Covid-19: how the end of a pandemic is determined

The news that São Paulo and eight other states did not record any deaths by Covid-19 on Monday (8) was received with much celebration and optimism.

Although the event is symbolic and reinforces the continuous improvement of the pandemic in the country over the last few months, experts heard by BBC News Brasil understand that it is necessary to put the fact in perspective and keep in mind that there is still a long way to go before decreeing the end of the health crisis.

“We are in fact in the best phase since the beginning of 2021, with a huge decrease in cases, hospitalizations and deaths. But the announcements that no one died from Covid-19 should be analyzed with caution, not least because there is a delay in notifications”, ponders the doctor Guilherme Werneck, member of the Brazilian Association of Collective Health (Abrasco).

“And it must be made clear that the end of the pandemic, when we really get there, will not mean the end of covid”, completes the health professional, who is also a professor at the Institute of Social Medicine at the State University of Rio de Janeiro (UERJ) .

Virologist Paulo Eduardo Brandão, from the Faculty of Veterinary Medicine and Animal Science at the University of São Paulo (USP), agrees. “Based on what we know about other types of coronaviruses, it is likely that Sars-CoV-2 [o responsável pela pandemia atual] lessens over the years and becomes a common cold cause. But the current re-emergence of cases in Europe shows that we are still far from that”, he analyzes.

Physician Lucia Pellanda, professor of epidemiology and dean of the Federal University of Health Sciences of Porto Alegre, highlights the importance of collective health and the global nature of the challenge we face. “As the name implies, the pandemic is a worldwide problem. And as long as the situation is bad in one region, we will all remain at risk.”

But how do we get here? And what are the most optimistic and most pessimistic prospects for the coming months? Understand below how a pandemic ends – and what can happen after it.

Positive scenario in Brazil and worrying in Europe

After a very tough first semester, with hundreds of thousands of cases and deaths by Covid-19, Brazil has been in a much calmer situation since the end of July and the beginning of August.

To get an idea, the daily moving average of deaths (which takes into account the records of the last seven days) is currently at 236, according to the panel of the National Council of Health Secretaries (Conass).

Such a number had only been observed in April 2020, when the virus began to spread across the country. At the worst moment of the health crisis, this rate reached, in April 2021, a peak of 3,124 daily deaths.

The sequence of good news culminated in the news, released on Monday, that São Paulo did not record any death by Covid-19 in 24 hours, a fact that had not happened once since the beginning of the health crisis.

On that same day, eight other Brazilian states had no deaths from the disease: Acre, Amapá, Goiás, Minas Gerais, Piauí, Rondônia, Roraima and Sergipe. Acre, by the way, has had no record of death for over ten days.

According to experts, there are three ingredients that help explain this improvement.

“It is evident that vaccination is the main one. As of June, when the campaign gained momentum and vaccination coverage in the Brazilian population increased, we had a substantial drop in hospitalizations and deaths”, observes Werneck.

“We cannot forget also the huge number of cases we had, which certainly contributed to create immunity, and adherence to non-pharmacological measures, especially the use of masks”, complements the doctor.

The milder scenario allowed many Brazilian cities to alleviate restrictions, which maintained living spaces, such as restaurants, bars and shopping malls, closed or with very low opening hours and occupancy rate.

Some mayors and governors have gone further and even more recently released the use of masks in some open spaces.

Experts, however, fear that this wave of optimism and relaxation will reverse the positive trend and squander all the achievements of the moment.

“Of course, the news of a day without deaths is excellent, but you can’t celebrate too much. This is an isolated date and, when we look at the statistics, we still have reasonable averages of cases and deaths per covid”, says the physician Leonardo Weissmann, consultant of the Brazilian Society of Infectology.

“We have to be careful so that the situation in Brazil doesn’t get worse again, as it happens now in Europe, which has a new rise in cases and hospitalizations after reopening”, points out the specialist.

According to the World Health Organization (WHO), Europe is once again the epicenter of the pandemic, with a considerable worsening of the situation in the United Kingdom, Germany, Hungary, Austria and Ukraine.

During a press conference on November 4, Hans Kluge, WHO regional director, said the situation was a “grave concern” and that the region was “at a critical point for pandemic resurgence”.

The explanation for this resurgence, according to the assessment of the organization’s own representative, is the relaxation of non-pharmacological measures, such as the use of masks and the prevention of agglomerations, and the low rate of vaccination in some countries.

It is not possible to say that the same scenario will happen in Brazil (not least because the immunization campaign here has greater popular participation), but, until now, the worsening of the scenario in Europe was repeated a few months later in our country.

“It is possible to escape this, depending on the behavior of people and public policies. We need to continue with vaccination and continue with the layers of protection, such as the use of masks and care with agglomerations and with the circulation of air through the environments” , indicates Pellanda.

How does a pandemic end?

For some time, the possibility was raised that mass immunity (or herd immunity) would be able to put an end to Covid-19: as people got sick (or, preferably, were vaccinated) the Sars-CoV-2 it would find no more hosts and would cease to circulate.

But the emergence of new variants such as alpha, beta, gamma and delta, along with the knowledge that immunity against this coronavirus does not last forever and varies widely from person to person, has practically ruled out that idea.

Today, there is greater agreement among scientists that the Covid-19 pandemic will gradually develop into an endemic one.

This means that the disease will continue to be common in one (or several) regions of the planet, with a number of cases and expected deaths every year.

This is what happens with a series of other illnesses, such as malaria, yellow fever or the flu itself.

“The challenge will be to establish an admissible level of cases and deaths, which will require a consensus not only from the scientific community, but from the entire society”, foresees Werneck.

“And to prevent these numbers from rising again and having outbreaks or epidemics in the future, we need a very strong surveillance system, capable of detecting sudden increases and using preventive measures. This is what happens today with meningitis and measles “, exemplifies the doctor.

Pellanda agrees with this difficulty in establishing the criteria that will determine the end of the current pandemic.

“We are in a period of data instability and we are not sure what the future will be like. Therefore, we should be wary of anyone who is very sure now of what will happen,” he says.

examples from the past

To understand Sars-CoV-2’s next steps, Brandão draws a historical parallel with another type of coronavirus, OC43, which possibly caused an epidemic (or even a pandemic) in the late 19th century.

“You may have never heard of it, but you’ve probably been infected with this virus a few times,” jokes the scientist.

“After having ‘jumped’ from cattle to humans, he was aggressive. But, over time, it was attenuated by successive cycles of infection in our species. Currently, OC43 is one of the main causes of the common cold, a condition that it’s self-limiting and doesn’t usually cause more severe symptoms,” he says.

The virologist reminds you that the “main goal” of a virus is to replicate, not kill its host. Therefore, an infectious agent that manages to create this “peaceful coexistence” with the human being ends up reaching its objective more easily and remains among us for a long time.

On the other hand, a very aggressive virus, which kills quickly after infection, is less likely to cause an epidemic or a pandemic, as transmission ends up impaired.

This is what happens, for example, with Mers-CoV, another type of coronavirus responsible for the Respiratory Syndrome of the Middle East (or Mers, for its acronym in English): its lethality rate reaches 37%, but the cases remained restricted to some countries in 2011 and 2015.

Will this attenuation phenomenon happen with Sars-CoV-2? You can’t be sure about that.

“We live in a moment when this coronavirus is making its first rounds around the Earth. There have been two and it is in its third, with the recent increase in transmission across Europe”, explains Brandão.

“For now, it is not possible to categorically state that Sars-CoV-2 will be milder, like the OC43. In evolutionary terms, this is a possibility that may take a few years to happen,” he continues.

“Therefore, it is not time to let our guard down. This coronavirus is not attenuated and the relationship is not friendly enough to the point that we let it circulate freely around our house”, completes the researcher.

In this same line of reasoning, the diametrically opposite possibility is also not ruled out: the emergence of variants of the coronavirus that are even more aggressive and capable of circumventing the protection of available vaccines.

“This is a mathematical reality: the more the virus replicates, the more versions of it appear and, consequently, the greater the risk of worrying mutations appearing”, confirms Brandão.

And this only reinforces the idea that the problem is global and should be treated as such. “In some poorer nations, the proportion of vaccinees remains very low. This opens the risk of pockets of Covid-19 that could ‘export’ the virus again to the rest of the world”, warns Pellanda.

“The pandemic reinforced the notion that all health is collective and is connected with people around and with the entire planet. As long as one human being is in danger, we will all be”, adds the doctor.

It is precisely for this reason that specialists hit the button so much on vaccination and other non-pharmacological care (use of masks, avoiding agglomerations, precautions with ventilation…).

Preventive measures can even be somewhat alleviated if the current situation in a country or region is good, but it is not possible to abandon them completely (as has been done in some European countries), at least for the next few months or years.

The same reasoning also applies to immunization: it is likely that we will have new doses of vaccines against Covid-19 from time to time.

Although the end of the pandemic is still shrouded in mystery and seems just a distant prospect, Brandão recalls a speech made by then-British Prime Minister Winston Churchill in 1942, in the middle of World War II, after a major victory by the Allies against the Nazis.

In the virologist’s view, the phrase applies perfectly to Covid-19’s current stage in the world: “This isn’t the end. It’s not even the beginning of the end. But it is, perhaps, the end of the beginning.”