Why Do Some Viruses Have a Seasonal Cycle?

by Gertrud U. Rey

Have you ever wondered why some viruses circulate primarily in the winter and others are more prevalent in the summer? Although we don’t have a clear answer to this question, a combination of factors is likely responsible.  

Work done in the field of respiratory viruses suggests that these viruses can be transmitted in four ways: 1) through direct contact with an infected person; 2) through indirect contact by touching an inanimate object contaminated by an infected person; 3) through inhalation of large virus-containing droplets that drifted over a short distance; and 4) through inhalation of small virus-containing droplets that drifted over a long distance (i.e., “airborne” transmission). The same body of work also indicates that the seasonality of viral transmission is likely driven by changes in the environment, changes in human physiology, and changes in human behavior, all of which affect the stability and spread of viruses.

One of the environmental elements that influences the viability of respiratory viruses is UV light, which increases in intensity in the summer and typically inactivates viruses. Studies have also shown that the viral envelope, the outermost layer of many respiratory viruses, is more stable in cool weather and more likely to break down in warm temperatures. However, the biggest environmental contributors to the seasonal nature of respiratory viruses are temperature and absolute humidity. Absolute humidity is a measure of the exact amount of water vapor in a certain volume of air (expressed as grams of water per cubic meter of air) and it is independent of temperature. This feature distinguishes absolute humidity from relative humidity, which is a ratio (expressed as a percentage) of the absolute humidity to the amount of water vapor that can exist in the air at its current temperature. When the air is hot and absolute humidity is high, expelled respiratory droplets tend to sink to the ground or settle on nearby inanimate objects. In contrast, cool dry air causes droplets to partially evaporate and form smaller aerosol particles that remain suspended longer, float further, and are thus more likely to be inhaled by another person. Seasonal changes in absolute humidity, marked by high levels in the summer and low levels in the winter, both indoors and outdoors, are opposite to the seasonal patterns of circulation of influenza viruses, coronaviruses, and respiratory syncytial virus, which peak in the winter and drop in the summer. This inverse correlation suggests that absolute humidity is a key player in the overall transmission of these viruses.

However, the correlation between absolute humidity and incidence of infection does not explain the circulation of respiratory virus infections in tropical regions, where it occurs continuously, even though both indoor and outdoor absolute humidity remain high year-round. The most likely explanation for this disparity is that transmission in these regions occurs mainly through direct and/or indirect contact between individuals. The high absolute humidity probably causes expelled droplets to settle on nearby surfaces, where they evaporate less water than they would under dry conditions, thereby causing any viral particles they contain to remain stable until they are taken up by the next person.

Changes in human physiology may also alter the rate of infection, susceptibility, and severity of disease. Shorter winter days lead to low levels of vitamin D and melatonin, both of which are generated through a cascade of enzymatic reactions that require exposure to sunlight. This deficiency compromises certain innate immune responses like macrophage activation, which in turn decreases an individual’s ability to fight a viral infection.

Seasonal changes are also marked by changes in human behavior, which may further impact the frequency of contact between infected and uninfected individuals. In the winter, people spend more time indoors, where viral transmission is more likely as they come into close contact with infected individuals. The start of the school year also typically coincides with an increase in the incidence of respiratory infections among children, which is then often followed by transmission to their family members.

Meanwhile, many viruses that spread by the fecal-oral route predominate in the summer. There are various reasons for this phenomenon. Prior to rollout of the poliovirus vaccines, poliovirus infections often occurred in the summer, because children and adults would gather at picnics where they consumed cold, uncooked foods, which, compared to cooked foods, are more likely to be contaminated with viable stool-derived viruses. Many outbreaks also originated at public swimming pools containing inadequately treated water. Likewise, enteroviruses like hand, foot, and mouth disease virus also circulate more during the summer, but the reason why is less clear. It is possible that an interference mechanism between viruses, where infection by a first virus reduces the likelihood of infection by another virus, causes one group of viruses to predominate during one season.   

You can obviously still become infected with a “winter” virus during the summer months, and vice versa. Washing your hands frequently is the most effective method for preventing infection with any virus, and based on what we know; using a humidifier in your home might lessen your chances of becoming infected with a respiratory virus.

[The seasonality of influenza virus was previously discussed here and here.]

3 thoughts on “Why Do Some Viruses Have a Seasonal Cycle?”

  1. This study goes into considerable detail in this subject, and provides a contour map of contagion risk along with quite a few other graphs and discussion, including aircraft profiles.

    Hanley BP, Borup B (2010) Aerosol influenza transmission risk contours: a study of humid tropics vs. winter temperate zone.

  2. Cinnamon (barks) is the antidote to vaccinations.

    Make immune lung honey yourself:
    In the spring, collect new buds from coniferous trees (spruce, fir, pine, etc.).
    and place them in blossom honey, cut into small pieces.
    Fill the jar halfway and then top up with honey.

    Medicine Oil:
    lots of dried, shredded thyme or oregano
    (for the immune system, lungs, strengthening against fatigue)
    and lots of Bio-Knobel (small) in olive oil with sea salt
    and shake/turn daily.
    2 spoonfuls with every meal daily.

    Medicinal dessert: yoghurt with honey/cane sugar and cinnamon.
    ————————————————– —————-


    preliminary remark:
    Viruses are allergic to cold (mint menthol),
    Heat (ginger causes heat, so does chili) and dryness (lack of water).
    Corona is not contagious, no more than flu, because it’s only in the blood.
    Immune mineral zinc: rice, chicken.

    5 general keys against all viruses:

    1. Hot substances: chili, hot peppers (its water or tea),
    Ginger, garlic, onion, horseradish, fruit acids: lemon
    2. Bitter substances: eucalyptus (antimalarial),
    Wormwood (Artemisia Annua = mugwort against Ebola), hops, cocoa, yarrow, roots (e.g. valerian)
    3. Yellow substances = flavonoids destroy virus genes:
    Turmeric, Vanilla, Ginger, Orange, Carrot, Black Tea, Apple, Onion, Honey, Coriander (Brainstem Infestation)
    4. Soap substances = saponins pack viruses: oats, linden blossoms, ginger, coffee, clove, turmeric.
    5. Blood counts:
    Red Dyes: Blackberry, Cherry, Elderberry, Blood Orange, Black Olive, Cocoa
    Green substances: oregano, thyme, mint (AIDS medicine), green tea,
    Rosemary (adrenal cortex helps immune system), vegetables (cabbage species)
    White substances for lymph blood: garlic, banana, onion, lemon,
    Ginger, rice, chamomile (anti-leukemia agent), milk (vitamin D essential), zinc (rice, chicken), egg white, horseradish

    Ginger possesses all of these 5 properties.

    Corona symptoms:
    Burning in the throat: These are viruses that dry out the skin with their suction cups.
    Countermeasure: immediately gargle with menthol mouthwash (or toothpaste).
    or eat a hot pepper (drink its water).
    Disorientation or disturbances of consciousness = brainstem attack,
    Antidote is coriander, also: horseradish.
    Loss of appetite: orange.

    Corona, SARS, flu (influenza)

    Natural remedy given by Mother Maria to Maria Esperanza in 2016 against:
    Colds, flu, sore throats, respiratory infections.
    There will be a flu-like disease that will cause the deaths of a great many.
    This disease will attack lungs and heart.

    ½ crushed larger garlic clove
    2 slices chopped ginger root (rather a bit more)
    1 tablespoon lemon juice
    1 teaspoon of honey

    Put the garlic and ginger in a mug.
    Add lemon juice and honey. Pour boiling hot water into the cup
    and let the mixture steep for at least 5 minutes.
    (DO NOT BOIL the mixture itself!)
    Drink every evening, about an hour before bedtime. Anyone who already has symptoms
    He should drink a full cup 3 times a day.
    If you don’t have fresh garlic, you can use a Knofi capsule as a substitute.
    Is there an aftertaste or bad breath because of the Knofis,
    then one should eat some sprigs of parsley.

    Blackberries and hawthorn also strengthen the immune system.

    Another important note:
    Drinking medicinal waters that arose during apparitions of the Mother of God
    (e.g. Lourdes, Heroldsbach, San Damiano, Medjugorje, Mercy Fountain of Mary, emergency spring, donkey fountain, etc.)
    raises and strengthens the human immune system in a special way.

    There are some references to this from the Middle Ages,
    that people who drank the water from the donkey well during the plague period survived the plague.

    Summary of all “Corona information”:
    Ginger is most effective (acts against fever condition similar to eucalyptus),
    also: cinnamon (yoghurt with honey), clove, lemon juice, eucalyptus products, mint, thyme,
    Conifers (also juniper berries):
    Spruce, fir, pine – collect numerous new buds in spring and soak them in honey.
    Cuisine: chicken or rice = zinc, fish: lung function,
    Garlic (acts like ginger) and onion, rosemary, turmeric, chili.
    Milk = vitamin D, honey = glucose (dextrose), oranges have the same effect as lemon (is more intense).
    Ginger and garlic specifically keep the head clear of viruses.
    Laurel Oil – Oregano Oil – Honey.

    Immune system related to the gut:
    Yoghurt, mint, organic garlic, thyme and flaxseed (added yoghurt)
    Pectin from apple or banana.
    Immune involvement of the adrenal cortex: rosemary.
    Lymph glands: onion, garlic, lemon.
    Lungs: Omega 3 (fish, vegetable oils) – fish for lung function,
    Orange, mint, thyme, anise, chamomile or yarrow (bronchi), cinnamon, garlic onion.
    Text-Image https://kath-zdw.ch/forum/index.php?action=dlattach;topic=558

  3. “Have you ever wondered why some viruses circulate primarily in the winter and others are more prevalent in the summer? Although we don’t have a clear answer to this question, a combination of factors is likely responsible.” – Gertrud

    Could it be because of atomic or sub-atomic factors (Chimera Detection – 3)?

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