we must add the fact that many infected people suffer the infection asymptomatically.

The latest studies in Spain show that 30% of those infected passed the infection asymptomatically or with symptoms so mild that they do not require special attention.

This makes the spread of the virus even more uncontrollable, as many people may be contributing to the spread without realizing it.

New conditions, new solutions

Viruses evolve, especially if they manage to infect a new host.

The initial conditions of the pandemic required drastic measures to prevent mass infections and the collapse of health systems.

With no antivirals, no effective therapies, no proven clinical protocols, and no vaccines, we were all at the mercy of the virus.

Now, the majority of the population is vaccinated with the complete vaccine schedule and their immune system contains memory cells prepared to be detected and activated quickly, even more so with the boost of the third dose.

Only a small number of low-immune and unvaccinated people are in real danger.

Data from Spain show that unvaccinated people are at 20 times greater risk of hospitalization, admission to the ICU or dying from covid-19 than those who are vaccinated.

With this situation, the debate about the measures that should and should not be taken becomes very complex.

A constantly changing landscape, a more contagious virus and a high percentage of the vaccinated population are important factors that affect decisions.

As is already partially done in the case of seasonal flu, monitoring symptomatic cases, strengthening primary and emergency care and vaccination are the most appropriate health measures.

Citizens can contribute by reducing contacts as much as possible and avoiding situations that favor the spread of the virus.

The only defense and escape from this pandemic is immunity and avoidance of contact if you are infected. Thus, we will reach the balance that already exists with the four human coronaviruses that cause colds and that have already traveled the same path that the current SARS-CoV-2 is taking.

Guillermo López Lluch he is a member of the Spanish Society of Cell Biology, the Spanish Society of Biochemistry and Molecular Biology, the Spanish Society of Geriatrics and Gerontology, the Society for Free Radical Research and the International Association of Coenzyme Q10.

This article originally appeared on The Conversation website.