A reflection on the future of SARS-CoV-2 based on epidemiology studies. The goal is no longer the elimination, but to have an endemic virus (except for new variants). Only one virus in the world has been eradicated: smallpox. Here’s why
The variant Omicron put an end to the pandemic? Perhaps it will mark the end of the first pandemic phase of the SARS-CoV-2 virus circulation, but it will hardly mark its elimination.
Doctor Anthony Fauci, medical consultant to US President Biden for Covid, traced the path of the evolution of the virus by speaking (live streaming at the World Economic Forum) of the 5 pandemic phases: The world still in the first stage – said Fauci -, with a still very negative impact on the entire globe. The next steps are
– the deceleration,
– the check,
– elimination And
– eradication.
In the control phase, the virus will become a non-destructive presence and will be considered endemic.
What are the characteristics of the 5 phases of a pandemic mentioned by Fauci? We asked Paolo Bonanni, epidemiologist and Ordinary of Hygiene at the University of Florence.
1. The first phase: active pandemic, critical impact.
Pandemics arise when there is a new infectious agent that appears on the scene and acquires one large transmission capacity within the human species. The whole population is susceptible at this stage, because the virus has never been seen by the immune system before. The five phases concern the evolution of each pandemic; the first is that of the active pandemic, with a strong negative impact (such as the one we suffer today) on the population and health systems.
2. The second phase: deceleration
The deceleration due to the fact that people gradually become infected and acquire an immunity (which can be more or less lasting). When there was the Spanish flu pandemic there were no vaccines, then the deceleration was linked to the huge number of infected people. In the case of Covid, together with the healed, there are also people who acquire immunity thanks to vaccines.
3. The third phase: control (or endemic phase)
Controlling an infection means reducing the morbidity of the disease to such a degree that is no longer a public health issue. The goal can now be pursued through mass vaccination. The endemic phase is the one that has, for example, the seasonal flu virus: it is not so true, however, that it does not completely create public health problems, given that every year the vaccination campaign must be renewed and every year the flu costs between 8,000 and 10,000 human lives; we say that in any case a “controlled and managed” disease.
4. The fourth phase: elimination.
Eliminating an infectious disease means that that disease is no longer detected for at least three years in a given geographic area, as has happened with polio in the WHO European region since 2001. The virus, in the elimination phase, however, is not extinct: it could be present in environmental reservoirs (for a virus transmitted with feces, for example, in sewage), or be brought from abroad, or circulate asymptomatically.
5. The fifth phase: eradication.
When you get the phasing out of a particular virus around the world, eradication can be achieved, which no longer only affects infectious disease, but also involves infection. When an infectious agent has been eradicated, it means that it has been eliminated from the globe. The only infectious disease that has been eradicated so far is smallpox.
How come this only happened with a virus?
It is very difficult to eradicate an infection: practically the entire world population must be practically immune and the possibility of eradication also depends on the R0, that parameter that we have learned to know which measures the basic contagiousness rate of infectious agents (before the introduction containment measures): if an infectious agent is very contagious, it is necessary to have a very high immune coverage to eradicate it. the easier it is to eradicate an infectious agent the lower its R0.
For this reason, with the advent of Omicron, it was said that the eradication of SARS-CoV-2 would become almost impossible?
To clarify with an example, measles has no variants, but it has a very high R0, around 15-20, and therefore, although we have an exceptionally effective vaccine that even reaches almost 99% effectiveness, we have not yet been able to eliminate it. With current vaccines (which are exceptionally effective in preventing the consequences of the disease, but not as effective in preventing infections), eradication is not a plausible hypothesis.
too early to understand how Omicron will change the course of the pandemic – said Fauci -. It would be just a coincidence if we didn’t have another variant that escapes the immune response. Which road remains?
The problem is that immunity must be permanent and that it also covers us against the new variants of the virus that could circulate – says Bonanni -. A target for the vaccine should be found that does not change in the different variants, but it seems quite unlikely. In other words, it would be necessary to find a universal vaccine that very effectively prevents transmission regardless of variants.
Is it tolerable to aim to make SARS-CoV-2 endemic?
We can do this by further increasing vaccination coverage and third doses, the effect of which is combined with natural infections. For the numbers we currently have, it would be desirable to have an endemic infection with the same level of severity as the flu. If we were able to carry out an exceptional vaccination campaign all over the world we could be more relaxed, but we are still far from the objectives and this exposes us to the possibility of new emergencies linked to new variants. If we want to take the flu as a model, however, let’s remember that it appears as a rather mild infection, but the infectious disease that does the most damage in our population (before the arrival of Covid). How to manage an endemic virus and the socially acceptable thresholds of lethality and danger are parameters that must be decided at the level of public health and politics, concludes Bonanni.
January 18, 2022 (change January 18, 2022 | 14:13)
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