Express News Service

The recent release of the findings from a seroprevalence study by government agencies in Delhi which showed that nearly 23.5 per cent population may have antibodies against COVID-19 virus has triggered a lot of debate on how close the city could be to herd immunity. But there is also confusion around the protection against the disease as a recent research from the UK showed that antibodies against SARS CoV 2 may not be long-lasting. Dr Ganguly deciphers for our readers what these studies mean?

So far, what can be said definitively about immunological response towards the COVID-19 virus and what are the areas around which understanding is still to emerge?

I would say three major immunological insights that we could gather are-one, infected persons do mount a robust immune response against the virus, rather at times it’s too aggravated a response which is driving the disease to untoward ends. Two, all infected individuals are mounting both antibodies and T cell mediated immunity both of which play roles to protect the individuals from reinfection at least for some time. Thirdly, it seems the antibodies -at least the ones we have means to check- are rather short-lived, around 2-3 months. But as in the past 7-8 months no confirmed reinfection case has been reported from anywhere in the world, scientists believe either the T cells or antibodies which are longer-staying but not yet detectable by available assays are providing the protection for at least 7-8 months.        

A highly talked about study from the UK recently suggested that antibodies against SARS CoV 2 may not be long lasting and this led to a whole lot of speculation about long term immunity towards the pathogen. Can you please elaborate on what does this mean and what could be its implications?

As I said earlier, it means the antibodies we are looking for or which we have means to detect- are not very long-lasting. But absence of antibodies simply means absence of just antibodies, not absence of protection. Protection against a pathogen can be mediated by antibodies or T cells or both. Duration of immune protection can only be reliably noted from reports of reinfection, and till today there are none. Presence of antibodies is an easily detectable parameter to confirm infection in the recent past and thus very important for sero-surveillance efforts. Moreover, this perplexing realization of waning antibody levels in the absence of reinfections being reported brings forth the importance of T cell-mediated immunity against SARS-CoV2 which needs to be kept in mind while assessing all vaccine candidates. 

Just a few days ago, the Union government released the findings of a seroprevalence in Delhi which showed that around 23.5 % of the samples tested had antibodies against the virus. What does it mean in the context of the population’s immunological response to the disease?

This data means different things to different interest groups. To me the most striking revelation is sheer speed the infection is spreading with. Contracting almost 20% of the population in hardly 4 months. It also marks the magnitude of asymptomatic infections. But these data are done on representative samples and may not provide the real picture, which can be both higher or lower based on the type of errors and biases the sampling might have had. 

What are your views on herd immunity against SARS CoV 2? At what level of exposure to the virus, can the population be naturally protected against the disease?

Herd immunity has been a phrase people scared of uttering in this pandemic, due to sheer numbers of fatal infections we are experiencing. But in my understanding the race between vaccination and herd immunity will be won by the latter. I say this just because the virus is extremely contagious, due to its transmission through droplets and aerosols, as the infected individuals are infective for a long time and more importantly a large number of infected individuals have no clue about their infection in the absence of symptoms. Now this herd immunity will only be achieved if the immune protection is really long lasting. We do not have that data. Neither do we have any assurance for this holy grail of long-lasting protection from any report on vaccine trials. Time is the only experimental device that can give you this answer.

Is there anything about the virus and immunological response against it that has shocked or surprised you?

To me the major revelation was rather less robust immunity in asymptomatic individuals with the infection. The viral load was found not to be much different from the symptomatic individuals. More severe disease has a rather more robust immune response. So, the disease seems not to be a direct function of the infectious agent here, as is usual with most infections. It is rather a function of how the immune system of a given individual is responding to the infection. Aggravated immune activities are leading to damage to the body’s own constituents in some individuals and they are the ones rushing to untoward ends.