When outdoor risk is lowest
Walking your dog, riding a bike, hiking on a trail or picnicking with members of your household or vaccinated friends are all activities where the risk for virus exposure is negligible. In these kinds of situations, you can keep a mask on hand in your pocket, in case you find yourself in a crowd or need to go indoors.
- On April 13, 2021, U.S. health agencies called for an immediate pause in the use of Johnson & Johnson’s single-dose Covid-19 vaccine after six recipients in the United States developed a rare disorder involving blood clots within one to three weeks of vaccination.
- All 50 states, Washington, D.C. and Puerto Rico temporarily halted or recommended providers pause the use of the vaccine. The U.S. military, federally run vaccination sites and a host of private companies, including CVS, Walgreens, Rite Aid, Walmart and Publix, also paused the injections.
- Fewer than one in a million Johnson & Johnson vaccinations are now under investigation. If there is indeed a risk of blood clots from the vaccine — which has yet to be determined — that risk is extremely low. The risk of getting Covid-19 in the United States is far higher.
- The pause could complicate the nation’s vaccination efforts at a time when many states are confronting a surge in new cases and seeking to address vaccine hesitancy.
- Johnson & Johnson had also decided to delay the rollout of its vaccine in Europe amid concerns over rare blood clots, but it later decided to resume its campaign after the European Union’s drug regulator said a warning label should be added. South Africa, devastated by a more contagious virus variant that emerged there, suspended use of the vaccine, and Australia announced it would not purchase any doses.
“I think it’s a bit too much to ask people to put the mask on when they go out for a walk or jogging or cycling,” said Dr. Muge Cevik, a clinical lecturer of infectious disease and medical virology at the University of St. Andrews School of Medicine in Scotland, where outdoor masking has never been required. “We’re in a different stage of the pandemic. I think outdoor masks should not have been mandated at all. It’s not where the infection and transmission occurs.”
“Let me go for my run, maskless. Mask in pocket,” tweeted Dr. Nahid Bhadelia, an infectious diseases physician and the medical director of the special pathogens unit at Boston Medical Center. “Given how conservative I have been on my opinions all year, this should tell you how low risk is, in general, for outdoors transmission for contact over short periods — and lower still after vaccination. Keep the masks on you for when you are stationary in a crowd and headed indoors.”
To understand just how low the risk of outdoor transmission is, researchers in Italy used mathematical models to calculate the amount of time it would take for a person to become infected outdoors in Milan. They imagined a grim scenario in which 10 percent of the population was infected with Covid-19. Their calculations showed that if a person avoided crowds, it would take, on average, 31.5 days of continuous outdoor exposure to inhale a dose of virus sufficient to transmit infection.
“The results are that this risk is negligible in outdoor air if crowds and direct contact among people are avoided,” said Daniele Contini, senior author of the study and an aerosol scientist at the Institute of Atmospheric Sciences and Climate in Lecce, Italy.
Even as more-infectious virus variants circulate, the physics of viral transmission outdoors haven’t changed, and the risk of getting infected outdoors is still low, say virus experts. Pay attention to the rates of infection in your community. If case counts are surging, your risk of encountering an infected person goes up.
When outdoor fun moves indoors
Dr. Cevik notes that debates about outdoor masking and articles showing photos of crowded beaches during the pandemic have left people with the wrong impression that parks and beaches are unsafe, and distracted from the much higher risks of indoor transmission. Often it’s the indoor activities associated with outdoor fun — like traveling unmasked in a subway or car to go hiking, or dropping into a pub after spending time at the beach — that pose the highest risk. “People hold barbecues outdoors, but then they spend time indoors chatting in the kitchen,” said Dr. Cevik.