Influenza pandemics may hold clue for Covid outbreak

NEWDELHI: Scientists at the Centre for Infectious Disease Research and Policy in the United States have offered some clues about how the ongoing Covid-19 pandemic may evolve based on the experience and trajectories of previous influenza pandemics, four of which occurred in the last century.

The analysis, which maps out three distinct trajectories the Covid-19 outbreak can take, focuses on the northern hemisphere and developed countries but cautions that the impact in the so-called global south or developing countries could be worse, given the high population density and inadequate health infrastructure.

The scientists posited two key takeaways from comparisons with the influenza pandemics. The first that the outbreak may stretch to 18-24 months as immunity slowly builds up in the population. “Given the transmissibility of SARS-CoV-2 [that causes Covid-19], 60% to 70% of the population may need to be immune to reach a critical threshold of herd immunity to halt the pandemic,” the report said.

The other takeaway summarized three possible trajectories. The first sees the first wave of Covid-19 in spring 2020, followed by smaller waves over the next year before finally diminishing in 2021. “Depending on the height of the wave peaks, this scenario could require periodic reinstitution and subsequent relaxation of mitigation measures over the next 1 to 2 years,” the study found.

The second scenario sees a second wave follow the first wave in the fall or winter of 2021 and smaller subsequent waves in 2021. “This pattern will require the reinstitution of mitigation measures in the fall.” This pattern is similar to the 1918-19 influenza pandemic. The third scenario showed the first wave of Covid-19 in spring 2020 followed by a “slow burn” of ongoing transmission and case occurrence but without a clear peak.

“Whichever scenario the pandemic follows, we must be prepared for at least another 18 to 24 months of significant Covid-19 activity…,” the scientists wrote.

The study cautioned that while the Covid-19 and influenza pandemics had similarities, there were important differences.

The two pathogens differed in the incubation period (2-14 days for Sars-CoV-2 and 1-4 days for influenza), the percentage of asymptomatic patients (higher for Sars-Cov-2), and significant pre-symptomatic transmission of Covid-19.