Many countries saw a dip in cases. There are lessons

Achieve a recovery rate of over 70%, follow social distancing, and understand host susceptibility to virus

Aclose look at the Covid-19 trajectory in Europe reveals that the number of fatalities in the four hotspot countries (Spain, Italy, Germany, France) has suddenly decreased and is down to double digits daily.

Even the United Kingdom and the United States (US), with their initial sudden and steep rise in infection rates and deaths, appear to be on the path to recovery. Are there specific lessons in this? Have these nations already reached a peak and is the infection now on the decline? Is the upsurge in recovery rates related to this and, more important, does this signify a downward trend in virulence?

The current pandemic is unique not just because it is caused by a new virus that puts everyone at risk, but also because of the dichotomy of the host immunity. It is a unique case of innate immunity (pre-existing, passed on by the mother since birth) in overdrive mode leading to a cytokine storm in more severe cases.

The adaptive immunity, which is more potent, long-lasting and much-desired, is suppressed. The challenge is to develop therapeutic strategies for maintaining an optimal balance between the two, so as to halt viral replication and promote the destruction of virus-infected cells.

The infection rates and clinical severity of Covid-19 patients are highly variable across populations. As of June 16, more than 8.15 million cases and over 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 nearly 59 lakh tests and only 7.0 deaths per million population.

For such a densely-populated country and despite the recent spike due to opening up, these figures are remarkably low as compared to hotspots in Europe and the US where up to 15% cases and significantly higher fatalities have been reported.what is even more remarkable is that there are relatively few severe/critical cases in India and the mortality rate out of the total positive cases is very limited (less than 3%).

The observed population-specific heterogeneity in infection rates and clinically different patterns (morbidity and mortality) are due to two factors namely, virus virulence and host-susceptibility, both of which are interdependent and together result in the manifestation of the infection.

A virus that is virulent in one setting could be innocuous in another. On the other hand, host-susceptibility is dependent on the genetic diversity of genes that control immune responsiveness in a population. The latter is shaped by diverse microbial and geographical pressures, which are a hallmark of evolutionary selection and immunity to novel pathogens.

Once the peak is reached, the virus may continue to replicate though at lower levels in the face of immune recovery, as reflected in the percentage of recoveries.

It is noteworthy that nations with a recovery rate of 70% and above (China 94.3%, South Korea 90%, Germany 91.3%, Scandinavian countries 82-95%, Italy 71%) have all been able to reverse the trend with significantly reduced number of new cases and daily deaths. The so-called smouldering infections may lead to more asymptomatic cases which can improve immunity. Government responses should continue to focus on detecting and isolating infected people with symptoms.

More good news comes from New Zealand, which became the first country with zero active cases, while neighbouring Australia, with a recovery of over 92%, has also resumed normal activities.

The recovery rate in India is almost static at 48% since June 1 due to greater public activity, leading to a daily spike in the number of new cases. This is shifting the recovery further ahead by weeks, maybe months. The focus has to be on slowing spread of the virus. To achieve this, novel strategies will have to be developed that may vary from state to state. The target should be to achieve recoveries upwards of 70% as early as possible.

India’s situation is not very different from that of Russia and Brazil, both having reached high numbers and still reporting significantly high infection rates daily.

The big question that everyone is asking is whether we are expecting the peak in India along with subsequent decline in infection rates anytime soon. It is conceivable that in such a vast country, no one single peak can be expected and the much-anticipated decline in numbers will differ in different regions.

Currently, it is apparent that many more people will get infected and self-help groups must step forwards to make Covid-19 a people’s 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 the contact levels to about 74% and this can help mitigate considerably the spread of the virus which could lead to a decline in cases in the coming weeks. The real challenge for us would be to focus on keeping the mortality rates low.

Understanding host-susceptibility to the SARS-COV-2 virus is a key step towards 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 patients who recover are able to develop long-lasting immunity against reinfection and whether those reinfected will develop a milder form of the disease compared to those who were previously not infected.