Covid-19 and Seroprevalence

Ritika Das (ritikadas108@gmail.com)

India has been experiencing a major catastrophic second wave of the Covid-19 since the end of March 2021 and as observed in all previous pandemics, this time to the second wave has been the deadliest and has already harmed lakhs of lives to such an extent that people are already worried and preparing themselves for the much-feared third wave.

But there are several recent studies and breakthroughs about the trend of this virus that claims to nullify the fact that a third wave will occur, and even if it does, it won't be as damaging as the previous ones.

One such breakthrough is the study of Seroprevalence. For simple understanding, it denotes the number of persons in a population who have tested positive for a specific disease based on serology specimens. To be more precise, serology specimen means to collect a sample of blood serum to detect antibodies that appear specifically in association with certain diseases.

It is often calculated as the percentage of the total specimens tested positive in terms of one lakh people being tested. The antibody in this disease usually gets detectable in the blood by 1-3 weeks after someone is infected. But this percentage will not be significant if the specificity of the antibody is low. Also, there are instances where it takes a longer time for the antibodies to form or even in some cases, antibodies don't form at all.

Along with the percentage of antibodies in people, the study of Seroprevalence also gave scientists and researchers a clearer perspective regarding the various dimensions of the Covid-19 virus and had provided them with equitable information and knowledge which in turn provided a base for better treatment of the infected patients.

For instance, when this survey was conducted in Wuhan, China which was the epicentre of Covid-19, it was revealed that there is a higher prevalence of Covid antibodies in the elderly population as compared to other age groups. It was also observed that asymptomatic patients had a greater risk of viral transmission compared to symptomatic patients due to delayed diagnosis and treatment.

The first nationwide SARS-COV2 serosurvey in India was conducted in May-June 2020 which had a low seroprevalence of 0.73%. The next nationwide serosurvey was conducted in December 2020-January 2021 which presented that one out of five Indians may have been exposed to the novel coronavirus until then, which meant that 21.5% of people were seropositive in the country. It was the highest in urban slums at 31.7%, dipped to 26.2% in urban non-slum areas and was the lowest in rural areas at 19.1%.

Also, as per the ATE Chandra Foundation model, the recent Seroprevalence in Mumbai should have reached a minimum of 40% of the entire population residing in the city which means that 40% of the entire Mumbai already has the antibodies due to vaccinations or previous infections. The positive thing about this finding is that when the UK experienced its Seroprevalence touching 60-65% in its population, there were reports of the sharp decline of new cases, and if we compare Mumbai's seroprevalence figures with it, then it can be taken as one of the notable reasons why at present Mumbai is experiencing a decreasing number of Covid cases. Many of the other cities in India like Delhi are also currently experiencing a similar flattening graph of Covid as the level of seroprevalence is increasing.

But according to the latest serosurvey done by ICMR, it is revealed that while Madhya Pradesh reported the highest seroprevalence (79%), the lowest seroprevalence was reported in Kerala (44.4%), followed by Assam (50.3%). This provides logical evidence to the current situation in Kerala which is contributing almost 70% to the total Covid cases in India while Assam remains one of the few states in India which is yet to recover from the second wave.

The current increase of the Seroprevalence level in some mega metropolitan cities in India is very important to the entire nation because, to begin with, the high Seroprevalence level contributes to boosting herd immunity against the virus which subsequently means that there will be less percentage of people getting infected in the future waves. In addition, this would also be a breather and relief for other smaller cities because as seen in the previous two Covid waves, it is the metropolitan cities that first gets infected and later spreads to smaller cities and ultimately to rural areas.

The serosurveys also lead us to the situation of Endemicity that India may experience in the future. Endemicity is a situation when a population learns to survive with the existing disease and the spread is limited with a predictable rate of growth. The serosurveys from other countries also help us to understand that while it could be possible that children may get infected in the third wave, it is very unlikely that they will have major complications or experience a high number of fatalities.

To conclude, this high Seroprevalence along with extensive vaccination drives by the government can boost the antibody level among the people to such an extent that the probable third wave which is assumed to cause more harm to the younger population, that is the children, can be avoided and prevented. But along with all these, people also have to adhere to the precautions and preventions listed by the WHO as well the government and continue properly wearing the masks and keep maintaining social distance in public places and do their bit to end this deadly cycle of the virus.