“We need to be vigilant when reopening the borders”

Interview: Dr Deoraj Caussy, Independent Epidemiologist

“A second wave is not only unavoidable, but it is a natural course of many respiratory viral diseases”


Will the reopening of the country to international travel once it becomes effective put the country and its population at risk and bring in its wake a second wake of Covid-19? In view of the growing apprehension of the population about the risks involved, we have sought the views of Dr Deoraj Caussy, who currently practices as an Independent Epidemiologist (Integrated Epidemiology Solution at drdeorajcaussy.com), after a long career working in various laboratories, including with the US Centers for Disease Control. He joined WHO as an epidemiologist and retired as Regional Epidemiologist in Asia, based in India. His response to the possibility of a second wave that “we cannot lower our guard”, he says, draws from our current working hypothesis, based on statistical modelling, which predicts a herd immunity of 60-80% for halting the pandemic. “But we know from the epidemics around the world that at the most between 5-10% of the population of a country has been infected. With the movement of goods, services and human beings in an interdependent globalized world, it stands to reason that a second wave is looming round the corner.”


Mauritius Times: Coronavirus is far from over in many countries. Some countries are still dealing with large epidemics, others that have controlled the virus fear a “second wave”. New Zealand, has seen its first cases after 24 days without coronavirus. Beijing is facing an outbreak after 50 virus-free days. We have had no local case for the last 86 days. There is therefore no reason to fear a second wave, right?

Dr Deoraj Caussy: We live in a global village in which the world is interconnected. The compelling evidence to date shows that the virus will spread as long as there are susceptible population and appropriate environmental conditions.

The virus continues to spread worldwide and has already infected over 14 million persons globally. China and other countries like Germany and France are seeing second waves.

The second wave is expected as long as the world and a region of a country have not been synchronously infected to build a herd immunity level of about 60-80% required to naturally halt the virus spread.

* What is a “second wave” anyway, and what are the things that should happen for us to meet the criteria for a second wave?

A second wave is phenomenon whereby the epidemic resurges after an initial outbreak. It happens because an equilibrium in the triangle of interaction among the population, the virus and the environment has not been reached or is shifted in the favour of one factor: the number of susceptible persons in a population can drive an epidemic, as can the mutation or adaptation of the virus or an environmental factor like humidity or temperature favouring the spread of the virus.

* Is a second wave inevitable?

A second wave is not only unavoidable, but it is a natural course of many respiratory viral diseases like human influenza and SARS-CoV-2 viruses. Our current working hypothesis, based on statistical modelling, predicts a herd immunity of 60-80% for halting the pandemic.

But we know from the epidemics around the world that at the most between 5-10% of the population of a country has been infected. With the movement of goods, services and human beings in an interdependent globalized world, it stands to reason that a second wave is looming round the corner.

* One argument against a deadly second wave is that viruses become less dangerous as they evolve, to better infect people. But the second phase of Spanish flu a century ago was deadlier than the first. And how bad could a second wave be?

Currently, there are no a priori reasons to believe that the SARS-CoV-2 virus will be less dangerous or deadlier since this is a new virus and we have not observed it for long enough. We can extrapolate from Spanish, Asian, Hong Kong and H1N1 influenza pandemics. In these past pandemics three main patterns were seen: a mild first wave followed by severe second wave; a severe first wave followed by a mild second wave, or a mild first wave followed by a mild second wave. Whether SARS-CoV2 will follow the influenza model or its own remains to be seen. For these reasons we cannot lower our guard.

* Even though there have been no local case of Covid-19 detected in Mauritius since 26 April 2020, those that have been detected are imported ones. Lots of Mauritians are therefore apprehensive about the reopening of the country to the outside world given the risks involved, although they do understand that this will have to be done sooner or later. What would be the safest way to go about reopening the country?

It is a perfectly normal reaction to be apprehensive: we are like scalded cats dreading cold water. But cats and water do not mix, whether cold or hot. Health and economic development are interdependent; a wealthy population is a healthy population and a healthy population is an economically productive population.

For sure we need to be vigilant when reopening the borders, and our priorities should aim at 1) ensuring our surveillance is state-of-the-art to detect both symptomatic and asymptomatic cases so as to prevent re-seeding of the virus in our territories, 2) maintaining a well-performing and resilient health system to take timely and proper medical care of infected patients to mitigate morbidity and mortality, 3) protecting the vulnerable groups, including the frontline workers, and 4) promoting, supporting and maintaining the already proven public health measures of social distancing, wearing of masks and abundant use of disinfectants to break the chain of transmission.

* We would assume that the same or stricter health protocols in terms of tracking, quarantine and treatment would be put in place once the country is reopened to the outside world, but do you fear that the demands on the local health authorities would be much too heavier than it can manage once international travel starts picking up?

We have to learn from and remedy our glaring initial mistakes of failing to be pro-active in timely closing of the border in the face of an impending epidemic and of excluding asymptomatic cases in the initial surveillance. This time we have to carefully follow and monitor the virus and wipe it at the outset rather than allowing it to seed and transmit at community level as was the case during the first wave: a single spark of fire may ignite a whole forest if not controlled in time, similarly a single undetected and uncontrolled case may set up a wave of second epidemic.

As a seasoned epidemiologist with extensive experience in managing pandemics around the world, I observe frequency and pattern of events to search for cause and control measures. The epidemiological observations indicate that implementation of timely public health measures would have averted 10 mortalities and countless stress and inconvenience to the population.

To remedy all these shortcomings, we have to use state-of-the-art and internationally validated methods and protocol. A complete pandemic preparedness plan with activities for all phases of the pandemic including post-pandemic is a critical public health must have for any authority involved in successfully controlling the covid pandemic.

* More than 140 teams of researchers around the world are racing to develop a safe and effective coronavirus vaccine. But these are said to normally require years of testing and additional time to produce at scale, but scientists are hoping to develop a coronavirus vaccine within 12 to 18 months. How close do you think we are to developing that vaccine?

Since vaccines will be used to immunize billions of people, the development of vaccine has to conform to international norms in both technological and ethical domains.

Currently, there are close to 300 vaccines that are being tested in a race against time, scientific and commercial gains. However, we are far from a vaccine in the immediate 12 months.

* Could it be said that we’ll only be out of danger once a vaccine has been developed?

Absolutely not. There are three main huddles to be overcome once a vaccine is developed: 1) we have to ensure that the vaccine confers long term immunity; that is only possible by observing the vaccinated subjects over subsequent epidemics, 2) the vaccine may not be affordable for the developing countries and the most vulnerable like the old, poor and socially disparate groups 3) the vaccine has be socially acceptable by all groups including the high risk groups that are super-spreaders.

* David Nabarro, professor of global health at Imperial College, London, and an envoy for the WHO on Covid-19 recently said that ‘humanity will have to live with the threat of coronavirus for the foreseeable future and adapt accordingly because there is no guarantee that a vaccine can be successfully developed’. What’s your take on that?

David Nabarro is an ex-colleague of mine from WHO and he echoes my sentiments in my previous response.

Vaccines are not panacea. Look at polio vaccine, we have effective vaccines for years now, yet despite the massive global efforts of polio eradication and billions of dollars spent, we still have polio endemic countries to this day.

Take another example: the measles vaccine which has existed for years, yet here in Mauritius we see outbreaks of measles due to inadequate vaccine coverage.

Our best vaccine remains the classic public health measures of surveillance, testing, contact tracing and isolation, and breaking the chain of transmission by social distancing, wearing of masks and environmental management.


* Published in print edition on 21 July 2020

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