WEBVTT - Understanding Silent Spreaders 0:00:06.640 --> 0:00:11.760 Welcome to Prognosis. I'm Laura Carlson. It's day nine one 0:00:12.119 --> 0:00:16.640 since coronavirus was declared a global pandemic. Our main story. 0:00:17.680 --> 0:00:22.160 A top World Health Organization official sparked a controversy earlier 0:00:22.200 --> 0:00:27.160 this week over comments regarding asymptomatic carriers of COVID nineteen. 0:00:28.480 --> 0:00:32.879 She first said instances of asymptomatic carriers spreading the virus 0:00:33.000 --> 0:00:39.879 are very rare, before later clarifying her remarks. We explore 0:00:40.000 --> 0:00:43.080 why some people don't get sick after they're infected with 0:00:43.120 --> 0:00:46.320 the virus and why their role in its spread is 0:00:46.400 --> 0:01:00.280 still unclear. But first, here's what happened today. The World 0:01:00.320 --> 0:01:03.560 Health Organization said today that a persistent increase in cases 0:01:03.600 --> 0:01:07.920 in Latin America is of deep concern as hospitals across 0:01:07.920 --> 0:01:12.639 the region come under increasing strain. This comes one day 0:01:12.680 --> 0:01:17.640 after Anthony Fauci, the US government's top infectious disease expert, 0:01:18.000 --> 0:01:22.640 said the pandemic is far from over. China is offering 0:01:22.640 --> 0:01:26.399 employees of some large state run companies the option to 0:01:26.480 --> 0:01:31.480 be inoculated with two vaccines currently in development. The government 0:01:31.480 --> 0:01:34.440 would only hand out the vaccine to workers intending to 0:01:34.520 --> 0:01:40.640 travel overseas. The European Union plans a gradual and partial 0:01:40.680 --> 0:01:43.320 easing of a ban on most travel to the block 0:01:43.800 --> 0:01:49.560 beginning July one. In May, the price of whitebread dropped 0:01:49.720 --> 0:01:53.560 the most since World War Two. That's according to the 0:01:53.600 --> 0:01:58.800 Bureau of Labor Statistics. Dress prices and car insurance fell 0:01:58.920 --> 0:02:02.880 by the most on Kurt. Months of quarantine. It appears, 0:02:03.080 --> 0:02:06.920 have turned stay at home Americans into home bakers and 0:02:07.040 --> 0:02:11.520 lowered demand for anything but casual clothing as weakness across 0:02:11.639 --> 0:02:16.440 most categories pushed the overall consumer price index lower for 0:02:16.480 --> 0:02:28.120 a third month and now our main story. A comment 0:02:28.200 --> 0:02:31.240 by a w h O official earlier this week caught 0:02:31.280 --> 0:02:35.120 many health experts off guard. She threw doubt on what 0:02:35.200 --> 0:02:39.800 has been accepted for months. Silent spreaders, carriers of the 0:02:39.840 --> 0:02:44.520 coronavirus who don't show symptoms readily transmit the disease to others. 0:02:45.560 --> 0:02:49.919 The official later clarified her comments, But just how risky 0:02:50.160 --> 0:02:56.480 are these asymptomatic carriers? Bloomberg Senior editor Jason Gale helps 0:02:56.600 --> 0:03:06.639 us untangle the issue. Back in February, the Diamond Princess 0:03:06.639 --> 0:03:09.520 cruise ship was the center of an explosive outbreak of 0:03:09.560 --> 0:03:13.200 the coronavirus when it was quarantined in Japan. Of some 0:03:13.280 --> 0:03:16.120 three thousand, seven hundred and eleven passengers and crew on 0:03:16.240 --> 0:03:19.919 board the luxury ship, almost a fifth caught it at 0:03:19.960 --> 0:03:23.720 the time of testing. Surprisingly, most of those infected didn't 0:03:23.720 --> 0:03:27.880 have fever, dry cough, or difficulty breathing, the usual symptoms 0:03:27.880 --> 0:03:32.000 of COVID nineteen, and when doctors followed those asymptomatic cases 0:03:32.040 --> 0:03:35.360 for weeks, they found that just under half never developed 0:03:35.400 --> 0:03:39.920 any disease. That contradicted initial findings from the World Health Organization. 0:03:40.600 --> 0:03:44.400 The agency said in March that asymptomatic infections are rare, 0:03:45.120 --> 0:03:47.920 but since then reports from around the world have shown 0:03:47.920 --> 0:03:52.240 that asymptomatic cases aren't swer rare, and in some instances 0:03:52.600 --> 0:04:00.800 they might be the source of infections. The majority of 0:04:00.840 --> 0:04:02.960 transmission that we know about is that people who have 0:04:03.040 --> 0:04:06.240 symptoms transmit the virus to other people through infectious ruplets. 0:04:06.760 --> 0:04:10.480 That's Maria van Kirkhoff, the whose technical lead on COVID nineteen, 0:04:10.840 --> 0:04:14.120 speaking during a Facebook live event in Geneva on Tuesday. 0:04:14.520 --> 0:04:16.960 She was clarifying comments she made earlier in the week 0:04:17.279 --> 0:04:19.520 about the risk of the virus spreading from people who 0:04:19.560 --> 0:04:22.440 don't have symptoms. We do know that some people who 0:04:22.480 --> 0:04:25.200 are asymptomatic. Are some people who don't have symptoms can 0:04:25.240 --> 0:04:28.640 transmit the virus on and so what we need to 0:04:28.680 --> 0:04:31.599 better understand is how many of the people in the 0:04:31.600 --> 0:04:34.920 population don't have symptoms, and separately, how many of those 0:04:34.960 --> 0:04:46.040 individuals go on to transmit to others. The extent to 0:04:46.120 --> 0:04:51.200 which these silent carriers may also be silent spreaders isn't clear, 0:04:51.600 --> 0:04:54.680 and it probably varies between groups of people because the 0:04:54.720 --> 0:04:59.160 fact is, like age, genetics, underlying medical conditions, and people's 0:04:59.240 --> 0:05:04.000 individual and une responses, Uncertainty over how the virus behaves 0:05:04.040 --> 0:05:07.960 has hindered nation's efforts to reopen bantered economies. If there 0:05:08.000 --> 0:05:10.679 are a lot of people in the community sharing crowded 0:05:10.720 --> 0:05:14.279 subway trains who don't know they're infected, well that's a 0:05:14.279 --> 0:05:18.359 big problem if they're also contagious. Dr Peter colign On, 0:05:18.600 --> 0:05:21.599 professor of medicine at the Australian National University in Canberra, 0:05:21.920 --> 0:05:26.880 says it's less likely individuals without respiratory symptoms will spread 0:05:26.880 --> 0:05:29.760 the virus simply because they're not coughing and spluttering on 0:05:29.839 --> 0:05:34.240 other people. I actually do think asymptomatics cause less infection 0:05:34.279 --> 0:05:37.240 than symptomatics, maybe because they're not sneezing or coughing as 0:05:37.279 --> 0:05:39.880 much and therefore they're not spreading droplets as much. Is 0:05:39.920 --> 0:05:43.039 there's a few studies that show that of cases are 0:05:43.120 --> 0:05:47.680 due to people so super spreaders, but that still leaves 0:05:47.680 --> 0:05:51.400 who are dcovers for Since infected people without symptoms aren't 0:05:51.400 --> 0:05:54.880 in bed nursing their illness, they are typically more mobile, 0:05:55.080 --> 0:05:58.680 which does present an infection risk. A simple nose rub 0:05:58.720 --> 0:06:01.520 could transfer virus party calls to a hand that could 0:06:01.560 --> 0:06:04.320 then touch a doorknob or a force it which someone 0:06:04.360 --> 0:06:06.800 else might touch and then rub their eye or mouth, 0:06:06.880 --> 0:06:12.080 inoculating themselves and causing an infection. So we've got to 0:06:12.080 --> 0:06:16.080 actually assume that people with minimum symptoms are still a 0:06:16.200 --> 0:06:18.720 risk for having the virus and being able to spread it. 0:06:19.320 --> 0:06:22.599 And that actually means that's good news in the community 0:06:22.640 --> 0:06:24.360 because it means we can keep on doing a whole 0:06:24.400 --> 0:06:28.080 lot of things within limits. But we've got to just 0:06:28.200 --> 0:06:31.400 assume it's there at low levels and therefore take all 0:06:31.440 --> 0:06:33.640 the precautions we have to not let us spread. So 0:06:33.720 --> 0:06:36.719 the hand hygiene, the physical distancing don't go to work 0:06:36.760 --> 0:06:39.520 if you've got any symptoms, et cetera. That decreases the risk, 0:06:39.560 --> 0:06:42.640 but it doesn't make the risk of zero. Peter says 0:06:42.680 --> 0:06:45.920 that in countries where the coronavirus is spreading out of control, 0:06:46.360 --> 0:06:50.200 it makes sense for public health officials to target symptomatic cases, 0:06:50.600 --> 0:06:53.040 isolate them and trace who they have been in contact 0:06:53.080 --> 0:06:56.760 with the monitor for further spread. But in countries where 0:06:56.760 --> 0:06:59.840 there is little or no obvious transmission going on, it 0:07:00.000 --> 0:07:03.160 is important to hunt down all infections. I think the 0:07:03.200 --> 0:07:06.280 asymptomatics are still important, particularly if you want to get 0:07:06.360 --> 0:07:09.640 levels of virus at very low levels of transmission. I mean, 0:07:09.680 --> 0:07:12.600 if you're in a country where it's out of control, okay, yeah, 0:07:12.760 --> 0:07:15.520 concentrate on the symptomatics. I don't have a problem with that. 0:07:15.880 --> 0:07:18.920 But if you're in a situation like Career in New 0:07:19.000 --> 0:07:23.640 Zealand Australia, the the asymptomatics are also important to find 0:07:24.440 --> 0:07:27.400 um and once Europe gets down to low levels, that's 0:07:27.440 --> 0:07:30.080 going to be equally important because otherwise you find next 0:07:30.080 --> 0:07:37.080 winter you're back in the same problem again. Infected people 0:07:37.120 --> 0:07:40.120 can also spread the virus via droplets that come out 0:07:40.160 --> 0:07:43.600 of them mouths in ways that don't require coffee. Dr 0:07:43.640 --> 0:07:46.480 SONJ Sent and I care An infectious diseases. Physician in 0:07:46.520 --> 0:07:49.640 Canberra says that could be important as communities come out 0:07:49.640 --> 0:07:52.880 of lockdown, especially in the context of large gatherings like 0:07:53.000 --> 0:07:57.400 protest marches. There may be certain scenarios where an asymptomatic 0:07:57.440 --> 0:08:03.760 person maybe create eating more droplets or perhaps even aerosolizing 0:08:03.760 --> 0:08:06.440 a bit. For example, in a choir practice. We've had 0:08:06.640 --> 0:08:11.600 outbreaks in acquire setting in a loud nightclub where you 0:08:11.680 --> 0:08:14.800 have to shout a lot, or a protest or or 0:08:14.880 --> 0:08:18.600 some other event where someone won't be speaking normally. They 0:08:18.680 --> 0:08:22.760 might be therefore generating more droplets, and in that situation 0:08:22.800 --> 0:08:26.040 in a symptomatic person might be able to spread to 0:08:26.720 --> 0:08:29.760 someone else that way. So j I agrees that the 0:08:29.880 --> 0:08:33.360 likelihood of onward transmission is lower in a person without 0:08:33.480 --> 0:08:37.679 respiratory symptoms compared with someone who's coughing. Problem is, there 0:08:37.679 --> 0:08:40.240 are a lot of people who are infected without symptoms, 0:08:40.600 --> 0:08:43.240 and there sheer number alone amplifies the risk of some 0:08:43.320 --> 0:08:48.160 transmission occurring. There are a lot of asymptomatic infections out 0:08:48.200 --> 0:08:52.600 there and will only work out that proportion ultimately when 0:08:52.640 --> 0:08:56.600 we have a good antibody test, So good zero surveys 0:08:56.679 --> 0:09:00.080 will will give us that answer, And of course it 0:09:00.200 --> 0:09:04.520 is kind of hard because is someone truly asymptomatic if 0:09:04.559 --> 0:09:07.560 they're feeling a little bit under the weather, or are 0:09:07.600 --> 0:09:12.240 they actually symptomatic. So there are those those slight subtleties 0:09:12.280 --> 0:09:15.640 in definition we have to think about. Jia says, the 0:09:15.720 --> 0:09:19.960 prospect that asymptomatically infected people are less likely to spread 0:09:19.960 --> 0:09:23.720 the virus doesn't mean we should abolish physical distancing and 0:09:23.760 --> 0:09:27.040 other measures to control the pandemic. Not now, not until 0:09:27.040 --> 0:09:28.760 we get a vaccine. I think we have to be 0:09:28.840 --> 0:09:32.440 very careful about that. Low risk is not no risk, 0:09:33.280 --> 0:09:35.719 and we've seen the consequences of what can happen if 0:09:35.720 --> 0:09:39.880 there is a super spreader event. Uh, it has all 0:09:39.880 --> 0:09:46.160 the downstream effects, the impact on our health system, our economy, socially, 0:09:46.679 --> 0:09:50.720 it's just a disaster. So we have to be very 0:09:50.840 --> 0:09:56.280 very careful. But still except that asymptomatic transmission is lower risk, 0:09:56.720 --> 0:10:00.160 but it is still not no risk. The coronavirus US 0:10:00.320 --> 0:10:03.720 has a way of exploiting our vulnerabilities when we allow 0:10:03.760 --> 0:10:08.200 it to spread. Undetected cases can snowball quickly. The only 0:10:08.280 --> 0:10:11.360 sure fireway to counter it is to limit its ability 0:10:11.400 --> 0:10:14.880 to infect others. As the w A chose said on Tuesday, 0:10:15.280 --> 0:10:19.200 in the absence of a vaccine, testing, quarantining and contact 0:10:19.200 --> 0:10:36.080 tracing remain our best defense against this insidious disease. That 0:10:36.160 --> 0:10:39.800 was Jason Gale, and that's our show today. For coverage 0:10:39.840 --> 0:10:43.280 of the outbreak from one bureaus around the world, visit 0:10:43.320 --> 0:10:48.160 bloomberg dot com slash coronavirus and if you like the show, 0:10:48.640 --> 0:10:51.560 please leave us a review and a rating on Apple 0:10:51.640 --> 0:10:55.079 Podcasts or Spotify. It's the best way to help more 0:10:55.160 --> 0:11:00.120 listeners find our global reporting. The Prognosis Daily edition is 0:11:00.120 --> 0:11:05.280 produced by Topher Foreheads Jordan Gaspure, Magnus Hendrikson and me 0:11:05.880 --> 0:11:10.280 Laura Carlson. Today's main story was reported by Jason Gale. 0:11:11.120 --> 0:11:15.760 Original music by Leo Sedrin. Our editors are Francesco Levi 0:11:16.040 --> 0:11:20.680 and Rick Shine. Francesco Levi is Bloomberg's head of podcasts. 0:11:21.240 --> 0:11:22.120 Thanks for listening.