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  • 08 June, 2021

  • 8 Min Read

Covid-19- DOTS framework to mitigate the 3rd wave

Covid-19- DOTS framework to mitigate the 3rd wave

‘R’ and determinants

  • The reproduction number — often referred as R — is the average number of new infections arising from one infected individual.
  • R fluctuates over time during an epidemic.
  • When R is greater than 1, infected individuals infect more than one person on average and we observe increasing cases.
  • When it is less than 1, cases are declining.
    • It is not a perfect statistic, especially when cases are low, but it does provide helpful insights into how an epidemic is changing.

What led R to increase earlier this year resulting in a second wave?

  • R depends on four factors, summarised by the acronym DOTS:
    • Duration a person is infectious;
    • Opportunities infected individuals have to spread infection to others;
    • The probability Transmission occurs given an opportunity, and
    • The average Susceptibility of a population or subpopulation.
  • Because each factor is required for increasing cases, reducing any of them to 0 would extinguish an epidemic.
  • This is not practical right now anywhere in the world.
  • However, we should work toward decreasing these factors such that R remains as low as possible.

Susceptibility, opportunities

  • Let us start with S — the proportion of the population susceptible to infection.
  • Susceptible individuals lack immunity derived through prior infection or immunisation.
  • Results from a national seroprevalence survey done in December 2020 and January 2021 indicate that roughly 25% of the population had antibodies to the virus that causes COVID-19.
  • Estimates were slightly different depending on geography.
  • And some surveys showed substantially higher exposure to the virus.
  • Nevertheless, there was still a substantial susceptible population in most parts of the country at the beginning of 2021.
  • Susceptibility can be reduced through immunisation.
  • By the end-March, however, less than 1% of the total population had received two doses of the vaccine.
  • Taken together, the right conditions were set for a potential second wave at the beginning of 2021.

Opportunities for transmission

  • The next factor is the number of opportunities for transmission — or O in the DOTS.
  • Many people were eager to get back to life and work, especially after a very challenging 2020.
  • Social distancing had reduced and markets filled again with people.
  • One salient characteristic of COVID-19 is that the disease is driven largely by superspreading, where many individuals are infected by a small number of individuals.
  • Increased social mixing and large gatherings that took place in early 2021 also might have helped facilitate a second wave.

Transmission, duration

  • This brings us to T, or the probability of transmission.
  • Not taking proper precautions can lead to increased transmission.
  • One new variant called B.1.617.2, or more recently known as the delta variant, is known to be much more transmissible — potentially twice as much— than those circulating in 2020.
  • This is demonstrated by the fact that it is the dominant variant in India and has emerged as the dominant variant in the United Kingdom according to data from there.

Duration of infection

  • Finally, the last factor in the DOTS equation is the duration of infectiousness or D.
  • Emerging evidence suggests that the duration of infectiousness could be slightly longer with some new variants.
  • More research is needed to confirm this.

A third wave?

  • First, we need well-designed seroprevalence surveys to understand how much of the population remains susceptible and where they reside.
  • The Government has planned a seroprevalence study in June in the same 70 districts where the first three rounds were conducted.
  • There also remain questions about waning immunity and the potential for reinfections, which would affect how we calculate the proportion of the population that is susceptible.
  • The new variants also complicate this equation, as they are able to partially evade immunity developed through infection or immunisation.
  • Despite the need for more data, based on the existing evidence and out of an abundance of caution, we should anticipate that there could be a potential third wave.

Importance of DOTS framework

  • Luckily, DOTS provides us with a framework for preventing or mitigating a third wave.
  • We need to drive down the factors that contribute to R wherever possible.
  • And we need to work even harder to do this, because the new variants have skewed the equation such that R can more easily be pushed to be greater than 1.
  • Some regions have implemented lockdowns, which substantially reduce opportunities for transmission.
  • These are temporary solutions and should be used to focus on slowing transmission and scaling up other interventions.
  • Mass gatherings have also largely stopped, which should help reduce opportunities for transmission.
  • Currently only 3% of the population has received both doses.
  • The Government is working hard to procure additional doses that are desperately needed.

Mask use, ventilation

  • Transmission can be reduced through increased use of face masks and improved ventilation.
  • Research from neighbouring Bangladesh indicates that providing free masks together with community monitors can help improve adoption.
  • Last, if the duration of infectiousness is indeed longer, isolation and quarantining guidelines should be revisited to minimise potential exposure to others.

Conclusion

  • The emergence of new variants means we need to take these interventions even more seriously.
  • Connecting the DOTS, though, can help mitigate a third wave and the tremendous pain and suffering that have become all too common in recent weeks.

Source: TH

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