Pollen exposure can increase the risk of developing COVID-19 and is not just a problem for people with allergies, according to new research published on March 9th. Plant physiologist Lewis Ziska, co-author of the new peer-reviewed study and other recent research on pollen and climate change, explains the findings and why pollen seasons are longer and more intense.
What has pollen got to do with a virus?
The most important implication of our new study is that pollen may be a factor exacerbating COVID-19.
A couple of years ago, my co-authors demonstrated that pollen can suppress the response of the human immune system to viruses. By interfering with proteins that signal antiviral responses in the cells that line the airways, it can leave people more susceptible to a range of respiratory viruses, such as the flu virus and other SARS viruses.
In this study, we specifically examined COVID-19. We wanted to see how the number of new infections changed with increasing and decreasing pollen levels in 31 countries around the world. We found that, on average, approximately 44 percent of the variability in COVID-19 case rates was related to pollen exposure, often in synergy with humidity and temperature.
Infection rates tend to increase four days after a high pollen count. If there was no local blockage, the infection rate increased by about 4 percent for every 100 pollen grains in a cubic meter of air. A strict blockade halved the increase.
This exposure to pollen is not just a problem for people with hay fever. It is a reaction to pollen in general. Even the types of pollen that do not normally cause allergic reactions were correlated with an increase in COVID-19 infections.
What precautions can people take?
On days with a high pollen count, try to stay indoors to minimize exposure.
When outdoors, wear a mask during pollen season. Pollen grains are large enough for almost any mask designed for allergies to work to keep them out. However, if you sneeze and cough, use an effective coronavirus mask. If you are asymptomatic with COVID-19, all this sneezing increases your chances of catching the virus. Mild cases of COVID-19 can also be confused with allergies.
Why does the pollen season last?
As the climate changes, we see three things that are specifically related to pollen.
One is the beginning of the pollen season. Spring changes start earlier and there are signs worldwide of pollen exposure early in the season.
Second, the general pollen season lengthens. The time you are exposed to pollen, from spring, mainly driven by tree pollen, to summer, which is weeds and grasses, and then autumn, which is mainly the ambrosia, now about 20 days ago was in 1990. As you move towards the poles, where temperatures rise more rapidly, we found that the season is even more pronounced.
Third, more pollen is produced. Colleagues and I described the three changes in an article published in February.
As climate change increases pollen count, this could result in greater human susceptibility to viruses.
These changes in the pollen season have been underway for several decades. When my colleagues and I looked back at as many different pollen conservation records as we could locate since the 1970s, we found solid evidence to suggest that these changes have been occurring for at least the last 30 to 40 years. .
Concentrations of greenhouse gases increase and the Earth’s surface heats up and this will affect life as we know it. I have been studying climate change for 30 years. It is so endemic to the current environment that it will be difficult to examine any medical problem without at least trying to understand whether climate change has already affected it or will.
Lewis Ziska is an associate professor of environmental health sciences at Columbia University.