Pollen exposure can increase your risk of developing COVID-19, and it’s not just a problem for people with allergies, according to new research released March 9. Plant physiologist Lewis Ziska, a co-author of the new peer-reviewed study and other recent research on pollen and climate change, explains the findings and explains why pollen seasons are getting longer and more intense.
What has pollen to do with a virus?
The main tradeoff from our new study is that pollen may be a factor in worsening COVID-19.
A few years ago, my co-authors showed that pollen can suppress the human immune system’s response to viruses. By interfering with proteins that signal antiviral responses in cells lining the airways, it can make people more susceptible to potentially a whole host of respiratory viruses, such as the flu virus and other SARS viruses.
In this study, we looked specifically at COVID-19. We wanted to see how the number of new infections changed with the rise and fall of pollen levels in 31 countries around the world. We found that, on average, about 44 percent of the variability in COVID-19 cases was related to pollen exposure, often in synergy with humidity and temperature.
Infection rates usually increased four days after a high pollen count. If there was no local lockdown, the contamination rate increased by an average of about 4 percent per 100 pollen grains in a cubic meter of air. A strict lockdown cut the rise in half.
This exposure to pollen isn’t just a problem for people with hay fever. It’s a response to pollen in general. Even pollen types that do not usually 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 your exposure.
Wear a mask when you are outside during the pollen season. Pollen grains are so big that almost any mask designed for allergies will work to keep them out. However, if you sneeze and cough, wear a mask that is effective against the coronavirus. If you’re asymptomatic with COVID-19, all that sneezing increases your chances of spreading the virus. Mild cases of COVID-19 can also be mistaken for allergies.
Why is the pollen season taking longer?
As the climate changes, we see three things specifically related to pollen.
One of these is an earlier start to the pollen season. Spring changes begin earlier and there are worldwide signs of pollen exposure earlier in the season.
Second, the general pollen season is getting longer. The time you are exposed to pollen, from spring, which is mainly powered by tree pollen, to summer, which consists of weeds and grasses, and fall, which is mainly ragweed, is now about 20 days longer in North America than it was in 1990. As you head towards the poles, where temperatures are rising faster, we found that the season is getting even more pronounced.
Third, more pollen is produced. Colleagues and I described all three changes in an article published in February.
As climate change is pushing up pollen counts, it could potentially increase human susceptibility to viruses.
These pollen season changes have been going on for decades. When my colleagues and I looked back at as much different pollen keeping data as we could find since the 1970s, we found solid evidence to suggest that these shifts have been happening for at least the past 30 to 40 years.
Greenhouse gas concentrations are rising and the Earth’s surface is warming, and that will affect life as we know it. I’ve been studying climate change for 30 years. It is so endemic to the current environment that it will become difficult to look at a medical problem without at least trying to understand whether climate change has already affected it or will do it.
Lewis Ziska is an associate professor of environmental health sciences at Columbia University.