Covid-19: What you need to know today

On Monday, former US Food and Drug Administration (FDA) chief Scott Gottlieb said in an interview to CNBC that his estimate is that by the end of the year 30% of Americans would have been infected by the Sars-CoV-2 virus which causes the coronavirus disease. That’s almost one in three Americans who will have some sort of immunity against the virus. I know there is a lot of confusing research on this, especially when it comes to those asymptomatic patients who have low viral loads, but I am going to go with the most comprehensive research – Dispatch 207 on November 19 covered it – that most infected people have at least six months of protection (of some sort) against Covid-19, with a not insignificant probability that this protection could actually last for years. Gottlieb went on to add in the interview that he believes some states may have an infection rate of up to 50%.

INFECTION ESTIMATE

Former US FDA chief Scott Gottlieb said in an interview to CNBC that his estimate is that by the end of the year, 30% of Americans would have been infected by the Sars-CoV-2 virus.

This bodes well for 2021, he suggested – and it’s easy to see why. If a third of the population is protected against the virus, there is a high chance of the chain of infection being broken before too many people are infected. “You are getting to levels where this virus is not going to circulate as readily,” he told CNBC. The US ended November with 13.6 million recorded cases of Covid. It could end the year with anything between 17 million and 18 million, at the current rate of growth of recorded cases. If Gottlieb’s assessment is accurate, this number, in reality, should be 100 million – which means that for every infection recorded, the US is missing around six. That seems plausible, and also highly probable. For the purposes of this column, I have assumed it to be true.

WHAT NEXT?

If a third of the population is protected against the virus in the US, there is a high chance of the chain of infection being broken before too many people are infected.

India has seen almost 9.5 million cases of the coronavirus disease to date (it is second in terms of the number of cases after the US). A direct extrapolation of Gottlieb’s constant (if it can be called that) might not make sense for a variety of reasons. India and the US are both large and have high population counts, but the differences between them on these two parameters are still stark. The US has a population of 330 million; India, 1.3 billion (1,300 million). The US has a land area of 9.8 million square km; India, 3.3 million square km. The US’s population density, based on these numbers, comes to 34 per square km; India’s almost 394 people per square km. Some of these factors point to the constant being higher in India; others, lower.

There are also other factors at play – populations in some parts of India, like populations in parts of Africa, may have some protection against the coronavirus disease on account of previous infections by other coronaviruses; and the BCG vaccine, which almost all Indian children have received for decades now, may offer some cover against the infection or, at the least, the intensity of infection.

In Dispatch 158, on September 15, I had put forth assumptions that around 15% of the urban population in India and 5% to 7.5% of the rural population may have been infected by the virus. That number was based on antibody prevalence surveys carried out in many parts of the country. Those numbers are sure to have moved north. It is likely that the metropolitan cities, such as Delhi and Mumbai, have infection rates of around 20%; other Indian cities, 15%; and rural India 7.5%. India’s top 10 cities have a population of around 110 million. At a 20% infection rate, they would have seen 22 million cases. India has a rural population of around 850 million people, and an infection rate of 7.5% translates into around 64 million cases. The remaining 340 million urban population would have seen 51 million infections at a 15% infection rate. That works out to a total of 137 million cases – which means that for every infection recorded, India is missing 15, which too is plausible. At an aggregate level, this translates into an overall infection (or exposure) rate of approximately 10%, although the number is likely to be far higher in some large cities, and much lower in some remote rural areas.

Interestingly – and I did not assume numbers with this end in mind, although it may now seem like that – at 137,000 dead (the current death toll in India), and 137 million infections, India’s infection fatality rate works out to 0.1%, which some experts believe to be a reasonable estimate of the Covid-19’s fatality rate. Sure, it is likely (very likely) that India’s actual death toll is higher, but it is just as likely that the number of cases is as well.