When discussing influenza viruses, one of the main concerns for scientists is the possibility of new viruses emerging, capable of causing global pandemics.

Despite constant monitoring by a global surveillance network, predicting when a new pandemic with global impact will occur and stopping its spread remains a challenge.

Researchers at the Oswaldo Cruz Institute (IOC/Fiocruz) clarify the conditions that can lead to a new pandemic episode, address measures that can minimize the impacts of a virus with this profile, and highlight the advances achieved by countries.

On June 11, 2009, the World Health Organization (WHO) declared an influenza pandemic due to the large-scale impact caused by a strain of the A(H1N1) virus.

The episode, which at the time became known as 'swine flu', led to the death of between 151 and 575 people worldwide, according to a study published by researchers from the Centers for Disease Control and Prevention (CDC) in the scientific journal The Lancet Infectious Diseases in 2012.

A national reference center for laboratory diagnosis of the Influenza virus, affiliated with the Ministry of Health, the Respiratory Virus and Measles Laboratory of IOC part of the WHO Global Influenza Surveillance and Response System.

To understand how influenza pandemics arise, the starting point is the observation that the influenza virus undergoes frequent mutations. Therefore, there is a repertoire of flu virus variations already in circulation.

The dynamics involving these viruses are quite predictable: through sneezing, coughing, and contamination of hands and surfaces, they spread. They are in constant circulation, with waves gaining momentum each winter, and can cause manifestations of varying severity.

Virologist Marilda Siqueira, head of the Respiratory Virus and Measles Laboratory at IOCHe explains that influenza pandemics occur when a new viral strain emerges from rearrangements in the virus's genome.

“Faced with this new variation of the virus, the set of antibodies in people who have already been in contact with other Influenza viruses that existed before is ineffective. As a result of the combination of the characteristic of lack of immunity in people to the respiratory transmission route of influenza, which makes the rate of its spread very rapid and difficult to control, the new genetic variations of Influenza have the potential to spread throughout the world,” he explains.

The new microorganism can lead to a significant number of infections, the intensity of which can vary from severe to mild from one pandemic to another. The factors influencing this impact remain unknown.

The 'Spanish flu', the most impactful pandemic in recent times, which marked its centenary in 2018, caused between 20 and 40 million deaths worldwide, according to the WHO.

Origin of a pandemic

Surprisingly, the emergence of a pandemic of global proportions depends on microscopic structures within the influenza virus.

During infection, the immune system is affected by two proteins present on the surface of the Influenza A virus, called hemagglutinin and neuraminidase. Remember these letters: these proteins are so important to the infectivity of Influenza that the initials H and N are key to establishing the name by which each genetic variant of the virus is named.

There are at least 18 subtypes of hemagglutinins and 11 subtypes of neuraminidases described. The A(H3N2) virus, for example, contains hemagglutinin subtype 3 and neuraminidase subtype 2.

Pandemics arise when the genetic makeup of a virus changes. It is expected that, in the process of multiplication, the virus will produce identical copies of itself.

It is this battalion of copies, produced inside the cells, that ensures a virus thrives and spreads.

Genetic rearrangements occur when two (or more) variations of the Influenza virus infect and multiply within the same host cell.

With two (or more) simultaneous protagonists in the copying process, a rearrangement between genomes can give rise to a new genetic variety.

Just look at the case of the most recent influenza pandemic in 2009: in the work of reconstructing the virus's origin, scientists believe that the A(H1N1) virus arose from a rearrangement of the genome of two viruses that simultaneously infected pigs.

These mutations would have resulted in a strain capable of infecting people.

“The complexity involved in the mechanism of genetic rearrangement makes it virtually impossible to predict the emergence of the next pandemic. Therefore, it is essential to have a constant system of epidemiological and laboratory surveillance, to detect the first cases early, provide clinical treatment, and have an efficient hospital network,” Siqueira points out.

Given this scenario, countries have national plans to deal with a possible influenza pandemic. In the case of Brazil, the strategy includes general guidelines essential to the action of health services and presents necessary orientations in the face of an emergency situation.

The plan aims to reduce the impact in terms of morbidity and mortality, optimize existing resources through planning (which involves laboratory diagnosis and drug stocks, to name a few aspects), reduce socioeconomic impacts, and maintain the functioning of essential services in the country.

“The pandemic preparedness plan considers various scenarios involving variables regarding clinical presentation, the impact of infection, and other parameters that are analyzed and define actions, such as the closure of schools and airports and the cancellation of public events, for example,” Siqueira points out.

The expert, who participated in the development of the Brazilian plan, adds that the speed in sharing scientific data is fundamental to ensuring an adequate public health response.

"Making the genetic data that characterize the variant of the virus with pandemic potential available as soon as it is detected is crucial for the plan to be put into action effectively. The population's role is to follow the strategy recommended by the Ministry of Health," he summarizes.

Lessons from the 2009 pandemic

Since 2009, the WHO, together with the countries that are part of the Global Influenza Surveillance and Response System, has been undertaking a series of measures aimed at improving strategies for a new pandemic event.

“There is a global movement in terms of organizing working groups, holding scientific meetings, and advising countries. The influenza virus is covered in several international treaties due to the harmful potential of a future pandemic, both in terms of health and economic and social impacts,” says Siqueira.

In May 2019, in a concerted effort to strengthen influenza virus surveillance, the IOC hosted an international course dedicated to genetic sequencing techniques. The initiative is a joint effort between the Institute, the Pan American Health Organization (PAHO) and the CDC, with a direct impact on the formulation of vaccines used to fight the flu. Experts from ten countries in the Americas participated in training on the F campusiocruz, in Rio de Janeiro.

In 2016 the IOC hosted the course 'Laboratory surveillance: selection, processing and sending of samples for diagnosing influenza and other respiratory viruses', promoted by PAHO, with support from the Ministry of Health. The following year, PAHO brought some 25 specialists from the Americas, including Bolivia, Costa Rica, Guatemala, Haiti and the Dominican Republic, to the country for a international course on molecular diagnosis of the Influenza virus. The training carried out at the Respiratory Virus and Measles Laboratory of IOC was the result of a partnership between the Institute and the CDC.

Siqueira points out that the Ministry of Health has been investing heavily in improving influenza control in Brazil.

"There has been an increase in the number of sentinel units that, since 2009, have started to consider Severe Acute Respiratory Syndrome (SARS), which are cases of hospitalized patients or those in the ICU, in addition to Influenza-like Illness (ILI), which is the mild form of the disease," he says.

The network of sentinel units, distributed across health services in all states, combined with a network of reference laboratories, including the Respiratory Virus and Measles Laboratory of IOC, allows monitoring of the circulation of the Influenza virus in the country by the folder. The improvement of influenza control systems was perceived homogeneously in the Americas, evaluates Siqueira. She points out that there is a strong perception, on the part of governments, of the importance of well-structured surveillance, and that countries have adhered to the protocols proposed by PAHO.

In 1918, one of the biggest influenza pandemics of recent times devastated Europe and reached several countries, including Brazil. The Spanish flu, as it became known, killed between 20 and 40 million people, according to WHO estimates. Other pandemics emerged in the world, with less severity, among them the Asian flu (1957), caused by the Influenza A (H2N2) virus, and the Hong Kong flu (1968), caused by the Influenza A (H3N2) strain.

performance of IOC

Since the detection of the first cases and the global alert by the WHO, the IOC It mobilized to receive samples. The actions of the Respiratory Virus and Measles Laboratory focused on the laboratory diagnosis of suspected cases and the training of health professionals to carry out the procedures.

Researchers from IOC They were responsible for the first genetic sequences of the pandemic Influenza A (H1N1) virus mapped in Brazil.

The study was conducted using samples from three patients, two from Rio de Janeiro and one from Minas Gerais, all diagnosed at the Laboratory. The information was deposited in the genetic information bank of the National Center for Biotechnology Information (NCBI), based at the National Institutes of Health (NIH) in the United States, in May 2009.

“Genetic sequencing is fundamental for monitoring the evolution of the virus and an important tool for the development of diagnostic protocols. The study contributed to strengthening collaboration with the international scientific community, which was essential for facing the pandemic”, clarifies Fernando Motta, researcher at the Laboratory, who participated in the investigations.

The researcher points out that, due to the large number of samples received, the team worked continuously to carry out the diagnoses, including holidays and weekends.

To ensure continuity of service, the Laboratory of IOC offered training so that technicians from Central Public Health Laboratories (LACENs) could carry out the diagnosis in their respective states of origin.

“The training in real-time RT-PCR, a methodology considered the gold standard for detection, allowed us to achieve, in record time, the decentralization of the influenza diagnosis protocol among the states that are part of our network. This was only possible due to the effort required to respond to the pandemic,” he emphasizes.

In 2009, the Laboratory performed approximately 17 sample diagnoses using real-time PCR. According to Fernando, after the pandemic, the protocol used for detecting the pandemic virus was adapted to identify other strains, including H3N2 and Influenza B.

Currently, the Laboratory of Respiratory Virus and Measles of IOC It receives samples from various sentinel units linked to the Ministry of Health for analysis, which contributes to the monitoring and surveillance of influenza in the country.

Among the studies developed are phylogenetic analyses, which allow for the evaluation of the evolutionary relationship between different influenza groups, the identification of variant strains of viruses that circulate during seasonal epidemics, the assessment of resistance levels to the antiviral oseltamivir, the response to vaccination, and surveillance for the possible emergence of new respiratory infection agents.