Episode #7 - Serological surveys

Transcript

Vismita: Hello and welcome to Science in 5, WHO’s conversations in science. Today, we are talking to WHO’s Chief Scientist, Dr Soumya Swaminathan, about serological studies. Welcome, Soumya.

Soumya: Thank you, Vismita. 

Vismita: Soumya, tell us why do public health authorities do serological surveys? 

Soumya: So, maybe we can start with what are serological surveys. These are basically tests, blood tests, that you do in people to look at antibodies against the SARS-CoV-2 virus and it's usually done in a population group.

So what it tells you is a couple of things. The first thing is it tells you how many people in that group, in that population have been exposed to the virus, have had an infection. Because we know now that many infections occur without any symptoms and people may not have sought care or they may not have had a test done at all. And so, the true number of people who've been infected in a community can only be known when you do these kinds of serological surveys. So, that's the first piece of information you'll get. The second is you can also start looking at which groups are more exposed or have had higher rates of infection. So, if you include health care workers, if you include children, if you include, you know, other kinds of frontline workers, the elderly, you start getting an idea of who is more exposed, who's been less exposed, where have the infections being the most.

You can also look at, you know, the localities within cities. So for example, you could look at low income, highly crowded, urban settlements versus rural areas, for example, to see if there's a difference in exposure. And then finally, if you do these tests repeatedly, these surveys repeatedly over a period of time, the authorities, the local public health authorities get an idea of how infection rates are progressing in that particular area. Are they still increasing? Have they stabilised, et cetera?

And finally, we could also use this opportunity to test the same group of people over a period of time to understand more about the immunity against this virus because one of the things, you know, that everyone wants to know is if you've been infected and you have antibodies, how long do they last? How long do they protect you? And here's an opportunity to also answer that question. 

Vismita: Soumya, a lot of these sero surveys have been done across the world. What have we learned about this new disease COVID-19?

Soumya: So, there have been several of these done. I think we know of at least a hundred sero surveys done in countries around the world and some of the data that started coming out is very interesting because the first lesson we've learned is that a much larger proportion of people actually had the infection than were detected by testing, especially in the early days. And this varies from, you know, 5 to 10 to even 40 times more people in some cities have been exposed to the virus. So, it's been much more widespread.

The second thing we've learned is that, in most places, which have had big outbreaks in North America, in Europe, in Asia, the data coming out shows that only about 5 to 10% of the population in those places, even where they had big outbreaks, actually have antibodies. So, that's telling us that the majority of people in most countries around the world are still susceptible to this virus and they can still get the infection if they are exposed.

And then it's also telling us, you know, what's happening over time. There have been some cities which have repeated serological testing at weekly or monthly intervals and have been able to track the progress of their epidemics.

Vismita: Soumya, as public health experts learn from these serological surveys, there's so many data points that come out, it can get a little confusing. What are the questions that the public should ask? And what is the data that the public should look for when such a survey comes out? 

Soumya: Yes, I think this is a really important because the public needs to understand what does it mean for me? So, I think it helps to inform you as to how big the outbreak has been in your town or city, how effective have been the control measures. It will bring home to people when they know that only 5% or only 10% of people in their city actually have been exposed and have antibodies. 

And then over a period of time, of course, they can also see how the measures that have been put in place, you know, what the measures that the government is doing as well as how well the public is responding and behaving in a responsible manner, if that's actually having an impact in keeping the infection rates under control.  

Vismita: Thank you, Soumya. That was WHO’s Chief Scientist, Dr Soumya Swaminathan, explaining serological surveys. Until next time then. Stay safe and stick with science.

Speaker key

Vismita   Vismita Gupta-Smith

Soumya  Dr Soumya Swaminathan