PHILADELPHIA - Pennsylvania is at the beginning of a fall COVID-19 surge, the state's health secretary said Wednesday, matching experts' predictions that cooler weather will worsen the coronavirus' spread.
That's likely both because of biology and behavior, though scientists say the latter may matter more.
"As it gets colder, people spend more time indoors and that will increase their risk of exposure to the virus," said Nate Wardle, a spokesperson for the department of health.
Health Secretary Rachel Levine noted that around the country, small gatherings tend to be driving case count increases, "and I feel like we're seeing that in Pennsylvania," she said Wednesday.
The choices people make in fall and winter - whether to meet indoors, continue to wear masks, or maintain distance - are likely going to be the biggest determinants of how serious a cold weather surge could be, according to a Princeton study released in September but not yet peer reviewed, said Rachel Baker, postdoctoral research associate at the Princeton Environmental Institute and the study's lead author.
"Indoor gatherings are going to be higher risk," she said, due to indoor air being more stagnant than air outside. "If we think the virus can be partly airborne then being indoors you sort of trap it."
Baker believes the newness of this virus also means seasonal changes that normally decrease viral spread are less impactful. Human immune systems have no familiarity with COVID-19, she said, which might be why summer, typically a less friendly environment for viruses, didn't squelch the pandemic. The study notes the virus has spread effectively in environments ranging from India's monsoon season to winter in Wuhan.
Baker's study, which focused on New York City, also found that the level of immunity people acquire after recovering from COVID-19 will also matter in how the virus spreads this winter, particularly in areas that were hit hard this spring.
Any effect climate may have on the virus' rate of transmission is, "something we're only going to be able to tease out after we've seen one full year of spread of SARS-CoV-2," said Stephen Kessler, a research fellow in the department of immunology and infectious diseases at Harvard T.H. Chan School of Public Health, in a conference call Wednesday.
In fact, the reasons climate affects any viruses are not completely understood. Generally, researchers believe temperature and humidity play roles in how well the virus can survive in the air, and thus make its way into your body.