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Numbers behind different COVID-19 vaccines



By M. C. M. Iqbal

The vaccines against COVID-19, available today, are based on different strategies and come with different numbers to indicate their performance. Many of us wish to know if one vaccine is better than the other. Two concepts underlying the performance of the vaccines are efficacy and effectiveness. The Pfizer-BioNTech vaccine has an efficacy of 95 percent, the Moderna Vaccine is 94.5 percent and the Russian made Sputnik vaccine is over 90 percent. Does this mean some vaccines are better than the other? The short answer is no. All the approved vaccines are equally good. So, let us look at what these numbers mean.

These numbers refer to statistical calculations to interpret the results of vaccination trials conducted by the manufacturers of vaccines, following a prescribed format. The method of calculation was developed over 100 years ago by two statisticians, who published their results in the Proceedings of the Royal Society of Medicine in 1915. They, Major Greenwood (Major is his first name and not a military title) and Udny Yule, were tasked with interpreting the results of immunization of British soldiers against typhoid and cholera, who were fighting in different regions of Europe and Asia favourable to the development of cholera epidemics. In a paper stretching over 82 pages, the authors developed the theoretical and mathematical background for calculating the efficacy of vaccines.

This article seeks to explain to the lay reader what these numbers imply and to bring out the differences between efficacy and effectiveness of a vaccine.

Efficacy and effectiveness

At first sight these two terms appear to be synonyms. However, in the world of vaccines and medicine, these two terms are not the same. Efficacy of a vaccine is how it performs under ideal and controlled conditions in a clinical trial (see below). During clinical trials, the outcome of vaccination is compared between a group of vaccinated people and another group given an inactive form of the vaccine (called a placebo). The effectiveness of a vaccine is how the vaccine performs in the real world – that is after the vaccine is approved by the regulatory agencies and you and I are vaccinated.

The efficacy of a vaccine is measured by the manufacturers under ideal conditions in a clinical trial where criteria are specified for selecting and excluding volunteers. These criteria are usually age groups, gender, ethnicity, geographical location and socio-economic standing. If the criteria are specific, then the effects of the vaccine or drug would not be applicable across the population. For example, if the COVID-19 vaccines are not tested on children below 18 years, then the approved vaccine cannot be used on children.

The effectiveness of a drug or vaccine is a measure of how well the drug or vaccine performs in real life, in a diverse population: Fitness geeks and couch potatoes, housewives and nurses, and farmers and office workers. Effectiveness is of relevance to the medical community and healthcare authorities who are treating the patients. Thus, studies on effectiveness would look at to what extent the vaccine is beneficial to the patient to prevent infection.

One may ask, why not simply look at the effectiveness of the vaccine? This is because if the participants in an initial trial of the vaccine are not carefully controlled, then it is difficult to interpret the outcome of the trial. We have many characteristics, which can potentially interfere with the outcome of a trial testing a vaccine. The person volunteering for the trial could be young or old, pregnant or not, a marathon runner or an average person and smoker or non-smoker. Thus, the volunteers selected for the trials are very similar within their groups with many criteria to exclude persons who could confuse the results (for example, an unhealthy person with other diseases would be excluded).

Efficacy of a vaccine asks the question ‘Does the vaccine work under ideal conditions?’ On the other hand, a study on the effectiveness of the same vaccine asks the question ‘Does vaccination work in the real world?

Clinical trials

Under normal circumstances, vaccines take many years of research and testing to be approved. The COVID-19 pandemic was unprecedented, and pharmaceutical companies embarked on a race against time to produce safe and effective vaccines. The genome of this coronavirus, which was discovered by Chinese scientists, in January 2020, was a major contribution to the development of the vaccines. At the moment there are 94 vaccines being tested on humans in clinical trials, 32 of which have reached the final stage of Phase 3 testing.

To obtain approval for a vaccine, the vaccine manufacturers go through a prescribed process to ensure that the vaccine is safe. All the countries have a national drug approval agency, who should approve the use of a drug or vaccine in that country. The Food and Drug Administration (FDA) in the United States is an important regulatory agency, which has stringent criteria to approve medicines and drugs. In Sri Lanka, it is the National Medicines Regulatory Authority. COVID-19 vaccines are also assessed and approved by the WHO.

Initially, the vaccine is tested on cells in the laboratory and then given to animals, usually mice or monkeys. After this, if the mice or monkeys are happy, human volunteers are recruited to conduct the clinical trials, which is done in three phases. In the first phase, the vaccine is tested on a small group of people to determine the safety, dosage and ability to stimulate our immune system. If this is confirmed, the vaccine then moves into the Phase 2 stage where the safety of the vaccine is tested on hundreds of people who are split into different groups. Once these trials are successful, the vaccine moves to the final Phase 3 trials. Here thousands of people are recruited as volunteers. For the Pfizer-BioNTech vaccine there were over 40,000 volunteers, above the age of 16, from different countries. This trial is more comprehensive, with the volunteers belonging to different age groups, physical fitness, ethnicities and geographical locations. The volunteers are divided into two groups. One group gets the real vaccine while the other group gets a fake vaccine or placebo (the syringe has just water). The volunteers would not know if he/she is getting the vaccine or a placebo and neither do the nurses and doctors giving the vaccine. This is called a double-blind clinical trial. Thus, no one knows, except those conducting the trial, who was vaccinated with what.

After some time, the volunteers, who fell sick with the coronavirus, are PCR tested to confirm if they are COVID-19 positive. The scientists will be on the lookout for any side effects of the vaccine; if they find any cause for concern the trial can be stopped temporarily to conduct investigations and remedy the problem. If the scientists are not satisfied, the trial would be abandoned. Once the results are in, the calculations are done, and all the details are submitted to the regulating authorities. The regulators would ask the manufacturers more questions and once they are satisfied, approval is given to manufacture and market the vaccine. To accelerate the process, such as now during the COVID-19 crises, Phase 1 and 2 may be combined and run in parallel.

Calculating efficacy

The calculations involved are quite simple once the data is collected. Let us assume that 50,000 volunteers were recruited for the vaccination trial. Half were given the vaccine and the other half a placebo. Let us assume that of the 25,000 who received the vaccine, 10 persons were infected, and of the other 25,000 who received the placebo, 200 were infected. Although the numbers of people infected are small, those in the placebo group are 20 times larger (see Table). The researchers are concerned with the relative risk between the groups. This is called the efficacy of the vaccine.

The risk of infection is calculated as follows.

What is the difference in the risk of infection between the vaccinated group and those who got the placebo? From the table this is, 0.80 percent – 0.04 percent = 0.76 percent.

Thus, the vaccine reduced the risk of infection by 0.76 percent, which looks quite small. This is what would happen if we are vaccinated. To understand this in terms of the risk of infection, if none were vaccinated, we look at the ratio of the Reduction in Infection (0.76 percent) to the Risk of infection (0.80 percent – those who got the fake vaccine). This is the Vaccine Efficacy (VE).

VE percent = Reduction in infection ÷ Risk of infection = 0.76 ÷ 0.80 = 95 percent

If this is still confusing, let us see what it means in a population of 100,000 persons who are vaccinated with a vaccine of 95 percent efficacy, and exposed to the virus. From the table above, the risk of infection for the vaccinated population is 0.04 percent, which translates to 40 persons (0.04 percent x 100,000). That is, we can expect that 40 persons would fall ill with an infection by the coronavirus and the rest of the vaccinated people may not develop an infection at all or develop an asymptomatic infection (you are infected but do not show symptoms) or get a mild disease.

(This example of calculating Vaccine Efficacy is adapted from an article by Dashiell Young-Saver in the New York Times of December 13, 2020, where the above calculation is explained in detail for students.)

What does efficacy mean?

The efficacy of a vaccine refers to two aspects. The first is how many of us are protected by the vaccine if we are exposed to the virus; this is given by the percentage. The vaccine also refers to different disease conditions it is capable of preventing. This could be causing an infection, mild disease, severe disease, hospitalisation, or death. This information can be found if one looks carefully at the statements issued by the vaccine manufacturer and regulatory agencies. For example, the statement by Pfizer-BioNTech states: Pfizer-BioNTech COVID-19 vaccine, BNT162b2, was 91.3 percent effective against COVID-19 (symptomatic cases of COVID-19), measured seven days through up to six months after the second dose. The vaccine was 100 percent effective against severe disease as defined by the US centres for Disease Control and Prevention (CDC), and 95.3 percent effective against severe disease as defined by the US FDA.

The efficacy of a vaccine (VE) is the relative reduction of being infected, if we are vaccinated, compared to the placebo or unvaccinated group. If the vaccine is perfect, then the risk of being infected is totally eliminated, so that VE = 1 or it is 100 percent. On the other hand, if there is no difference in the number of people infected between the two groups, the vaccine has no efficacy, or it is zero. Even with a perfect vaccine, our capacity to acquire an infection is determined by our age, health and immunity status.

In short, efficacy is a statistical measurement based on clinical trials of the vaccine’s ability to prevent infection. The volunteers taking part in the trials are not a perfect sample or representative of the real world (for example, children and sick people do not take part). Is there a lower limit for the efficacy of a vaccine to be accepted? Under the present circumstances, the FDA said it would consider granting emergency approval if the vaccines showed even 50 percent efficacy; the vaccines that have received approval now show an efficacy of over 90 percent.


The effectiveness of the vaccine tells us how well the vaccine is performing among the population, in the real world, to prevent infection. The effectiveness of the vaccine depends on the impact it makes on society. After vaccination our immune system is primed to combat the coronavirus, reducing the multiplication of the virus in our body. This will gradually slow down the spread of the virus as more and more people are vaccinated. In other words, it is important that most if not all the people are vaccinated to have a large impact on the spread of the virus in society. Good examples are the smallpox vaccine, which completely eliminated the smallpox virus, and the polio vaccine, which has almost wiped out the polio virus except for a few small pockets in Pakistan, Afghanistan and Africa. Thus, the effectiveness of a vaccine looks at the medical and societal importance of the outcome.

Here is the above in a nutshell. The percentage numbers given with a vaccine refers to its efficacy – its ability to prevent an infection developing into a serious condition, determined under controlled clinical trials. Vaccines do not prevent infection – they prevent the infection from developing into a severe disease. Once we are vaccinated, our immune system is activated. If we are infected by the coronavirus, the virus has a small window of time to multiply, before it is eliminated by our immune system. This means we can release virus particles from our body, but much less than if we were not vaccinated. The message is we should get vaccinated with the first available vaccine and still wear our masks when going outside, even if we are vaccinated. The chances of ending up in a hospital is low and the chances of ending up in the ICU is very low. There is always a chance.

‘Tis impossible to be sure of anything but Death and Taxes (Christopher Bullock, 1716).

(M.C.M. Iqbal is Associate Research professor, Plant and Environmental Science, National Institute of Fundamental Studies, Hanthane Road, Kandy, and can be reached at


Zimmer, C. New York Times Nov. 20, 2020. Two companies say their vaccines are 95 percent effective. What does that mean?

Haelle,T. Association of Health Care Journalists. October 22, 2020. Know the nuances of vaccine efficacy when covering Covid-19 trials.

Greenwood, M., & Yule, G. U. (1915). The Statistics of Anti-typhoid and Anti-cholera Inoculations, and the Interpretation of such Statistics in general. Proceedings of the Royal Society of Medicine, 8 (Sect Epidemiol State Med), 113–194.

Food and Drug Administration, US Department of Health and Human Services.

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Mr. President, please let this be a turning point!



By Rohana R. Wasala

When I pen these words, most Sri Lankans are still sleeping. I am ahead of them and awake. That is because of the time zone difference between where I live and Sri Lanka, my country of birth. As usual, as the first thing I do in the morning, particularly these days, I glanced at the headlines in The Island epaper, and was depressed to read the banner headline “Ratwatte remains a state minister despite resignation over running amok in prisons”, with the following underneath it:

“State Minister of Prison Reform and Rehabilitation Lohan Ratwatte yesterday told The Island that he had informed President Gotabaya Rajapaksa that he would step down immediately from his post as the State Minister of Prisons. However, he will continue to be the State Minister of Gem and Jewellery Industries”.

Having earlier read and heard over the media about Lohan Ratwatte’s alleged escapades in prisons on Sunday (12) night, I have been eagerly waiting to read a newspaper headline like “Deputy Minister remanded; a good start to meeting challenge to rule of law”, for I expect nothing less from President Gotabaya Rajapaksa. As a disciplined and determined executive, with a military background, he, I assume, tries to handle the toughest cases with the strictest adherence to the law. He appears to rely on the ministers and the government servants, serving under him, to follow his perfectly lawful commands in a spirit of military discipline, mutatis mutandis, in the context of civil government. Whatever the likely or actual response to the extremely embarrassing deputy-ministerial episode (not the first involving LR), it should be of a kind that contributes to a restoration of the fast eroding public faith in the hoped-for Gotabaya rule. The Island editorial of Thursday (16) under the arresting heading “Arrest them” offers sound advice. I drew some solace from that. For I realised that there is at least another person of a like mind.

I was even more shocked and disappointed by the Commissioner General of Prisons Thushara Upuldeniya’s attempted absolution of the Deputy Minister. According to the online Lanka C News (September 16), the Commissioner has said that the Minister visited the prison to discuss pardoning some prisoners and that the he has the right to visit the prison to discuss with the inmates at any time of the day. The Commissioner might be technically right, but I am doubtful about the lawfulness of what the Minister has done, especially in his alleged inebriated state. Upuldeniya was handpicked by the President for the extremely demanding job. His coming to the defence of LR was a bolt from the blue to the innocent peace-loving law abiding citizens of the country who have been for decades persecuted by the persistent menace posed by the unholy alliance between criminals and some jailors and a handful of politicos providing together an impregnable bulwark for the first.

However, since the case hasn’t yet been verified or investigated, we don’t know for sure whether the Deputy Minister is guilty of going berserk under the influence of liquor as alleged. As a person embroiled in politics, he could be a victim of some calumnious effort of his detractors, and we must be cautious in passing judgement on him. But again, as he, who has a previous thuggish reputation, has virtually accepted guilt in this case by tendering his resignation, citizens are justified if they expect, as I do, a tougher reaction from the President.

At this moment we should anticipate a presidential response different from the mild rebuke “Anthimai!” (equivalent of a sarcastic “Great!”) that the then President Mahinda Rajapaksa greeted the hospitalised Labour Minister Mervyn Silva with, on December 27, 2007. (I eagerly hope that the President’s deterrent reaction would be known before this reaches The Island readers.) The latter was admitted to hospital after being given a taste of his own medicine following a rowdy interference he committed with the work of a news editor by the name of T.M.G. Chandrasekera at the state-owned Rupavahini TV station over not giving enough coverage as he alleged to a public event that he had organised in Matara the day before. Though very close to MR, he was not an elected MP; he was only a national list MP from the SLFP that MR led. In any case, it was inexcusable that he conducted himself the way he did, for what he did was bound to reflect badly on the President himself. The other employees of the TV station, angered by the uncouth highhanded behaviour of Mervyn Silva, forced him and his notorious sidekick, suspected drug trafficker Kudu Nuwan or Lal or someone (I am not too sure about these trivial details now) to a room and held them there, handling them roughly. Mervyn Silva was heard pleading : “I will tender an apology if you say I have done wrong”. He had. The workers were providing manual proof as best they could.

Mervyn Silva was beaten up right royally, and bundled into his prestigious ministerial Pajero and was briskly driven away to hospital safety. The state Rupavahini telecast the proceedings live for the whole world to see in repeated ‘news flashes’ most of the day that day, as my older readers might clearly remember. It was a sort of news carnival for the wrathful Rupavahini broadcasters and for the scandalised viewers. While watching the scenario live, I convinced myself that President Mahinda Rajapaksa would kick his you-know-what-I-mean within the hour, or at least after his discharge from hospital. To my utter disgust and disappointment, nothing like that happened. The fellow flourished for another eight years under MR’s wing until he betrayed him utterly in 2015, after having abused his well-known humaneness and his reluctance to abandon people who have helped him in the past. Lately, Mervin seemed to try to cozy up to the boss he so treacherously let down; but MR’s brothers have saved him from his erstwhile unequal friend.

I personally believe that we are not going to see such wretched characters protected under President Gotabaya Rajapaksa during the remainder of his term.

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20-year war swelled arms industry coffers



Five US arms producers made US $ 7 trillion, equivalent to 350 years of Sri Lanka’s annual foreign earnings, at US $ 21 billion per year from wars to counter 9/11 attacks

By M.M Zuhair, PC

The world’s most powerful country, the United States, remembered the 20th anniversary of the 9/11 attacks last Saturday while Sri Lanka, supporting the remembrance, expressed solidarity with the US. Significantly, the truth that emerged from the post-9/11 wars; in terms of deaths, of refugees and of those who benefited from the wars that the US-NATO launched in response to the attacks, is absolutely shocking when compared with the figures relating to 9/11!

The US-NATO counterattacks appear, unbelievably, more catastrophic than the 9/11 attacks, blamed on US-educated Saudi businessman Osama bin Laden and his Al Qaeda. In four coordinated attacks, 19 hijackers, working in four groups, wantonly targeted the Twin Towers and the Pentagon with hijacked planes, leaving all 2, 977 persons dead. According to Newsweek, as of April 2021, the subsequent US-NATOled counter-attack invasions left an additional 7,442 persons from the US and allied forces, plus American contractors, dead. The invasions took away exactly two and a half times more US lives than those lost on 9/11! “I don’t know why!” would have been the likely response of Sri Lanka’s famed singer, the late Sunil Perera!

What about the destruction on the side of the attacked? No clear record, or estimate, of the number of Afghans, including civilians, killed in the US-led war, is available from Afghan sources, but Western estimates place it at between 1/4 to 1/2 million deaths! According to Nicolas Davies, writing for Mint Press News, the Bush-Blair aggression in Iraq, without Security Council approval, caused an estimated 2.4 million Iraqi deaths!

Davies wrote, “But no crime, however horrific, can justify wars on countries and people who were not responsible for the crime committed,” quoting former Nuremberg prosecutor Benjamin Ferencz of the United States.

The US Watson Institute of International and Public Affairs has disclosed 30,177 suicides among US services personnel and veterans who returned after war assignments post 9/11, citing, among others, difficulties in re-integrating civilian life. In combat, 30,177 suicides versus 7,442 deaths are shocking figures, indeed! Today elements within the Taliban, after confronting 43 years of wars and foreign occupation are struggling to reintegrate back to civilian life!

What about the refugees and the displaced? Studies by the Watson Institute have also disclosed that the invasion of Afghanistan had resulted in 2.61 million refugees, 1.84 million internally displaced persons (IDPs) and 330,000 asylum seekers totalling 4.78 million! The total number of refugees and IDPs in Iraq were 3.25 million and in Syria 12.59 million, all of them a result of the US-led invasions post 9/11!

Challenges before the countries that Western powers invaded, killing over an estimated three million, rendering as refugees several millions with many more millions internally displaced, all of whom had nothing to do with the 9/11 attacks, are many. The most urgent priority would be rebuilding the lives of the surviving millions, and in addition, in the case of Afghanistan, preventing its economy from crashing!

Of the refugees, 1.3 million are in Pakistan, two million in Iran, 3.5 million in Turkey and the balance in Europe! They are the innocents dehumanised by the Bush-Blair aggressions when they could have easily captured bin Laden if they had subcontracted the job to the Israeli Air Force and the Mossad. Bush and Blair were fully aware of how on July 4, 1976, the Israelis successfully launched a counter-terrorist hostage rescue mission at the Entebbe airport in Uganda rescuing 102 out of 106 Israeli hostages.

If bin Laden was in fact the mastermind of 9/11, that ‘changed the world’, surely nothing prevented his capture to recover invaluable intelligence of his operations and network! It would soon be evident as to why the US did not want to capture bin Laden when the unarmed man was in the hands of the US marines and did nothing to countervail!

It is noteworthy that of the 19 hijackers, none were from Afghanistan! Importantly, the Taliban condemned the 9/11 attacks, soon thereafter, which was ignored by Western powers! The Taliban’s offer thereafter to facilitate the Organisation of Islamic Cooperation (OIC) to put Osama bin Laden on trial in a neutral country was also rejected by the US. But then the object was war and wars as long as possible and not capturing the enemy, which would otherwise lead to the US having to finish off the wars, to the detriment of the arms industry!

Felix Salmon, in a piece dated September 11, 2021, in Axios, says that after 9/11, defence contractors made $7.35 trillion (equivalent to Sri Lanka’s annual foreign revenue for 350 years at US $ 21 billion per year!) The vast majority of this money, he says, came from the Pentagon. The top five US arms manufacturers who benefited from 9/11 are Lockheed Martin, Raytheon Technologies, Boeing, Northrop Grumman and General Dynamics.

Countries that manufacture arms and explosives include the USA, the UK, France, Germany, Israel, Russia, China, Australia, Japan, India, South Korea, UAE, Norway, Sweden, Canada, Turkey, Singapore, Brazil, Spain, Italy and Ukraine. They are the beneficiaries of wars fought in other peoples’ lands, often based on false accusations.

Many foundations, fronts and forums, are allegedly funded by the arms industry. Substantial sections of the Western media are also at the forefront, beating war drums. People believe the conversations marketed through electronic and print media, with no time to cross-check fake stories often planted by those with vested interests. Very few journalists, in third world countries, have time or the means to cross-check stories. Hate and prejudices are built up over time against the victims of wars and conflicts. ‘I don’t know why!’

They have amongst war veterans, academics and other so-called experts who create false perceptions, hatred and conflicts amongst people in otherwise peaceful countries. People who resist are portrayed as extremists and terrorists. Ultimately, countries that need peace, harmony and unity to revive their economies and the quality of life of their people, find themselves embroiled in worthless conflicts. These conflicts are engineered by agents who mislead those in power and authority, probably getting kick-backs from the agents of these powerful forces, who hop around in vulnerable countries.

But there are exceptions. They are not known nor are they even duly heard. Barbara Lee in 2001 was the only member of the US Congress to vote against the War on Terror. On September 14, three days after 9/11, Lee voted against the 2001 ‘Authorisation for Use of Military Force’ (AUMF) that started the 20-year war in Afghanistan, even before any credible investigations into 9/11 could even begin! Twenty years later, on August 15, 2021, the US-NATO forces abandoned an economically collapsing Afghanistan!

Lee said on September 9, 2021, “Each hour, taxpayers were paying US $ 32 million for the total cost of wars since 2001 and these wars have not made the Americans safer or brought democracy or stability to the Middle-East. For too many years we have outsourced our foreign policy to the Pentagon. I cast the lone vote in Congress against the authorisation because I feared it was too broad, giving the President the open-ended power to use military force anywhere, against anyone.”

(The writer can be reached at

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Ivermectin and Covid: no time to lose and lives to save



By Prof. Saroj Jayasinghe,

MBBS, MD (Colombo), FRCP (London), MD (Bristol) PhD (Colombo), FCCP, FNASSL

Consultant to the Faculty of Medicine

Sabaragamuwa University of Sri Lanka.

Former Professor of Medicine, University of Colombo

It is with a degree of reluctance that I am stepping into the controversy relating to Ivermectin use in COVID. Unknown to many, the pros and cons of Ivermectin in COVID have been discussed in private forums of physicians, academia and doctors from 2020. It has been in the international media ever since laboratory studies in Australia showed that the drug inhibits the growth of the virus. However, the public in Sri Lanka became more aware of the controversy recently, when a confidential letter sent to an official of the Ministry of Health appeared in the social media. I had written this in June 2021 as an individual professional after several months of raging controversy among professionals. It was about treatment of COVID, and I firmly believe vaccination is the best option to prevent the illness. One reason for the very cautious approach of not approving the use of Ivermectin in the West could be because anti-vaccine groups are promoting it as an alternative. Sri Lanka has no such problems, and our population is willingly getting vaccinated.

Proposals to use Sri Lanka as a large study area as a clinical trial or as an observational study were made as far back as early 2021. I understand a clinical trial has begun in patients admitted with COVID, after considerable delays due to procedures related to clinical trials. Such studies are scrutinised by independent ethics committees, the drug must be approved by the National Medicinal Drugs Authority, and the study must be registered in an entity that makes is publicly available for anyone to read about it. This study will at least take another few weeks to months to yield results.

Most discussions in Sri Lanka Centre around the question whether the evidence to prescribe Ivermectin in COVID-19 is strong or inconclusive. One group says there is inconclusive evidence to use Ivermectin while another group says there IS sufficient evidence. As with many issues, this is not black or white but shades of grey, i.e. there are grades on the ‘strength of evidence’ from the field of Evidence Based Medicine (EBM). A parallel in the legal field is when we say that the evidence is ‘beyond reasonable doubt’ or there is ‘proof of the crime’, vs. circumstantial evidence.

Let us assume that using the principles of EBM we find that the evidence to use Ivermectin in COVID is ‘inconclusive’. Such a dilemma is very relevant to a situation where a decision is needed immediately, but the stakes are high. In other words, how would doctors decide to treat in a situation when the evidence for efficacy of a drug is inconclusive, but the stakes are high? Let me share an example.

Imagine a doctor who sees a very ill-looking patient with features of a serious infection (e.g. high fever, vomiting and body aches). She or he requests tests to identify the cause of the illness and the bacteria that may be causing the illness. In such an instance, should the doctor wait till the reports of the tests (e.g. culture reports) are available before treating? If a decision is made to treat immediately, the doctor does not have the ‘strength of evidence’ on the cause of the illness. However, if treatment is delayed until the reports arrive in two days the patient may be dead. This hypothetical example highlights a common dilemma: How do doctors balance between reliance on strength of evidence vs. taking an immediate decision when the evidence is inconclusive. This is best addressed by theories of decision-making and is a question very familiar to practicing doctors.

Now I will demonstrate the parallel with Ivermectin. In the case of ivermectin let us assume that the current evidence for its efficacy in COVID is inconclusive. However, the stakes are very high because COVID is currently raging, hundreds are dying, and there are no alternative drugs to treat early disease. Furthermore, Sri Lanka needs to bridge only a short vulnerable period of 4-6 weeks during which time our vaccination programme would become effective.

Let us assume that doctors begin to prescribe Ivermectin for treatment and prevention of COVID, for the next 4 to 6 weeks, despite the inconclusive evidence. There are two possible key outcomes:

Outcome 1: Future research confirms that it is effective, and it would contribute to saving many lives.

Outcome 2: Future research shows that it is ineffective, and we would have wasted money on the drug. Therefore, Ivermectin could either save lives or waste money. Even the money wasted is miniscule because the cost of a course of Ivermectin is less than Rs 200.00 (i.e. less than one US dollar)! Is it safe to use over the next 4 to 6 weeks? We know it is a very safe drug that has been used for almost 40 years. It is used in mass scale by the WHO to eliminate ‘River Blindness’ and is in their Essential Drug List.

A combination of other factors add support to the decision to prescribe Ivermectin.

1. Evidence is evolving, and studies are in progress. Therefore, conclusive evidence may emerge to confirm its efficacy.

2. There is laboratory (in vitro) evidence that Ivermectin is active against the COVID-19 virus.

3. It’s easy to give (tablets and not injections).

4. Currently there are no effective drugs in Sri Lanka to treat early COVID or prevent it.

5. Certain regions in India and South American countries are using Ivermectin to treat and prevent COVID-19


Therefore, my humble question is, should doctors in Sri Lanka consider whether to use Ivermectin to treat or prevent COVID-19? We need this only for 4-6 weeks. During this period, rates of COVID are likely to increase due to the very rapid transmission of Delta variant. We have no time to lose, nothing to lose, and lives to save. There is no time for clinical trials. Those who wish to embark on trials to wet their thirst for more evidence are welcome to do so. By the time the results of a new trial are available the horse would have bolted, and hundreds would have died.

My suggestion is for patients to ask your doctors about Ivermectin. You have a right to do so. Doctors are divided on the issue because of their sincerity to the views they have about science, scientific evidence, and decision-making. Please do not assume that there is a conspiracy against the drug in Sri Lanka! I can vouch for the honesty of all the doctors who are having different views on the topic. This is a disagreement between professionals who have diverse views, and we seem to have dug into our lines of defence!

The Ministry of Health has allowed the use of Ivermectin under the direction of a doctor. A range of doses for treatment and prevention is available at a group working in the UK. The opinions I have stated here are my own independent views and not in any way linked to the institutions I am affiliated to.

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