In this roundup of the latest research into the covid-19 pandemic, we cover encouraging evidence for immunity, why the virus may not be very airborne, and an unexpected effect of the pandemic on our weather forecasts.
A study out this week seems to offer a ray of sunlight amidst concerns that immunity to the coronavirus may be short-lasting.
The preliminary study, released on the preprint server medRxiv on Friday, analysed the antibody responses of people who had mild to moderate covid-19 and were treated in New York City, the location of the single deadliest outbreak recorded in the U.S. so far (at least 22,000 deaths).
In more than 90% of people who tested positive for covid-19 antibodies, the researchers found, there was a robust level of neutralising antibodies, the antibodies thought to be most important in preventing a second infection. The presence of these neutralising antibodies remained stable at least three months post-recovery.
Neutralising antibodies are often a key indicator of immunity, so this is a good sign that covid-19 immunity for most people should last for at least the near future. Other research has also shown that a second form of immune response, led by T cells, is robust following a bout of covid-19. But we still have to be vigilant and track survivors to know if and when immunity may start to wane.
The evidence for droplet transmission
Earlier this month, the World Health Organisation acknowledged that covid-19 can be spread through tiny aerosols breathed out by infected people, not just through larger droplets — in other words, that it can be an airborne disease.
Today, the World Health Organisation formally announced a change in its stance over very two important issues concerning covid-19. The organisation stated that people can spread the virus while asymptomatic and that airborne transmission of the virus is possible under certain circumstances, such as crowded rooms with little ventilation.Read more
An enduring question, however, is whether aerosol transmission is playing a significant role in spreading the pandemic compared to droplet transmission (both involve breathing germs, so face masks are helpful in either scenario). Aerosols travel farther than droplets after being exhaled, and when they dry up, they can leave behind particles of gunk that linger in the air, possibly for hours. If aerosols are commonly spreading covid-19, then precautions like staying 1.83 m away from others and wearing cloth or surgical masks might not be enough to reduce risk in many situations.
A new preliminary study this week could offer some relief there. It analysed data that tracked health care workers in real time during their interactions with covid-19 patients. About 2% per cent were diagnosed with covid-19 during the study period. The authors then ran models that tried to estimate how well certain known airborne germs, such as tuberculosis, would have spread in the same scenario.
These models are routinely used to estimate the airborne potential of an infectious disease, depending on factors like viral load, people’s level of exposure to an infected person, and the ventilation of the room. The real-time data allowed researchers to know where, how often, and for how long health care workers were spending time with patients. They also ran several simulations to account for which masks people were assumed to be using (either surgical masks or n95 respirators, which are much better at preventing airborne transmission) as well as varying levels of ventilation in a room.
They ultimately concluded that the airborne transmission rate of SARS-CoV-2 was likely far lower than it was for tuberculosis, rhinovirus, and even the original SARS.
Though the study’s findings haven’t gone through peer review, it lines up with other research suggesting that covid-19 is opportunistically airborne and that most cases can still be explained by droplet transmission. And it should mean mask-wearing and distancing will remain crucial ways to stay safe. That said, the authors also concluded that the “risk of infection is substantially reduced with increased ventilation of rooms,” meaning that there are important steps we can take to lower the chances of covid-19 spreading via aerosols.
It’s mucking up our weather forecasts
With fewer planes in the air because of covid-19, the accuracy of weather forecasts has declined, according to a new study out Friday.
Weather forecasting relies partly on data provided by aircrafts criss-crossing the world, since planes regularly record information about atmospheric conditions like wind, temperature, and humidity during their flights. But the pandemic led to severe travel restrictions between countries, while tourism obviously took a sharp plunge.
UK scientist Ying Chen, a senior research associate at the Lancaster Environment Centre, looked at weather forecasts across the world between March and May 2020. He found they were less accurate than previous years in places that planes frequently travel over, such as North America, southeast China, and Australia. They got even worse for remote regions and for longer-term forecasts. He also estimated that the world lost 50-75% of its aircraft weather observations during those months.
This drop in accuracy is manageable in the short term, and the forecasting of precipitation remained steady, since models can still use satellite data to figure that out. But the longer it takes to get accuracy back up, the more chance it could handicap the “early warning of extreme weather and cause additional economic damage on top of that from the pandemic,” Chen wrote.
Forecasts in some areas, like Western Europe, were largely unaffected by the loss of aeroplanes, however, likely because they have an abundance of ground weather stations that can pick up the pace.
“It’s a good lesson which tells us we should introduce more observation sites, especially in the regions with sparse data observations,” Chen said in a statement released by the American Geophysical Union. “This will help us to buffer the impacts of this kind of global emergency in the future.”