The third wave of COVID-19 in India– if it occurs — is unlikely to be as severe as the second wave given the extent of spread of coronavirus infections that has already taken place in the country. A latest study report, authored by Sandip Mandal, Balram Bhargava and Samiran Panda from the Indian Council of Medical Research, and Nimalan Arinaminpathy from the Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK, was based on a mathematical modelling analysis and published in the Indian Journal of Medical Research.
In order to show the plausibility of a third wave of COVID-19 in India, the researchers used a deterministic, compartmental model of SARS-CoV-2 transmission, four potential mechanisms — waning immunity restores previously exposed individuals to a susceptible state, emergence of a new viral variant that is capable of escaping immunity to previously circulating strains, emergence of a new viral variant that is more transmissible than the previously circulating strains and release of current lockdowns affording fresh opportunities for transmission — for a third wave were examined.
The study said that infection-induced immunity may reduce over time, causing re-infection of those previously exposed, even if the circulating virus remains unchanged.
Considering the hypothesis of an emergence of a full immune escape variant, the study said even if immunity remains lifelong, it is possible for a new variant to emerge that is capable of escaping the immunity induced by the previously circulating strains.
The study findings highlighted that immune-mediated mechanisms (waning immunity, or viral evolution for immune escape) are unlikely to drive a severe third wave if acting on their own, unless such mechanisms lead to a complete loss of protection among those previously exposed.
Also plausible mechanisms for a third wave include a new variant that is more transmissible and at the same time capable of escaping prior immunity, and lockdowns that are highly effective in limiting transmission and subsequently released.
“In both cases, any third wave seems unlikely to be as severe as the second wave. Rapid scale-up of vaccination efforts could play an important role in mitigating these and future waves of the disease,” the study stated.
“This study demonstrates plausible mechanisms by which a substantial third wave could occur, while also illustrating that it is unlikely for any such resurgence to be as large as the second wave. Model projections are, however, subject to several uncertainties, and it remains important to scale up vaccination coverage to mitigate against any eventuality. Preparedness planning for any potential future wave will benefit by drawing upon the projected numbers based on the present modelling exercise.”