Pollen can increase your risk of contracting COVID-19

Exposure to pollen can increase your risk of developing COVID-19, and it’s not just a problem for people with allergies, according to new research published on March 9. 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 explains why pollen seasons are getting longer and more intense.

What does pollen have to do with a virus?

The most important finding of our new study is that pollen may be a factor in exacerbating COVID-19.

A few years ago, my co-authors showed that pollen could suppress the reaction of the human immune system to viruses. By interfering with proteins that signal antiviral responses in cells that line the airways, it can make people more susceptible to a host of respiratory viruses, like 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 evolves with the rise and fall of pollen levels in 31 countries around the world. We found that on average, about 44% of the variability in COVID-19 case rates was related to exposure to pollen, often in synergy with humidity and temperature.

Infection rates tended to increase four days after high pollen counts. If there was no local lockdown, the infection rate increased on average by about 4 percent per 100 pollen grains in one cubic meter of air. Strict lockdown halved the increase.

This exposure to pollen is not only a problem for people with hay fever. It is a reaction to pollen in general. Even the types of pollen that usually don’t cause allergic reactions were correlated with an increase in COVID-19 infections.

What precautions can people take?

On days when the pollen count is high, try to stay indoors to keep your exposure as low as possible.

When you are outdoors, wear a mask during pollen season. The pollen grains are large enough that almost all masks designed for allergies work to keep them out. However, if you sneeze and cough, wear an effective coronavirus mask. If you’re asymptomatic with COVID-19, all of that sneezing increases your chances of spreading the virus. Mild cases of COVID-19 could also be mistaken for allergies.

Why does the pollen season last longer?

As the climate changes, we see three things that relate specifically to pollen.

One is an earlier start to the pollen season. Spring changes start earlier and there are overall signals of pollen exposure earlier in the season.

Second, the overall pollen season is lengthening. The time you are exposed to pollen, from spring, which is mostly tree pollen, to summer, which is weeds and grasses, and then fall, which is mostly ragweed, is about 20 more days in North America now than it was in 1990. As you move towards the poles, where temperatures are rising faster, we have found the season to become even more pronounced.

Third, more pollen is produced. My colleagues and I described the three changes in an article published in February.

As climate change increases the number of pollens, this could lead to greater human susceptibility to viruses.

These changes in the pollen season have been going on for several decades. When my colleagues and I looked at as many different pollen conservation records as we could find since the 1970s, we found strong evidence to suggest that these changes have been happening for at least 30 to 40 years.

Greenhouse gas concentrations are increasing and the Earth’s surface is warming, which will affect life as we know it. I have been studying climate change for 30 years. It’s so endemic to the current environment that it’s going to be difficult to look into a medical problem without at least trying to understand if climate change has already affected it or will.

Lewis Ziska is Associate Professor of Environmental Health Sciences at Columbia University.