What do you need to know:
– After studying the characteristics of SARS-CoV-2 and other respiratory viruses, researchers indicated that Covid-19 can become a seasonal disease
– This means that, even with an effective vaccine, the new coronavirus can continue to circulate at certain times of the year, especially in temperate regions. This will require constant care with distance and hygiene measures
– If this is the case, to prevent new outbreaks, annual immunization campaigns will be necessary, as is already the case with the common flu
– Despite this prediction, scientists warn that, so far, the virus is not controlled anywhere in the world and continues to spread in both hot and cold climates.
Covid-19 could become a seasonal illness like the flu, indicates a study published last week in the journal Frontiers in Public Health. According to researchers, when the disease stops spreading at a pandemic rate – that is, when the population reaches herd immunity -, SARS-CoV-2 should continue to cause outbreaks at certain times of the year, especially in countries with climate seasoned. Professor Hassan Zaraket, from the American University of Beirut, Lebanon, one of the authors of the study, indicates that the population “will need to learn to live with this and continue to practice the best preventive measures, including the use of masks, physical distance and hygiene of the hands ”.
The authors’ prediction lowers the hope of those who imagine getting rid of Covid-19 with the arrival of a vaccine. Many believe that, when herd immunity is achieved, the virus stops circulating. Only it is not always so.
THE concept of collective immunity or herd means that if a significant portion of the population develops antibodies against a particular disease – whether due to the large number of infected people or through mass vaccination -, the chain of transmission of the pathogen is interrupted. This can occur, however, permanently or temporarily, depending on the characteristics of the virus and the human organism. The rate of mutation of the pathogen can be so high that it is no longer recognized by the defense system of those who have been infected. In addition, the duration of immunity is not always permanent against a given pathogen. In the case of the new coronavirus, these two issues are not yet fully clarified by science.
As research on immunity against SARS-CoV-2 they take different paths. While some indicate that the number of antibodies decreases dramatically after a few months of infection, others point out that T cells, another important component of the immune system, can remain active for years in the body. Scientists indicate that mutation rate that SARS-CoV-2 suffered is high, but do not believe that, at least until now, it has already caused significant changes in the pathogen to the point of becoming unrecognizable to those who have already been infected. There is a risk, however, that this will happen in the future.
Vaccination can be annual
Despite doubts about these issues, analyzes of the behavior of the new coronavirus in different countries led the researchers responsible for the article in Frontiers in Public Health indicating that he must develop a seasonal pattern. To reach these conclusions, the group of scientists carried out a review of articles on the seasonality of other respiratory viruses and compared them with the characteristics already discovered of SARS-CoV-2. Influenza viruses, which cause some types of flu, and several coronaviruses responsible for the common cold are known, for example, to peak in winter in temperate regions, but circulate throughout the year in tropical regions.
To this day, science still does not know exactly what causes some viruses to behave seasonally, but it is already agreed that some factors are essential to this pattern. One of them, according to the study’s authors, is that many respiratory viruses are more stable and remain longer in the air in environments with cold temperatures and low humidity. Add to that the behavior of people, who tend to crowd more indoors during the cold. This set of elements makes an environment more conducive to the spread of the virus.
An article recently published in the journal Aerosol and Air Quality Research suggests that indoor environments with low humidity are more conducive to the spread of the new coronavirus, since viral particles are able to stay afloat longer in the air. According to this research, there is evidence that, in regions of temperate climate – further away from the tropics -, the transmission of Sars-CoV-2 was more intense in winter.
Although there is no scientific consensus, this may be an indication that lower temperatures and a dry climate may favor contagion. If that is the case and if, over time (due to virus mutations or decreased immunity), an already infected person becomes susceptible to the new coronavirus again, an effective vaccine will be able to reduce transmission and death rates as much as possible, but only if that product is available for mass immunization annually, as with common flu. Until then, however, the researchers warn that the new coronavirus continues to spread in all climates intensely and, in no region, protective measures should be neglected.
Contagion rate remains high
As the percentage of people with immunity against SARS-CoV-2 in the world is still small, it still has a much higher transmission rate than other respiratory viruses. The “basic reproduction number”, called R0, shows the number of people that an infected individual can infect. In common flu, the R0 is 1.3 – that is, each person can pass the disease to up to 1.3 people on average. The degree of contagion of the new coronavirus varies between an R0 of 2.2 and 3.8, according to different studies. According to Lebanese researchers, it is for this reason that the virus continues to spread in different regions of the planet, regardless of the climatic condition.
They believe that the rate of transmission should stabilize once the pandemic is controlled. “R0 is expected to drop substantially, making the virus more susceptible to seasonal factors”, indicate the authors. At the conclusion of the research, they point out that SARS-CoV-2 remains a new virus and, despite the speed of scientific discoveries, there are still unknown aspects. “Whether our predictions will be confirmed or not, that will still be seen in the future. But we think it’s highly likely, given what we know so far, that Covid-19 will eventually become seasonal, as [acontece com] other coronaviruses, ”they say.
Frontiers in Public Health
Annals Of Internal Medicine. Article available at:
COVID-19 Genomics UK (COG-UK) consortium. Information available at:
Aerosol and Air Quality Research. Article available at:
Edited by: Marcela Duarte and Maurício Moraes