World Health Organization officials on Tuesday walked back the comments below that were made on Monday after drawing criticism from epidemiologists across the world. Dr. Maria Van Kerkhove, head of the WHO’s emerging diseases and zoonosis unit, said Tuesday that asymptomatic spread is a “really complex question” and much is still unknown. “We don’t actually have that answer yet,” she said.
“I was responding to a question at the press conference. I wasn’t stating a policy of WHO or anything like that. I was just trying to articulate what we know,” she said on a live Q&A streamed across multiple social media platforms. “And in that, I used the phrase ‘very rare,’ and I think that that’s misunderstanding to state that asymptomatic transmission globally is very rare. I was referring to a small subset of studies.”
Coronavirus patients without symptoms aren’t driving the spread of the virus, World Health Organization officials said Monday, casting doubt on concerns by some researchers that the disease could be difficult to contain due to asymptomatic infections.
Preliminary evidence from the earliest outbreaks indicated that the virus could spread from person-to-person contact, even if the carrier never develops symptoms. But WHO officials now say that while asymptomatic spread can occur, it is not the main way it’s being transmitted.
“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,” Dr. Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, said at a news briefing from the United Nations agency’s Geneva headquarters. “It’s very rare.”
The virus is primarily spread via respiratory droplets when someone coughs or sneezes or if they touch a contaminated surface, scientists say.
Asymptomatic transmission is particularly worrisome for public health officials, leading many to institute severe lockdowns and policies requiring masks in public. That’s because those patients never develop symptoms and, in many cases, don’t even know they are infected. WHO officials say Covid-19 can also spread in the so-called pre-symptomatic stage — a few days before a patient shows symptoms.
The clarification comes after the WHO’s original comments incited strong pushback from outside public health experts, who suggested the agency had erred, or at least miscommunicated, when it said people who didn’t show symptoms were unlikely to spread the virus.
Maria Van Kerkhove, the WHO’s technical lead on the Covid-19 pandemic, made it very clear Tuesday that the actual rates of asymptomatic transmission aren’t yet known.
She added: “We are constantly looking at this data and we’re trying to get more information from countries to truly answer this question.”
To some, it came across as if the WHO was suggesting that people without symptoms weren’t driving spread. Some studies, however, have estimated that people without symptoms (whether truly asymptomatic or presymptomatic) could be responsible for up to half of the spread, which is why the virus has been so difficult to contain. Isolating people who are sick, for example, does not prevent the possibility they already passed the virus on to others. Some modeling studies have assumed quite widespread asymptomatic transmission.
“The WHO created confusion yesterday when it reported that asymptomatic patients rarely spread the disease,” an email from the Harvard Global Health Institute said Tuesday. “All of the best evidence suggests that people without symptoms can and do readily spread SARS-CoV-2, the virus that causes Covid-19. In fact, some evidence suggests that people may be most infectious in the days before they become symptomatic — that is, in the presymptomatic phase when they feel well, have no symptoms, but may be shedding substantial amounts of virus.”