Opinion

Numbers behind different COVID-19 vaccines

Published

5 years ago

2021/08/18

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.

Effectiveness

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 iqbal.mo@nifs.ac.lk)

References

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. https://healthjournalism.org/blog/2020/10/know-the-nuances-of-vaccine-efficacy-when-covering-covid-19-vaccine-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. https://www.fda.gov/media/139638/download

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Opinion

A paradox of history

Published

17 hours ago

2026/02/16

Thilina Walpola

Shakespeare

There seems to be a striking similarity between ancient Greece and modern Britain. Both countries remain paradoxes of history. Greece was a small city state constantly at war with neighbouring countries. It did not have a big army, but it had considerable sea power. However, Greece was a leading state over the whole of the Mediterranean. In fact, Greece was once a super power in the Western world.

Britain was very powerful in the 19th century. British justice was administered in Africa, India and Ceylon. British factories flourished in many countries and schoolchildren started reading R.L. Stevenson’s ‘Treasure Island’ and the works of Rudyard Kipling. What Ralph Waldo Emerson said in the 1850s is still valid today. He said, “If there’s one test of national genius universally accepted, it is success; and if there be one successful country in the universe for the last millennium, that country is England. It is the best of actual nations.”

In World War I, Britain faced a crushing defeat. Eventually, the British Empire was reduced to a Commonwealth. World War II shattered the image of Britain further. Although Britain lost much of its power, it continued to be an influential country. Even after achieving independence, India retained English as an official language. The British parliament system is well established in many Commonwealth countries. Some people still wonder how England still exercises its influence over the minds of men and women.

Staying power

There are many powerful countries in the world today such as the United States, Russia and China. Although England is not a super power, she has staying power. According to Oliver Wendell Holmes, a good part of greatness is simply being there. For that matter, England has been there for many centuries. So far no other country has been able to defeat her. As a result, sometimes we wonder whether we can have a world without England.

England has had an unwritten Constitution for a very long time. Other countries have emulated her political institutions. The British people have an established church with complete religious freedom. Although there are social classes in Britain, there has been no major clash among them. Unlike in many other countries, there are only two leading political parties in England. When the Labour Party is in power, the government is not subservient to labour. Similarly, when the Conservative Party is in power, the government is not conservative.

Most British colonies in the East including India and Ceylon did not sever the cultural and emotional links with Britain and retain them even after achieving independence. India became independent in 1947, but she decided to retain English as an official language. By doing so, India produced a number of English writers such as R.K Narayan. However, Ceylon did not give English any official status and treated it as a link language. As a result, students paid less attention to learning English. They were made to understand that everything can be done by learning Sinhala and Tamil. We have failed to produce English writers in the calibre of J. Vijayatunga who wrote ‘Grass for my feet.’

Politically shrinking

The United Kingdom is politically shrinking. However, its influence vibrates throughout the world. English has brought many nations together. There is a common understanding among countries that share the English language and literature. William Shakespeare’s dramas are staged in countries such as China where English is not an official language. People have come to the conclusion that English has become a broker of ideas and institutions.

England is not an aggressive country. However, if provoked, it can deliver a mortal blow to its enemy. British Prime Minister Margaret Thatcher showed her mettle as the iron lady. Britain held the fort against the might of Napoleon Bonaparte who ruled France. The country can still boast of a heavy moral credit. The British stick to their international agreements. The power of England draws mainly from its language. British people say ‘It’s right’ when it is right’. When it is not right, they say, ‘It’s not right.’ Meanwhile English occupies a pre-eminent place in world languages. All the research work in many parts of the world is available in English. You can learn any subject easily through English.

Apart from the language, people respect British standards which are technical specifications and quality benchmarks developed by the British Standards Institution. The United Kingdom’s independent national standards body was established in 1901. It maintains over 37,000 standards covering industries such as construction, manufacturing and technology ensuring safety and reliability.

British English

Standard British English is the variety of English that has undergone codification to the point of being socially perceived as the standard language associated with formal schooling, language assessment and official print publications. For historical reasons dating back to the rise of London in the ninth century, the form of language spoken in London and the East Midlands became the Standard English used in schools, universities, literature and law.

British English functions as one of the two major foundational and standard varieties of the English language alongside American English. It serves as a primary reference point for spelling and grammar. It acts as a global standard, and international institutions are often defined by specific pronunciation.

Most Sri Lankan doctors primarily move to England for postgraduate training, higher specialisation and better career prospects. They are driven by superior training infrastructure, world-class facilities and globally recognised qualifications.

To sum up, when you think of learning an international language, there is no alternative to English. If you wish to read literature, you cannot ignore eminent English dramatists and poets such as William Shakespeare and John Milton. Many leading Sri Lankans like S.W.R.D. Bandaranaike were Oxford University products. Therefore, English deserves to be made an official language in Sri Lanka.

karunaratners@gmail.com

By R.S. Karunaratne

Opinion

State Literary Awards only for the rich?

Published

17 hours ago

2026/02/16

Thilina Walpola

The Department of Cultural Affairs has once again called authors, and publishers to lodge their entries for selection of the prestigious State Literary Awards 2026.The criteria and conditions required and notified in the public domain, makes it mandatory for the literary work to be printed and published prior to submission for consideration of the awards. There is absolutely no provision for writers to submit their work in Manuscript form.

Where does that leave the financially impoverished writers who are talented, creative and wish to submit a well edited typescript of their work as manuscript for consideration of the State Literary Awards? In a literary environment that encourages a proliferation of self-published books of all forms and features presented by vanity publishers who have their eye on the purse of the author than on literary merit and artistic excellence, it is easy to show that you are an ” established writer” by spending your cash abundantly towards glossy covered books which the printing industry and fawning publishers will lap up with greed.

Even the Gratiaen Prize in Sri Lanka, sponsored by world-renowned Michael Ondaatje allows for Manuscript entries together with published books. Significantly, the manuscript entries that win the prize are assisted to publish their work which is part of the winnings. Many a young, aspiring writer with little funds who won the Gratiaen Prize on merit, but had submitted their entry in manuscript form have been thereby encouraged to submit their work on merit basis only.

It is a fact that the Commonwealth Short Story Prize, a massive state-supported initiative across 56 nations accepts only unpublished short fiction. Further, several countries in the world have established national or state level literary prizes that specifically accept unpublished manuscripts to provide equity in discovering new talent and supporting national literature without bias or favour. In Australia, Jamaica, Philippines, major national awards organised by the State for literature, specifically accept unpublished manuscripts for consideration.

Let’s face the truth. The printing costs are escalating. There is little demand in Sri Lanka for literary work in the English Language in particular. Traditional Publishing where the literary work is reviewed and assessed for talent and creativity and thereafter published is seldom found. The reviews and critical analysis of literary works are rare. But publishers make a pile by pandering to the vanity of aspiring writers who have the financial clout to pay their way through to being featured in prestigious award ceremonies and accolades. Thereafter, their substandard works get a further fillip by bearing the label of “Won the State Literary Award for Literature”! It is a cycle of literary charlatans and their pimps in the publishing industry for whom the price that is paid for publishing and not Meritocracy is the sine-qua-non.

Is this the level playing field promised by the NPP Government and their Marxist protagonists? A government that was voted into power on the platform of affording fair opportunity and equality seems to discriminate in favour of the Haves against the Have- nots in the cultural department to say the least! Anil Fernando

Opinion

Delivering on English

Published

17 hours ago

2026/02/16

Thilina Walpola

English literature offers a rich heritage of wonderful ideas and thoughts. The reader can be intellectually uplifted. It brings refreshing new vistas and stimulating new ideas. However, this English literature has to be first introduced to the student in order to fire up his or her interest and be made aware of this rich source of culture. Students of basic English as a second language work hard and learn all the hum-drum mechanics of the language, for which they get tested and graded. But importantly, nae crucially, this should be followed up with intellectual rewards for the students’ efforts – which, of course, is the enjoyment of the works of literature of the many great writers in the English language. This is the great payoff, the great dividend for all their efforts but this, apparently goes missing.

One of the obvious reasons for the lack of “follow through” may be lack of time allocated in the curriculum – or, perhaps, more darkly, the teachers’ own lack of knowledge of the great range of good reading materials produced by the countless generations of literary geniuses who have gone before. Such writers have laid down for us a heritage of glorious literary works in books and essays, all of which are to be found in any good library. It is thought that much of this good literature ought to be introduced to all students of English, “full stop,” as part of developing a knowledgeable and cultured society. (Isn’t that what we want?) Reading English literature should bring an intellectual enrichment to all those willing to drink from this Bacchanalian horn of plenty.

It must be said finally, that it can be fairly expected that most young people, especially those learning English as a second language, are totally unaware of the many outstanding pieces of writing that propel English to stand tall amongst the rest. That is, students need to be first introduced to great writings and have a spark of interest ignited in these great works of literature.

For example, by being introduced to “Daffodils,” a short descriptive poem by William Wordsworth, the student can get some very pleasant ideas to think on.

Do not overlook Conan Doyle’s “Sherlock Holmes” detective stories, each one captivating the reader’s attention right to the end. It is by these short stories that the novice reader can first consolidate his power of reading.

For light reading Jerome K. Jerome’s book “Three Men in a Boat” is suggested. On one occasion he goes to the library suffering from a slight hay-fever (allergy) seeking a cure. He consults a book, “Lexicon of Pharmacology”, and recoils in horror as his symptoms fit most of those diseases described in the book! He concludes he cannot live much longer and staggers home to rest and recuperate! This is a well related tale in the book – although seemingly quite implausible!

Similarly, by having the poem meanings explained, e.g. “What is Life if Full of Care?” by William Henry Davis – how he regrets that we humans are always in a hurry, too busy to notice or see the delights of nature, and scenes of natural beauty, e.g., a young woman’s smile as she passes by; we have no time to make friends and even kiss her. Regrets! Explaining this to students would bring a certain intellectual insight.

John Keats’s poem, “Ode to Autumn” is another great work describing the ripening fruits of the autumn season and how nature as a living being, brings to fruition all the good things of a rural landscape quietly humming with warmth after a hot summer.

Again, it is likely necessary to explain to a young, Sri Lankan mind the meaning of the descriptive poetry found in this magnificent poem.

This is the real English to be tasted and then swigged at lustily in pleasure and satisfaction, not some writing airing historical grievances for children to study!

1970 British Cohort Study

It should be observed here that the ‘1970 British Cohort Study’ followed 70,000 people to examine various aspects of their lives. One result discovered was that if a young person reads a lot, it develops his/ her general intelligence no-matter his parents; it makes him smarter.

It was also noted that reading brings life-long benefits; it improves mood, it helps with social skills, increases empathy, reduces anxiety, protects against depression and slows brain decay, the study found.

But these days many young people never gain a great competence in reading English; the fear is that standards are falling. This is bringing poorer critical thinking, less depth of personality and less empathy for others which has the result of a more turbulent society.

People are urged to switch off their headphones and read more of what they like – try reading the newspapers!

Priyantha Hettige