Another point of view
First Lockdown in India - was it good strategy?
Most nations including advanced, affluent ones have not been able to control COVID19 transmission.
The pandemic continues unabated as long as the density of the susceptible population is greater than the threshold herd immunity density but when this critical point is approximately reached the epidemic begins to wane, and ultimately die out.
We may slow it down by measures like lockdown, universal mask use, hand hygiene etc but none of the strategy can terminate it.
What makes pandemic virus infect more and more people?
The major factors which promote the spread are low infective dose, R0 2-4 depending upon susceptible population and overcrowding particularly in poorly ventilated spaces.
The more and more use of protective gear by general population like universal masking, personal hygiene and social distancing are the ways to bring down R0.
The minimal infective dose is defined as the lowest number of viral particles that cause an infection in 50% of individuals
SARS-CoV-2 is a new pathogen we lack data on so far (for SARS, the infective dose in mouse models was only a few hundred viral particles). It appears that relatively low infective dose is needed in case of COVID19 because the virus is spreading relatively more efficiently.
On the basis of previous work on SARS and MERS coronaviruses, we know that exposure to higher doses are associated with a worse outcome. This may be likely the case in COVID-19 as well in the current pandemic as severe illness and mortality is reported much more in young HCWs (working in Covid wards) compared to young people in general population.
In the COVID-19 clinic and wards the purpose of donning PPE is to prevent such large exposures to HCWs to prevent high dose infection.
After exposure to sufficient inoculum dose
our ‘innate immune system’ detects virus infection and mounts an innate immune response which is not the virus-specific, unlike acquired immune (characterised by interferon, neutrophils and cytokines)
causing no symptoms or some symptoms : fever, headaches, muscle pain (asymptomatic and symptomatic cases) This response serves two purposes: to slow down the replication and spread of the virus, giving time to ‘acquired immune response to kick in, in the following week which will stop and finally clear the infection. Such response fortunately occurs in most infected individuals.
In older people and those with co-morbidity, the immune response not being robust the virus keeps replicating and spreading in the body, the inefficient innate immune response keeps increasing leading to uncontrolled inflammation due to ‘cytokine storm’ (serious/ critical cases).
Generally the highly symptomatic individuals cough up large quantities of virus and asymptomatic/pre-symptomatic individuals shed small quantities, this rule may be digressed by later group not uncommonly with several cases reported as super spreaders in these groups.
The lockdown may have been successful in staggering the rapidity of this process rather than terminating it. First lockdown in India achieved the same and gave us time to get prepared (masks, PPE, sanitizers, health infrastructure), it is another thing that we did utilise it though not fully. Universal mask wearing and hand hygiene is another way to achieve the same results. Both strategies aim towards the same, the first may work better with unaware, uneducated population albeit at enormous economic cost. The latter will work better with educated and aware population.
This pandemic will keep on occurring with large widespread outbreaks or repeated small scale outbreaks till threshold herd immunity is achieved by disease or the vaccine.
In hindsight, the huge inadvertent, ‘collateral gain’ from the first lockdown is that it has given us greater chance of survival than citizens of USA, UK, ITALY, SPAIN. If we compare the death rates, it is as high as 5-10% in these countries whereas in our country deaths are less than 3%. This despite the fact that these western nations have a far, far better and advanced healthcare delivery system than ours.
The pandemic peaked after several weeks (2-3 months) in our country. We learnt a lot from the experience of scientific community of these western countries during this time.
By then guidelines got standardised, with the role of steroids, tocilizumab and LMWH clearly well defined. Imagine the treatment plans in our country without this western data.
Will the vaccine come to our rescue?
There are following possibilities (and some due to fast tracking the development of vaccine)
1. Vaccine may arrive earliest in next 6-12 months by that time this RNA virus (like influenza virus) may get mutated resulting in a non-effective vaccine.
2. Vaccine may not work well in older age group and persons with co-morbidities like influenza vaccine. (The main purpose of vaccine stands defeated)
3. Vaccine works but precipitates PIMS TS / MIS-C. (Long term data shall avoid this eventuality but whole world is in a hurry to have the vaccine asap.)
4. Vaccine behaves like dengue vaccine
5. Effective vaccine arrives after threshold immunity in the community has been achieved.
6. Very effective vaccine is developed and universal vaccination is carried out to control disease transmission(a Herculean task)
Discovery of more effective treatment or vaccine is being eagerly awaited till then
‘Covid would be down intermittently but not out’
The debate shall go on!
Dr Shyam Kukreja
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