Covid: what happens to our body each day of the coronavirus infection

In recent weeks, cases of Covid-19 have not stopped growing in Brazil. According to the panel of the National Council of Health Secretaries (Conass), the daily moving average of new infections is currently at 56 thousand. Just over a month ago, that number was at 13,000, a rate four times lower.

This increase, related to the circulation of more infectious variants and the relaxation of protective measures, leads us to think about the action of Sars-CoV-2, the coronavirus responsible for the current pandemic, and how it manages to spread so easily.

In this BBC News Brasil report, you will get to know in detail the “path” it takes through our body and what happens every day from the moment we have the first contact with the pathogen.

But, before getting into the details, an important caveat: the dates presented are only average estimates, based on information published in scientific studies and reviewed by national and international health agencies. These deadlines may vary, more or less, in specific cases.

Day 0: the infection

It all starts when we have close contact with someone who is already infected with the coronavirus.

When that person talks, sings, coughs or sneezes, they release tiny droplets or aerosols of saliva that carry Sars-CoV-2 particles.

The amount of virus varies considerably from individual to individual. “Some have a low load, 10,000 viral copies per milliliter of saliva”, calculates virologist José Eduardo Levi, research and development coordinator at Dasa.

“The average load ranges from 10,000 to 1 million particles, but we see some that carry up to 1 billion viral copies per ml”, compares the specialist, who is also a researcher at the Institute of Tropical Medicine at the University of São Paulo.

These tiny infected droplets can be thrown directly onto our face — or remain in suspension, “wandering” through the environment for minutes or even hours (in a dynamic very similar to cigarette smoke), depending on the air circulation of the environment in each place. . In this second case, we ourselves inhale these aerosols during breathing.

And this is where the infection process really begins. Sars-CoV-2 uses the spike (also known as spike or protein S), which is located on the surface of its structure, to connect to receptors on the mucosal cells of the nose, mouth and even the eyes.

From there, it will start the routine common to any virus: invade the cell and use all the biological machinery to incessantly create new copies of itself.

“In this replication, it produces from 100 to 1,000 new viruses in a single cell”, estimates Levi.

“This is such a large number that the cell cannot take it, it bursts and dies. These viruses are then released and will repeat this process in neighboring cells.”

This massive replication, by the way, has to do with the emergence of variants of the coronavirus. Not all copies come out the same and some have important genetic mutations.

If this change in the genome represents any advantage for the virus, it opens the way for the emergence and spread of new strains of concern — such as the already known alpha, beta, gamma, delta and omicron.

Days 1, 2 and 3: Incubation

After Sars-CoV-2 manages to invade the first cells of our body, the next step involves “gaining ground” and expanding the spectrum of action.

The thousands of copies that are released from each invaded cell advance further and further through the body — if they start working on the surface of the face, then they are inside the nose, down to the throat and eventually reaching the lungs.

This period of silent evolution, in which the presence of the virus does not yield any clues, is known among experts as incubation.

“And we have noticed in recent months that the incubation time of the new variants has decreased”, observes virologist Anderson F. Brito, a scientific researcher at the Todos pela Saúde Institute.

According to a report by the UK Health Safety Agency, the incubation of the alpha variant lasted an average of five to six days.

During the delta lineage wave, that window dropped to four days.

In the omnitron, the period between the viral invasion and the onset of symptoms has been reduced further and is only three days.

In other words: if before the person had contact with someone infected and it took almost a week to show the typical signs of Covid, currently this process is much faster and can happen almost overnight.

It is worth mentioning here that the incubation time may vary: in some cases, symptoms appear up to 14 days after the initial contact with the virus.

Days 4 to 14: The onset and course of symptoms

As the virus progresses through the upper airways (nose, mouth and throat), it eventually catches the attention of our immune system, which starts a counterattack.

The first line of defense involves cells such as neutrophils, monocytes, and Natural killers (natural terminators, in literal translation), as detailed in an article published in 2021 by two researchers at Zhejiang University Hospital in China.

Over time, other immune units come into play, such as T lymphocytes, which coordinate a more organized response to viral invasion, and B lymphocytes, which release antibodies.

But the important thing about all this is that the symptoms happen in some people precisely from this immunological reaction: runny nose, cough, fever and sore throat are, at the same time, attempts to eliminate the virus from the body and an effect of so many cells working in incessant way.

You can check the list of the most frequent Covid symptoms in this report, recently published by BBC News Brasil:

But how long do the discomforts persist? This timeframe can fluctuate considerably.

“It depends a lot on each individual. There are people with few symptoms who, after four or five days, are already recovered. In others, the same situation takes longer to pass”, replies infectious disease specialist and virologist Nancy Bellei, a professor at the Sao Paulo.

“Overall, the tendency is for worse symptoms, such as sore throat and fever, to last about three days”, estimates the specialist, who is also a member of the Brazilian Society of Infectious Diseases (SBI).

“After this period, it is normal for milder manifestations, such as a runny nose and cough, to persist for seven to ten days”, he concludes.

At this stage, it is important to stay in isolation and restrict contact with others as much as possible.

From an individual point of view, resting and staying well hydrated is essential to ensure a good recovery and give “a chance” for the body to react well. Taking some simple remedies for the annoyances of the infection, such as fever and pain, can also help.

“If after 72 hours of the onset of symptoms you are short of breath or fever persists, you need to seek medical attention,” suggests Bellei.

This message is even more important for those who may suffer from more serious Covid paintings, such as the elderly, those with chronic diseases and patients with a compromised immune system.

From a collective point of view, remaining in isolation is essential to cut the chains of transmission of the virus in the community and stop the rise of cases.

By staying at home and, if you need to go out, wearing a good quality mask, you are less likely to pass on Sars-CoV-2 through those droplets and aerosols mentioned earlier.

You can see how many days of isolation are needed in each situation in the following article:

Day 15 onwards: resolution (or onset of lasting symptoms)

Up to two weeks have passed since contact with the coronavirus, the immune system usually “wins the battle” and interrupts that process of replication and destruction of cells most of the time.

This victory, of course, is facilitated by vaccination — the doses make it possible to safely “train” defense units so that they know how to fight the pathogen even before they come into contact with it.

In some cases, unfortunately, the condition does not evolve that well: the virus manages to gain a lot of ground, reaches vital organs (such as the lungs) and generates a very serious inflammatory condition.

Generally, these situations require admission to the ICU (Intensive Care Unit) and intubation, in addition to increasing the risk of death.

And even in patients who have recovered well, there is a not inconsiderable risk of the long Covid, marked by discomfort that lasts for months (or even years).

While this area is still surrounded by many uncertainties, the US Centers for Disease Control and Prevention (CDC) estimates that up to 13.3% of people with Covid have long-lasting symptoms for a month or more. About 2.5% report problems for at least three months.

According to the institution, more than 30% of patients with Covid who were hospitalized still feel some discomfort after six months, ranging from tiredness and difficulty breathing to anxiety and joint pain.

The CDC points out that it “is working to understand more about these post-Covid experiences and why they happen, including why some groups are disproportionately affected.”

– This text was originally published in https://www.bbc.com/portuguese/geral-62002188