Corona Daily 311: Who Infects Who

 

India is generally associated with numbers that boggle the mind. It has 900 million voters, adds 13-14 million people every year, in ten years it will become the first country with 1.5 billion people. Not surprisingly, the largest contact tracing study ever was conducted in India. Its results were published yesterday. Researchers from American universities worked with the public health officials in two southern Indian states. Andhra Pradesh and Tamil Nadu together have 128 million people, and are among the most affected, or infected, Indian states. The researchers analyzed nearly 85,000 cases and 600,000 of their contacts to understand who infects who.

The study has at least five important takeaways.

*****

First, the ability of a few to spread the infection widely. The study found that 5% were responsible for 80% of the infections, while 71% didn’t pass the virus to anyone else. The Pareto principle (80/20 rule, e.g. we wear 20% of our clothes 80% of the time, and 80% only 20% of the time) seems to apply to the virus-spreading. Immunity or the lack of it may explain the ability of the person to “take in” the virus. For reasons not known yet, some people have a superior ability to “give away” the virus. If we were to find a way to recognize such super-donors, it may become possible to isolate them to curb a surge.

*****

Second, deaths in these two states increased with age, as can be expected, but dropped off after 65. This is good news for the 70+ and 80+. The possible reason is India’s life expectancy which is 69. (USA is 79). Remember 69 is the average. Many poor people, or those with little access to health care, die by 65, with or without Covid-19. Those Indians who survive beyond 70 are relatively better-off, with access to India’s best doctors and hospitals. That may explain why many elderly Indians are surviving infections. In the two researched states, until 1 August, only 18% of the deaths were among individuals older than 75. (In the USA, 58% of the dead were older than 75).

*****

Third, among those who died, the time between hospitalization and death was only 5-6 days. (USA 14 days). It suggests patients are brought to the hospitals too late, or due to being overwhelmed, hospitals admit only the most serious cases.

Among the dead, 62% had at least one co-morbid condition (USA 22%). Nearly half of Indian patients had diabetes, and one third had hypertension.

The Death rate was higher among men, a well-known fact. Men accounted for 62% and women 38% of the deaths.

*****

Fourth, index cases, the initial infectors were mainly men. They passed it on to others younger. It is possible Indian men move around more than women. Also, when the contact tracers call over the phone, it is likely the men talk to them more often than the women.

The elderly passed on the virus to people their own age. Not surprising that people similar in age mix with one another.

*****

Fifth, children of all ages can get infected and can spread. More than 5300 children in the study had infected 2500 contacts. Again, just like the elderly, children spread the virus to other children of a similar age. Possibly important information for the education minister before reopening schools.

*****

The research reported that India’s strict countrywide lockdown benefitted in reducing transmission. Tamil Nadu and Andhra Pradesh have better public health. The study must be considered as the best case scenario, before translating the results to another Indian state.

Ravi