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Coronavirus Explainers

One Of The Puzzles Of COVID-19 Is The Large Proportion Of People Who Are Asymptomatic: Dr Vincent Rajkumar Of Blood Cancer Journal

While most COVID-19 cases in India remain asymptomatic, here’s what Dr Vincent Rajkumar, editor-in-chief of Blood Cancer Journal thinks about the prevalence of asymptomatic coronavirus patients in India

One Of The Puzzle Of COVID-19 Is The Large Proportion Of People Who Are Asymptomatic: Dr Vincent Rajkumar of Blood Cancer Journal
  • 80 per cent of COVID-19 patients in India are asymptomatic: Study
  • Severity of COVID-19 could depend upon viral load: Dr Rajkumar
  • Exposure to coronaviruses in past may trigger immune response: Dr Rajkumar

New Delhi: India has crossed the 55 lakh mark in terms of the confirmed COVID-19 cases. As per an internal analysis by the Integrated Disease Surveillance Programme (IDSP), about 80 per cent of COVID-19 patients in India are asymptomatic. The large chunk of those infected being asymptomatic has not only made controlling this pandemic a challenge globally, it is also something that sets the SARS-CoV-2 apart from the other coronavirus outbreaks like Severe Acute Respiratory Disease (SARS) in 2002 and Middle East Respiratory Syndrome (MERS) in 2012.

Both these outbreaks were contained as only the people showing symptoms were at risk of transmitting the disease, which made isolating the infected cases easier.

NDTV speaks to Dr Vincent Rajkumar, editor-in-chief of Blood Cancer Journal and a cancer expert, to help us understand why are some people asymptomatic while others suffer from a serious bout of infection.

Also Read: Coronavirus Explainer: What Is COVAX Initiative?

NDTV: One of the biggest mystery in understanding the novel coronavirus remains – why do some patients get critically ill while most remain asymptomatic?

Dr Vincent Rajkumar: Yes, we do know that while some people suffering from COVID-19 are severely symptomatic – they need oxygen support, ICU, ventilators; while others are completely asymptomatic and then there’s a spectrum in between. One of the puzzles of COVID-19 is the large proportion of people who are asymptomatic.

I think there are four easy ways to look at it and these might be the main reasons for this. Firstly, some of us have innate ability to quickly clear the virus, so we hardly have any symptoms, it’s about immunity.

Another possibility is the viral load; if the exposure to the virus is a small amount of virus or a small dose that gives the system enough ability to clear the virus quickly before it becomes symptomatic. It gives a head-start to the immune system.

The third factor might be genetics – there are some studies that suggest that certain blood group types, certain polymorphisms, may explain why some people get much sicker than others.

And lastly, there is the issue of cross-reactive immunity. SARS-CoV-2 is a coronavirus and coronaviruses cause the common cold, so it is possible that a huge proportion of the population might be exposed to the various coronaviruses in the past not the same SARS-CoV-2 but others. And whatever immunity they have against that could play a cross-reactive role, could affect or target the new coronavirus as well, this is called cross-reactive immunity. it can be in the form of B cells or T cells. That might be protecting them from COVID-19.

These four reasons probably can help explain why some people are asymptomatic while some much more symptomatic.

Also Read: Nine Months Into The COVID-19 Pandemic, Which Vaccine Candidates Are In The Final Stages Of Trial? 

NDTV: Can you tell us more about T cells, they have been talked about a lot since the COVID-19 pandemic and there’s a lot of ongoing research on these.

Dr Vincent Rajkumar: Again the background is that when we get an infection, we usually amount both antibody responses, which is called a B cell response as well as T cell response. Both responses work together to help us fight most infections. And when you measure antibody levels, you’re only getting part of the picture, you’re finding out all of the people who have been exposed to SARS-CoV-2, who have developed antibodies. But what we are finding from many studies is that there’s an extra subset of people whom we’re not able to detect antibodies, maybe they already have T cells that are reactive to the SARS-CoV-2 virus.

Therefore, these T cells could also offer some protection that we are not recognising. The second factor is that they have looked at samples collected before COVID-19 came and you can detect these T cells that are reactive to SARS-CoV-2 virus even the samples that were collected way before the start of the pandemic. That means there must be some T cells that are cross reactive again, that was generated in response to some other virus but somehow, they seem to cross-react with the new virus.

And so we don’t understand how much protection the T cells will offer, I don’t think they’ll be enough to prevent you from getting the infection. But from what we have seen with young kids who have been vaccinated at six months with measles, that T cell response may be, by itself, enough to prevent at least severe disease.

Also Read: AstraZeneca Vaccine Trial Pause A ‘Wake-Up Call’, Says WHO

NDTV: India is now at a stage where it is adding nearly 1 lakh cases every day. What do you think about how India has dealt with the coronavirus?

Dr Vincent Rajkumar: I have been following India very closely. My parents are living in India, I have a lot of friends and family there. It’s a country that I’m hugely concerned about and from what I’ve seen there are many optimistic signs.

One is that there must be some level of cross-reactive immunity in India that is protecting the population because in terms of deaths per million, India has about 50 deaths per million and that’s ten times lower than the United States. So, to the extent that you have zero positivity in Mumbai, Pune and Delhi; you are not seeing the overflowing ICUs, and the huge number of deaths that we saw in New York or Lombardy. So something is protecting India which I’m very grateful for.

I think the government has done a really good job of trying to impose restrictions, trying to emphasise the need for masks. As long as the public is aware of taking just simple precautions – wear a mask, don’t join people in crowds, be very careful indoors particularly and keeping hands clean, as that alone will reduce the viral dose, if not prevent from getting an infection.

Also Read: Coronavirus Explained: What Are The Phases In The Clinical Trials Of The COVID-19 Vaccine?

NDTV: WHO has been emphasising about testing, tracking, to fight COVID-19. But in US recently, Centre For Disease Control (CDC) said that it’s not necessary for everyone to get tested, specially if you’re asymptomatic. What is your take on this?

Dr Vincent Rajkumar: I disagree with that statement by CDC. I think it’s clearly important to test asymptomatic people who have been exposed because they could act as a carrier. They themselves might be asymptomatic but the risk is that they could spread it to others just as efficiently, and cause very severe symptomatic diseases. It’s very easy to identify who these people are if they’ve been exposed to someone and take the necessary precautionary measures. I think we have to operate on the precautionary principle that asymptomatic people are there and if you can identify them, you should identify them and protect other people from getting infected.

NDTV – Dettol Banega Swasth India campaign is an extension of the five-year-old Banega Swachh India initiative helmed by Campaign Ambassador Amitabh Bachchan. It aims to spread awareness about critical health issues facing the country. In wake of the current COVID-19 pandemic, the need for WASH (WaterSanitation and Hygiene) is reaffirmed as handwashing is one of the ways to prevent Coronavirus infection and other diseases. The campaign highlights the importance of nutrition and healthcare for women and children to prevent maternal and child mortality, fight malnutrition, stunting, wasting, anaemia and disease prevention through vaccines. Importance of programmes like Public Distribution System (PDS), Mid-day Meal Scheme, POSHAN Abhiyan and the role of Aganwadis and ASHA workers are also covered. Only a Swachh or clean India where toilets are used and open defecation free (ODF) status achieved as part of the Swachh Bharat Abhiyan launched by Prime Minister Narendra Modi in 2014, can eradicate diseases like diahorrea and become a Swasth or healthy India. The campaign will continue to cover issues like air pollutionwaste managementplastic banmanual scavenging and sanitation workers and menstrual hygiene

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