Even though there is no longer a public health emergency due to the pandemic, many of my friends, neighbors, and relatives are still experiencing COVID-19 episodes.
Earlier last summer, while camping, a relative contracted COVID-19. There was a sick neighbor of mine. One person showed no symptoms, but remained silent as a vivid pink line emerged on their test strip every morning. We and the dogs thrilled at the reunion as he shouted updates across the street while we walked our dogs: “The line was a little fainter today,” “It’s gone,” and ultimately, “It’s been two days since the line disappeared.”
Reports began to come in again in the fall and winter: coworkers who contracted the coronavirus; the sick neighbor’s family who contracted COVID-19 long after he recovered; a friend who became ill after seeing a relative and missed Christmas with her parents; the cousins of another friend who tested positive shortly after celebrating the holidays.
The highs and lows of contagion observed in the US and other temperate regions of the world are reflected in the experiences of the people in my circle. All of this made me wonder if the coronavirus that causes COVID-19, SARS-CoV-2, will ever become a virus that mainly affects people during the cold and flu seasons. The timing and creation of vaccines would be simplified by a known season. It might also persuade people that wearing a mask during specific seasons of the year is a prudent precaution.
Based on some recent research, it appears that COVID-19 may be a year-round issue for the time being, mostly caused by immunity levels and human activity rather than weather trends.
COVID-19 is a weather-resistant spreader.
In cold, dry conditions, several common respiratory infections proliferate more readily (SN: 1/11/23). Similar to flu viruses, SARS-CoV-2 has greater stability in low temperature and humidity environments. Yet according to Vincent Munster, a virologist at the Rocky Mountain Laboratories in Hamilton, Mont., a portion of the United States, scientists didn’t certain whether the virus’s stability in carefully regulated lab circumstances translated to improved transmission at particular times of year in the real world. The National Institutes of Health.
Hamsters were used in experiments by Munster and associates as human proxies. The predominant mechanism of COVID-19 transmission is airborne transmission, and the researchers wanted to study this method without having to worry about other, less likely modes of transmission such huge droplets or contaminated surfaces. In order to contain the infection, the team infected one hamster and placed it 90 cm apart from a cage containing an uninfected hamster. Only airborne viruses may potentially infect the uninfected hamster at such distance.
The researchers examined a comfortable 45 percent relative humidity and a standard climate-controlled room temperature of 22° Celsius, or roughly 72° Fahrenheit. In tests, other hamsters were kept at 10° C, which is colder than fall and winter in many regions of the world. The third group of animals received the tropical treatment, with a temperature of 27°C and 65% relative humidity.
As per the researchers’ paper published in npj Viruses on January 9, airborne transmission of the coronavirus remains unaffected by such environmental circumstances. The virus propagated amongst hamsters in all studied circumstances at comparable rates.
Because these viruses are airborne for brief periods of time, Munster claims that the environmental impact on them is typically minimal. Instead of speaking in hours or days, he speaks in seconds to minutes.
Although studies by Munster and colleagues have demonstrated that aerosols can linger in the air for hours, he believes that infection most likely occurs much more quickly. An infectious virus is typically exhaled by an infected individual, whereupon it is inhaled by someone in close proximity. In those situations, there is simply not enough transit time for environmental factors to significantly affect the transmission of the virus.
“Does that mean these viruses don’t have the propensity to become seasonal?” was the researchers’ main question, according to Munster.He believes that although the calendar won’t be the deciding factor, the coronavirus might have a season at some point. Rather, he believes that human behavior and people’s immunity to the virus—whether from vaccination, past infections, or both—will dictate when COVID season begins.
Strangers are not the ones who pose a risk of transmission.
That element of human behavior is the subject of another recent study. Data from a smartphone app that alerted users when they had been in contact with someone who tested positive for COVID-19 was examined by Oxford University researchers. Over 7 million alerts were analyzed by the team between April 2021 and February 2022, when the study was conducted. The goal of the study was to determine whether the proximity of an individual to an infected person and the length of time that the ill and well were together could be used to reliably predict the risk of contracting COVID-19.
Epidemiologist Christophe Fraser notes that contrary to popular belief, the greatest risk of contracting an infection is not from “stranger danger.”
For fifteen minutes, the app was programmed to alert users if they had been within two meters of an infected person. At that point, “the risk of transmission was really quite low,” he claims. Fraser et al. reported in Nature on December 20 that the probability of transmission increased by 1.1 percent every hour of exposure and continued to rise over several days. Although they constituted only 6% of interactions, households were responsible for 40% of transmissions.
There were many encounters, but few infections, due to quick, casual interactions with strangers, such those that occur at the grocery store. Rather, “someone you’ve spent a lot of time with: You could have dinner with them, go to the movies with them, or you live at home with them or you work next to them in an office” is the one who poses the greatest risk, he claims. This is due to the fact that infected individuals continuously breathe out the virus, and the longer you are exposed to the virus and the closer you are to the source, the higher your risk of contracting it.
In addition to the weather, Fraser adds human activity also affects the seasons of other respiratory viruses. For example, following summer and winter breaks, students return to school around the time of flu and respiratory syncytial virus (RSV) outbreaks (SN: 8/12/21). It might take decades for COVID-19 to follow a similar trend, he speculates.
Seasonal viruses can also be suppressed by human behavior, at least temporarily: in 2020 and 2021, the number of flu and RSV infections was significantly reduced by social separation, mask wear, and other COVID-prevention measures (SN: 2/2/21). However, as soon as those limitations were removed, the viruses returned.
Researchers believe that some of the seasonal virus return is due to a decline in collective immunity, particularly in young infants who are immunological-naive and older adults whose immune systems are generally weakened. Additionally, immunity decreases with distance from an infection or booster dose.
Future COVID-19 seasonality may be mostly caused by shifts in human immunity, according to Luca Ferretti, Fraser’s Oxford colleague. However, as far, it has not transpired.
Almost anyone might become infected with the virus early in the pandemic because nobody was resistant to it. The immune system was able to halt or slow the initial strain of the virus after vaccinations were made available and a large number of people developed immunity via shots or prior infections.
COVID-19 may already be a seasonal sickness if the coronavirus mutated like other respiratory viruses do, albeit more slowly. However, the coronavirus is evolving quickly, frequently in ways that enable it to evade immune system defenses and infect people who have previously had immunity.
For example, the JN.1 variety first surfaced in the United States. reports released in October by the Centers for Disease Control and Prevention. It accounted for over 86% of cases in the US as of January 20. In just the week of January 7–13, about 30,000 people were hospitalized due to the illness.
The largest coronavirus outbreaks to date have been caused by newly discovered virus variations including delta and omicron, which enable the virus to evade antibodies. Nobody is certain that the virus still possesses such brilliant escape maneuvers in its repertoire.
We now have different immunity when we are most contagious.
Human immunity has altered not only to shield us from COVID-19 but also to alter the peak infectious periods of individuals. People were most contagious and produced the most virus in the early stages of the pandemic, often even before symptoms appeared. Researchers reported on September 28 in Clinical Infectious Diseases that the peak of viral generation has now been pushed out until roughly four days after symptoms start due to immunity from vaccinations and prior COVID-19 infections.
According to Nira Pollock, a clinical diagnostics specialist at Boston Children’s Hospital, the immune system is combating the virus early in the infection and causing symptoms before viral replication truly takes off, which explains the difference.
That is advantageous. However, it may also unintentionally result in an increase in infections since it can influence the timing of positive results from home tests. Producing enough virus for the test to detect is necessary to get a positive line on a home test. It is therefore possible to have a negative test result yet still have COVID-19 and be able to infect others if there is a delay in the peak viral output. For this reason, if you experience symptoms or have come into contact with someone who does, you should get tested again.
According to Pollock, “you are not done if you test negative on day one.” The FDA advises repeat testing “if you continue to be symptomatic, because it’s possible that your highest viral load will be on your fourth day of symptoms, or on your third or fifth.” It is stated on the packaging.
It would be convenient to be able to designate COVID-19 season on a calendar. Then at least we would know if we should wear masks with our beachwear or only with our hats, gloves, and mittens. Plus, there wouldn’t be as much speculation about when to give immunizations.
For the time being, however, the coronavirus follows its own unpredictable schedule. It may ultimately become a seasonal virus, depending on our actions. We might someday force it into seasonal subordination with the strength of our combined immune systems and our resolve to take preventative measures to avoid infecting others.
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