Covid-19 waning in hot weather, still a conjecture

He insisted herd protection may develop over time. If we try to rush it through, we will initially have a surge of cases which will overwhelm the health system and result in many avoidable deaths.

Q: When do you think coronavirus cases will begin to decline, after two weeks May will begin; and under extremely high temperature and dry conditions, how do you think this virus will respond?

A: The novel Corona virus causing Covid 19 is a new virus whose seasonality and response to hot humid weather is not yet fully understood. Some evidence suggests that it will wane in hot weather, like other corona viruses but that is still a conjecture. This view is still being debated.

Q: Some experts say we need to build herd immunity, would not this put our health system under extreme pressure, and also have a cascading effect on patients visiting hospitals with other ailments?

A: Herd immunity, better called herd protection, may develop over time. If we try to rush it through, we will initially have a surge of cases which will overwhelm the health system and result in many avoidable deaths. Even if you want to fill the sports stadium for the big game, you still have to regulate the flow at the entry gates to prevent a stampede.

Q: There is a huge demand for testing, would this help in containing the highly contagious viral infection?

A: Testing at higher rates would certainly help to identify infected persons better. However, high rates of transmission have been reported even in the pre-symptomatic period. That makes testing decisions difficult, as it would be logistically impossible to test all asymptomatic persons in the population. So, we have to use contact history and symptoms as the testing criteria to begin with. Syndromic diagnosis, which is symptom based diagnosis of influenza like illness, also helps to isolate persons at home even if testing is not widely available due to logistic constraints.

Q: Relapse of Covid-19, do you think is another big challenge, in the absence of a vaccine?

A: We do not yet know whether these are reinfections, reactivations or false positive tests in the first instance. We also presently know how long the acquired immunity lasts. If true reinfections occur, we have to manage them as we do fresh infections. Since the rate of ‘true reinfection' is unknown, we cannot presently estimate how serious a threat it would be.

Q: Is there a straight jacket approach to counter this deadly viral infection, if not, then what is the solution to combat Covid-19?

A: While public health principles are broadly common, specific strategies have to be customised to the country or state's population characteristics (such as urban-rural population ratio and age structure), health system capacity, availability of testing kits and competent labs and adequate supply of personal protection equipment and intensive care capacity in hospitals. Social distancing and personal hygiene practices are universal, while lockdown policies have varied between and within countries.

Q: District administrations across the country are closely monitoring hotspots and clusters and conducting random surveys on large populations under these areas, will this strategy yield concrete results?

A: This is the ideal strategy in a large country like India. We need coordinated policy making at the central level, multi-sectoral planning and coordination at state level and decentralised implementation, with scope for context specific innovation and adaptability, at the district level. Community engagements and multi-agency partnerships are also best energised at the district level.

Q: What is a gold standard test for Covid-19, which is capable of highly accurate results and completely removing false negatives?

A: RT-PCR with collection from the throat through swabs is currently the most advocated method. While it has been found to have very high sensitivity in hospital testing conditions, the sensitivity may vary in field conditions depending how well the sample is collected. Bronchial lavage will give an even greater assurance of adequate virus samples but that is not possible under field conditions and takes effort and time even in hospital settings.

Q: False positive result in asymptomatic persons, do you consider this a huge challenge?

A: False positive results become more frequent in persons who have a low prior probability of infection, especially at high levels of test sensitivity. An asymptomatic person, who has no travel history to an affected country or a domestic hotspot location in the country or has no contact history with an infected person, has a higher probability of testing false positive. However, this is presently considered as an acceptable risk by the public health agencies as isolation of a person who ‘might be infected' is considered necessary to break the chain of transmission. Even then, indiscriminate testing in the population should be avoided and clear criteria must be established for suspect case or exposed person testing and for random sample surveys in the population.