Uncertainty over long-term immune response has implications for efficacy of COVID-19 vaccine, say experts

New Delhi: The rapid spread of COVID-19 in communities across the globe and the resurgence (second wave) suggest the possible role of asymptomatic persons in its transmission, while the uncertainty over long-term immune response has potential implications for the efficacy of vaccines, experts have said.The role of reduced use of non-pharmaceutical interventions in facilitating a second wave of COVID-19 as community engagement wanes requires further investigation, they said.If strong supportive evidence becomes available about the possible role of asymptomatic persons in the transmission of coronavirus infection, continued use of masks and the use of other public health measures may be advocated, according to an editorial in the ICMR's Indian Journal of Medical Research.The editorial titled 'The enigmatic COVID-19 pandemic' has been penned by Rajesh Bhatia, former director of Communicable Diseases for WHO's South-East Asia Regional Office, and Priya Abraham, director of ICMR-National Institute of Virology.

It mentioned that during the early phase of the pandemic, COVID-19 was presumed to be a non-relapsing disease. "New studies suggest the possibility of repeated virologically confirmed infections. Confirmation of reactivation or reinfection and their epidemiological importance are awaited," it said.

Serosurveillance is generally a sensitive tool to determine the extent of infection and immunity in the general population. Only a few field-based studies have generated serosurveillance data but with inconclusive inferences.The editorial mentioned a recent seroprevalence study which showed that most of the population of Geneva, Switzerland, remained uninfected during this wave of the pandemic, despite the high prevalence of COVID-19 in the region."Such studies raise red flags on continuous susceptibility of the population to COVID-19 and inability of the virus to produce widespread immunity. It may contribute to a second wave' of cases."The role of reduced use of non-pharmaceutical interventions in facilitating a second wave as community engagement wanes, requires further investigation," the experts said.The uncertainty of long-term immune response has potential implications for the efficacy of vaccines. The real impact of vaccines on this pandemic will become evident only once it has been widely in use for a few months in different populations, they said.As of now, vaccine is being considered as the ultimate intervention to contain the pandemic. The global race to make it available to the world has been accelerated.Currently, there are about 165 different candidate vaccines for COVID-19 being developed around the world and several of these are in different phases of clinical trials.Three vaccine candidates (inactivated, DNA based recombinant and ChAdOx1 nCoV-19 vaccine consisting of the replication-deficient simian adenovirus vector ChAdOx) are currently in early phases of human trials in India, the editorial said."Commercial production of COVID-19 vaccine and possible imports are likely to commence by the end of 2020," it said.Global procurement and distribution of vaccine to ensure its universal access has been planned by the WHO, Global Alliance for Vaccines and Immunizations (GAVI) and Coalition for Epidemic Preparedness Innovations.India has developed a blueprint for efficient deployment of the vaccine, supported by IT-based vaccine tracker."Immunizing the entire population, prioritising high risk segments, assuring quality in logistics and undertaking post-vaccination surveillance for adverse effects and impact on disease burden shall be huge challenges for any health system," it highlighted.In the absence of specific antiviral drugs or vaccines, non-pharmaceutical interventions undertaken by the communities assumed critical importance in curtailing viral transmission. "Community engagement, especially of poor and illiterate, is always difficult to ensure", it said.The COVID-19 pandemic has attracted the entire focus and efforts of the health system. Usual health services to communities have become restricted because health facilities are overwhelmed with COVID-19 patients, it said.People are also apprehensive about visiting health institutions for fear of contracting COVID-19. Important components of health services that have suffered most include health needs of children, women, elderly with noncommunicable diseases and management of other therapies (eg, cancers, tuberculosis and HIV) and health emergencies.The pandemic has pushed back progress made under the Millennium Development Goals and is hampering achievement of ambitious UN Sustainable Development Goals."It is still not clear as to how the global community will make up for the pandemic-induced setback to its critical operations of major disease elimination programmes such as for tuberculosis," the editorial said.Implementation of efficient public health actions is possible on the foundations of sound scientific knowledge of the characteristics of SARS-CoV-2."Despite extensive research on all aspects of COVID-19 pandemic, the world is still struggling with the origin of the virus, public health implications of the mutations in the viral genome, availability of a diagnostic test with better sensitivity and specificity, understanding the immune response to the virus, its pathobiology and clinical spectrum, and availability of safe and efficacious specific antiviral drugs and a vaccine."These unknowns have made it an enigmatic pandemic till now," the editorial said.