The more sun, the less chance corona has to spread. According to new research from the Open University in Heerlen, this is due to three factors: solar radiation, immune response due to hay fever and higher temperatures.
A factor that actually ensures faster spread of corona is called ‘mobility to indoor recreation locations’. That means, for example, sitting in bars instead of on terraces and, for example, going to indoor playgrounds.
“With those four factors together, 87.5 percent of the reproduction of the virus can be explained,” says lead researcher Martijn Hoogeveen. By reproduction he means the speed at which the virus is spread. For example, the more powerful the solar radiation, the slower the spread.
Herd immunity less important for spread
At the same time, that high percentage of 87.5 percent means that herd immunity has no decisive influence on the speed of the virus’s spread. “It does have a very important influence, because vaccination makes the disease a lot milder and a hospital visit is often not necessary,” says Hoogeveen.
Several studies, which we have previously published, endorse this. As it turned out: the delta variant causes vaccinated people to become infected more often, but they are somewhat less contagious than non-vaccinated people.
Seasonal Effect Factors
The coronavirus will become endemic, is the widely held opinion. That means we have to live with it for the rest of our lives. And according to Hoogeveen and his researchers, the virus will behave approximately the same as the flu virus, which revives every year in the autumn. In spite of the pricks.
In that case, the number of infections decreases in the spring, due to the above factors. But how exactly do they work? We’ll go through them one by one.
1. Solar radiation
There are multiple ways in which solar radiation helps reduce virus transmission. UV light breaks down the virus, for example, and our immune system is strengthened by the production of melatonin through solar radiation. Vitamin D from sunlight may also help. “Although that reasoning is not completely uncontroversial,” says Hoogeveen.
2. Hay fever
A striking factor for corona reduction is hay fever. The pollen in the air seems to trigger an immune system response. “And that response just happens to be useful against covid or the flu.”
The rising temperature has an indirect effect. It is not the case that the virus dies in warm weather, but because of higher temperatures we are more often in places where the risk of infection is lower. “It turns out that it doesn’t matter very much whether it is busy in those places,” says Hoogeveen. According to this research, a busier park or forest is not a riskier place to contract the virus.
4. Indoor mobility
It works the other way, of course. Where mobility outside does not cause infections, it does when we move inside. The ‘party peak’ in the summer showed this well. If we move in en masse, corona will have more chance. “But that doesn’t apply to home,” says Hoogeveen. “Then you infect your housemates, but that’s it.”
Stronger decline due to seasonal effect
Due to the seasonal effect, corona infections can fall by 25 to 70 percent, says Hoogeveen. So if the infections are high at the end of winter, that means a significant decline after the start of spring.
Hoogeveen’s research is by no means an argument for not getting vaccinated, because in many cases this prevents a severe course of the disease. “But the intriguing thing about the research is that herd immunity is not so important for the spread. Coronaviruses can always come back and people can contract multiple covid infections.”
And so we will continue to hear about corona for years and years to come. But especially in the fall.