‘20%-45% infected in 2nd wave’ in Mumbai: Study
THE MODEL TAKES INTO ACCOUNT THAT THE SECOND WAVE IN MUMBAI BEGAN ON FEBRUARY 15
MUMBAI: The second wave of Covid-19 pandemic has so far affected 20%-45% of Mumbai’s population, according to an estimate by a mathematician from Middlesex University, London.
A significant part of these infections could be reinfections, suggested the model by Murad Banaji, senior lecturer in mathematics, department of design engineering and maths at the university, who has been studying the epidemic in Mumbai. Banaji has used Monte Carlo simulation – a mathematical technique used to estimate possible outcomes of an uncertain event in multiple scenarios.
The model by Banaji takes into account that the second wave in Mumbai began on February 15. Between February 15 and May 21, around 380,000 new cases were added to the city’s tally.
“A broad estimate is that between 20%-45% of the city’s population have so far been infected during the current wave. The estimates assume that there will be around 4,000 recorded deaths associated with infections acquired during this surge so far,” said Banaji.
“Cases have not increased much in the last week. Daily fatalities have come down, so second wave recorded fatalities could end up at less than 4,000 – we’ll have to wait and see. But the broad conclusions should still hold,” he added.
The surge in infections in the slums suggests that a significant percentage of infections in the slums during this wave could have been reinfections, Banaji said. “It would be great to have more clarity - hopefully the Brihanmumbai Municipal Corporation will eventually share data on cases where the same individuals tested positive more than once. Of course, because of very limited testing in the slums during the first wave, case-data may not shed much light on reinfections. But it would likely still prove valuable,” he added.
Sandeep Juneja, dean of the school of technology and computer science at the Tata Institute of Fundamental Research, Mumbai, who has also been running simulation models to understand the transmission of Covid-19, said, “Our own estimates are on the lower side. More of the order of 12-18% population got newly infected during the second wave. Although we need information on reinfections to be more certain.
Also, it may well be that the current strain leads to a larger proportion of population being symptomatic and hence a larger proportion getting tested and getting detected. This is plausible but we lack the research to confirm this. Given that most infections are in nonslums, one in any case expects a higher detection rate. A higher detection rate would imply a lower percentage of the population affected in the calculations by Banaji.”
While Banaji’s estimation suggests a significant number of reinfections, Juneja said it was difficult to project reinfection cases. “We need a different method to arrive at reinfection numbers. For example, seeing what percentage of the population tested positive this time while they had tested positive in the last wave as well,” said Juneja.
Rahul Pandit, a city-based pulmonologist and part of the state’s Covid-19 taskforce, said, “We are seeing some reinfections but not significant. Most cases are new ones. Mathematical models are based on various assumptions. So they may be accurate only when these assumptions are true.”
“We know that prior infection and partial vaccination are likely to reduce severe disease. After an earlier Covid infection or single dose vaccination, people may still get infected and even transmit the disease – but they are less likely to fall severely ill, be hospitalised, and die. When we look at cases during this wave, it is clear that there were a significant number of infections in the slums; but reports have not described a surge in hospitalisations from the slums. This could be because a large number of the infections were reinfections this would be consistent with serosurvey data which indicates high levels of infection in the slums by the end of 2020,” Banaji said.