Mumbai’s daily Covid-19 cases are climbing sharply. Over the past week, cases have averaged almost 1,600 per day – triple the number one month ago. Meanwhile, a small but increasing fraction of the city has had at least one dose of a Covid-19 vaccine, probably around 4% to date.
How bad is the city’s third Covid-19 surge? And where is it likely to go next? Could vaccination halt the wave?
These are difficult questions, but we now understand a lot more about Mumbai’s epidemic than one year ago. This added knowledge means that we can put the numbers into perspective.
How fast is disease spreading?
We know from serosurvey data that recorded cases represent only a fraction of total infections. These surveys involve sampling populations to estimate “seroprevalence”, that is, to find how many have antibodies to SARS-CoV-2, the virus responsible for Covid-19. This fraction of infections noted in the survey is likely to be much lower in slums than in nonslum areas. We…