Many countries saw a drop in cases. There are lessons – analysis
A close look at the trajectory of Covid-19 in Europe reveals that the number of deaths in the four critical countries (Spain, Italy, Germany, France) has suddenly decreased and has been reduced to double digits daily.
Even the United Kingdom and the United States (USA), with their sudden and abrupt initial spike in infection and death rates, appear to be on the road to recovery. Are there specific lessons on this? Have these nations already reached a peak and is infection now on the decline? Is the increase in recovery rates related to this and, more importantly, does this mean a downward trend in virulence?
The current pandemic is unique not only because it is caused by a new virus that puts everyone at risk, but also by the dichotomy of host immunity. It is a unique case of innate immunity (pre-existing, transmitted by the mother from birth) in overdrive mode leading to a cytokine storm in more severe cases.
Adaptive immunity is suppressed, which is more powerful, long-lasting and desired. The challenge is to develop therapeutic strategies to maintain an optimal balance between the two, to stop viral replication and promote the destruction of virus-infected cells.
Infection rates and clinical severity of Covid-19 patients are highly variable between populations. As of June 16, more than 8.15 million cases and more than 439,000 deaths have been reported from 216 countries / areas or territories. India reported a test positivity rate of 5.8% of a total of almost 59 lakh tests and only 7.0 deaths per million population.
For such a densely populated country, and despite the recent increase due to openness, these figures are remarkably low compared to critical points in Europe and the US. USA, where up to 15% of cases and significantly higher deaths have been reported. is that there are relatively few serious / critical cases in India and the mortality rate of all positive cases is very limited (less than 3%).
The population-specific heterogeneity observed in infection rates and clinically different patterns (morbidity and mortality) are due to two factors, namely, virus virulence and host susceptibility, which are interdependent and together result in manifestation of infection.
A virus that is virulent in one environment may be harmless in another. On the other hand, the susceptibility of the host depends on the genetic diversity of the genes that control the immune response in a population. The latter is made up of various microbial and geographic pressures, which are a hallmark of evolutionary selection and immunity to new pathogens.
Once the peak is reached, the virus can continue to replicate, albeit at lower levels compared to immune recovery, as reflected in the percentage of recoveries.
It is noteworthy that nations with a recovery rate of 70% and more (China 94.3%, South Korea 90%, Germany 91.3%, Scandinavian countries 82-95%, Italy 71%) have been able to reverse the trend with a reduction significant Number of new cases and daily deaths. So-called latent infections can lead to more asymptomatic cases that can improve immunity. Government responses must continue to focus on detecting and isolating people infected with symptoms.
More good news comes from New Zealand, which became the first country with zero active cases, while neighboring Australia, with a recovery of more than 92%, also resumed normal activities.
The recovery rate in India has been almost static at 48% since June 1 due to increased public activity, leading to a daily increase in the number of new cases. This is displacing recovery later in weeks, perhaps months. The focus should be on slowing the spread of the virus. To accomplish this, novel strategies must be developed that can vary from state to state. The goal should be to achieve recoveries above 70% as soon as possible.
India’s situation is not much different from that of Russia and Brazil, as both reached high numbers and still report significantly high infection rates on a daily basis.
The big question everyone is asking is whether we expect the spike in India along with the subsequent decline in infection rates in the short term. It is conceivable that in such a vast country, a single peak cannot be expected and the long-awaited decline in numbers will differ in different regions.
Today, it is clear that many more people will become infected and self-help groups must move forward to make Covid-19 a people movement. The three golden principles of wearing masks, social distancing, and hand hygiene are the only ways to contain the pandemic.
A recent study published in the UK (BMC Medicine 2020) concludes that physical distancing measures substantially reduce contact levels to approximately 74% and this can help considerably mitigate the spread of the virus, which could lead to a decrease in cases in the coming weeks. The real challenge for us would be to focus on keeping mortality rates low.
Understanding the host’s susceptibility to the SARS-CoV-2 virus is a key step in identifying a vaccine. It will also help determine why the disease is mild for some people but life threatening for others. Science must also examine whether recovering patients can develop lasting immunity against reinfection and whether reinfected ones will develop a milder form of the disease compared to those who were not previously infected.
Dr. Narinder Kumar Mehra is Emeritus Scientist of the Indian Council of Medical Research
and former dean of the All India Institute of Medical Sciences, New Delhi
The opinions expressed are personal.