Episode #67 - Understanding immunity

25 February 2022 | Science conversation

Vismita Gupta-Smith

We are talking about how our body develops immunity when it encounters a new virus like SARS-CoV-2, which causes COVID-19. Hello and welcome to Science in 5, I'm Vismita Gupta-Smith. We are talking to Dr. Soumya Swaminathan, WHO's Chief Scientist. Welcome, Soumya. Soumya, explain to us how the body develops immunity when it encounters a new virus like SARS-CoV-2.

Dr. Soumya Swaminathan

So our immune system is actually amazing. It's versatile, but it's also complex. And when the body is exposed to a new virus like the SARS-CoV-2 virus, which it's never seen before, the immune system does get activated and there are many things which start happening. The first and the most rapid response is the production of antibodies. And this is also accompanied by messages that are being sent to other parts of the immune system so that the T-cells or the cell mediated immune response is also activated. And ultimately, what happens is that if the body's immune response is strong, it's able to overcome the virus and eliminate the infection. But also, it develops a memory response so that the next time the body sees the same virus, it's able to respond much more quickly because the memory cells, both memory B cells and T cells in the body are able to recognize and respond. So we all talk about antibodies all the time. It's one part of the immune system, but it's a much larger and much more complex system which keeps us healthy and, you know, gives us the ability to respond to a lot of infections.

Vismita Gupta-Smith

So, Soumya, you explained that SARS-CoV-2 was a new virus. We did not have immunity to it as human beings. But now at this stage of the pandemic, we also have vaccines. Explain to us how vaccines help to develop immunity.

Dr. Soumya Swaminathan

So the way vaccines work, and they are an amazing, amazing innovation of the 20th century, is by mimicking the organism, the virus or the bacteria. And so the spike protein of the SARS-CoV-2 virus is taken and made into a vaccine. Of course, we know there are different types of vaccines mRNA, the virus vectored vaccines inactivated, but they all do the same thing, and that's present in a safe way the antigen of the SARS-CoV-2 to the body. And so the immune response that's generated is very similar to the immune response to a natural infection. But of course, the vaccines are a safer way of stimulating the immune system.

Vismita Gupta-Smith

So Soumya, if I've been infected, do I still need the vaccine?

Dr. Soumya Swaminathan

So natural infection does stimulate the immune response and gives you some immunity, but it varies from person to person. So if you've had a very mild infection, the immune response may be actually quite low than those who've had a severe infection and we don't know exactly how long it will last. In some people, it lasts a few months. In some people, it goes to a year. So the advantage of getting vaccinated, even if you have had prior infection, is that you're really boosting that immune system and ensuring that your immune system will have a good memory to this virus so that it has a very good response if you get exposed in the future, particularly to new variants with new mutations. So hybrid immunity, which is both natural and vaccinated, is the best kind of immunity to have.

Vismita Gupta-Smith

Soumya, explain to us why it's important to still keep observing these protective measures like masks, physical distancing, opening doors and windows to circulate air, not going into crowds, washing hands. Why is that still important if we have a vaccine, if many people have already been infected and may have some level of immunity?

Dr. Soumya Swaminathan

So we're still learning a lot about the immunity to this virus, and what we know now is that people who have had the infection in the past and certainly those who have been vaccinated or both have good immune responses which protect you from getting sick even if you get infected. The current vaccines that we have today are very effective at preventing people from getting severely ill and ending up in the hospital, but are not 100% effective against infection. So even if you are vaccinated, you can still get the infection, which means you are infectious, you can pass it on to others, even though hopefully you're not going to be severely ill yourself. Also, we've seen with the variants that are emerging and especially with the latest Omicron variant of concern that it was able to overcome the immunity and therefore it was able to infect a lot of people who actually had previous infection or who'd been vaccinated. Luckily, because of their immunity, they didn't get ill, but they still were infected. And that's why it's important to continue to mask and to continue to observe the other public health measures, particularly if there's a lot of virus still circulating in your community.

Vismita Gupta-Smith

Thank you, Soumya. That was Science in 5 today. Until next time then. Stay safe, stay healthy and stick with science.