COVID-19 1.0: Testing, Maharastra Morbidity and Herd Immunity
By Sandhya Mishra
In an interview with Sandhya Mishra, prominent epidemiologist Dr. Jayaprakash Muliyil offers a reality check for the COVIID-19 situation in India as well as plausible solutions for its riddance.
Are we under-testing for COVID-19?
The judicious way of testing the people is not something to pacify them. Testing is more of a technical issue. The way you can't ask a doctor how many X-rays he should take in that same way tests are technical matter that has to be done when it is required.
Testing for COVID19 allows us to see the magnitude of the problem and also to have a better diagnostic efficiency.
It is crucial to test for coronavirus to diagnose a person who is ill or has serious respiratory problems and is a straightforward thing to do. However, the problem is an early phase of the disease. When the person contracts the coronavirus infection, the incubation period starts and during the latter part of this period, the virus starts to appear in his/her system. Also at this stage, the person is not showing any symptoms and if you happen to test him, he will test positive for the disease. Soon he/she may or may not start exhibiting the symptoms and a week later, the virus will disappear from the system causing the test to be negative. So we have a problem here.
If you test every symptomatic person, he has already finished infecting quite a few people.
Or even if you do house to house testing, it could happen that you do pick up a few patients where he/she may be the last one to have got infected while others would have finished their infection cycle because in them there was no clinical disease but only a subclinical infection.
One could also test the family members of a person who have been diagnosed to have COVID 19 but problem with that testing is the positivity of the virus which the test reveals is transient, in other words, the test soon becomes negative.
And that is why containment becomes extremely difficult. We have an enemy which cannot be seen. Without testing it is not possible to contain the disease but, having said that in practical terms it is very difficult to carry out. One can be fairly certain patient will test positive for the virus during the first week of infection and subsequently another week after the infection but not after that.
Prominent epidemiologist Dr. Jayaprakash Muliyil
In a very recent study from California, a different way was devised to test the infection using the disease induced immunoglobulin IgG. The test becomes positive about 2 weeks after the infection and then it remains positive for a lifetime. The study also says that for every case there are 50-80 other hidden infection which do not come out because either the patient does not develop the symptoms or his symptoms are so mild that he/she could notice it.
The IgG test tells about how many are infected in the community and the spread of infection. Also, if you go by average, if you get infected, the chances are that you get a mild or subclinical infection and develop immunity for lifetime or in other words you are guarded from further infection for a lifetime; However, I do not have any evidence to prove this. One of the study in South Korea shows some of the people do carry the virus for few more weeks and how long we don't know.
How different States are Faring?
Kerala
Kerala has done very well in terms of containing the transmission. It is quite helped by the fact that there was a lock down. It is different from other states because government and people work together unlike anywhere else in the country.
On one hand, the curve has flattened in Kerala and they are hoping to get rid of the bug but on the other hand, the state is busy preparing adequate number of the bed and facilities so that when they open up after the lockdown. In case there is an onslaught they will be ready even for that and that is a logical approach to disease control.
Maharashtra and its High Mortality Rate
The case fatality is the difficult kind of a figure it depends on your numerator and denominator.
Numerator will be the number of patients who died of COVID-19— there is no way to classify the death as a COVID19 death other than testing his swab. What if the patient died at home? Do you know whether he died of COVID? If a state decides not to do anything about COVID-19, you will have zero deaths reported for the disease. So your case fatality due to coronavirus is calculated zero. Thus, reporting death in a right manner matters. Maharashtra, I think, is sincerely reporting the deaths.
Whereas, the denominator is the total number of people diagnosed positive of the disease. Now when you are only testing those people with a respiratory illness or pneumonia, you are likely to have a higher death rate. But suppose your cases include milder disease or patient with a contact history or family members who tested positive, your denominator increases.
But unfortunately this is not a correct approach. Now if you calculate infection mortality rate for COVID-19, it is much lower than the case fatality rate purely because lot of people get infected and very few people become cases or sick cases. So it all depends how do you arrive at denominator.
There are many other anomalies that may attribute to confusion or hinder the characterisation of the major patterns of the disease or deaths.
One must worry about where are the patients reporting disease or deaths. The areas where low cases and low deaths are reported should make you worry because probably there is no work is going on. If a death is reported to a hospital that has a good physician who can test and do the diagnosis or the one that has X-ray or CT-scan available or RT-PCR you can sort of fairly confirm the deaths that are due to COVID-19.
If a patient comes after some days of onset of disease, you may not pick up the virus but it will still be COVID-19 death.
Or a possibility that somebody got the fever and he tests positive but he is just a carrier of COVID-19, also exists.
Is Lockdown the Best Strategy to combat Novel Coronavirus?
When you think very carefully about it, containment and isolation has limited value in preventing the spread because those with subclinical infection can also spread disease. You cannot test the whole population of the country and even if you did the testing has to be repeated every other week and that will be a phenomenal exercise.
In India, there are nine and a half million deaths every year. Every month we expect 7.5L or 8L deaths. At the moment we have forgotten about everything and we are only focusing on deaths due to COVID-19. Due to lockdown, the classic accidental deaths have come down, but acute illnesses like myocardial infarction, meningitis, pneumonia, etc are being ignored. We have also stopped immunising our children, especially against whooping cough and diphtheria which could cause serious outbreak among them. So we can't afford to do this business of lockdown for a long time. Somewhere along the line we have to start living cautiously.
Are we in Community Transmission?
In many parts of India, especially in cities it appears that community transmission has indeed been established. Under such circumstances isolating the infected will have little impact on disease transmission. Each one of us have to make sure that we protect ourselves through maintaining safe distance and wearing mask. This can slow down the rate of disease transmission. Given the circumstances, we have another option to pursue.
What is Herd Immunity?
The viral epidemics travel from one person to another; after a certain point in time, the epidemic stops as we reach herd immunity. Here, the density of immune population increases which protects the susceptible population because now there is an invisible wall of immune people around the susceptible person. In H1N1 outbreak, 40% of the people were infected and that's when it stopped and we call that level of 40% as the herd immunity. Once you reach this level, you find almost overnight the disease disappearing. Each disease has its own herd immunity requirement. It is estimated that for COVID-19, it is 60% but it is an approximate figure.
The Way Out!
There is one other way but first let’s understand the mortality pattern. In young people it’s not very fatal and chances that a 25 year dying because of the disease is 30 out of 100,000; this particular level is less than a road traffic accident rate. The mortality in younger group in first or second decade of life is even lesser. The fourth decade is little high and for fifth is even higher. Above 60, it is quite high. For an 80 year old, probability of him dying is about 8400 out of 100,000, and if you put it in percentage it is 0.4%. But this also mean that there is more than 91% chance that he or she will not die. Towards our march to attend herd immunity, most of the deaths that would take place will be in the elderly; to be precise 80% of the deaths will be above 60 years of age.
One way we can do this safely, is by keeping the retired population away which is about 8.5 % of the population. Most young persons will face the infection without any problem while some will need hospitalisation and will recover. But if everybody is in the battle together to get the care then most of the beds would be occupied by the elderly, such that there will be no beds available for the young. Somehow or other we have to keep the elderly out of the battle. They must be requested to isolate themselves from infection.
There will be many challenges to implement this especially for the small huts or the slums in cities which is only the small portion of the Indian population. But majority should be able to adopt this measure for what we are asking them is nothing much but to keep the physical distance from others and look after them for maybe 5-6 months. Once we reach herd immunity they can all come out as there will not be any more active transmission of the virus.