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Uncertainty over long-term immune response has implications for vaccine efficacy: Experts

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 the 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 the 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 said 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 re-infection 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 surveillance 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.