Confusing vaccine efficacy-what does it mean to a lay person?-Dr. Harold Gunatillake

Harold Gunatillake

“The vaccine trials with so many people dying with the Coronavirus, have been nothing short of a miracle.”
There is some confusion in the interpretation of a vaccine when it is said the efficacy is 95%. That does not imply that 5% of the vaccinated people can get the infection.
Vaccine efficacy is the percentage reduction in a disease in a group of people who received a vaccination in a clinical trial.
Putting it another way the scientists can calculate how well a vaccine candidate works by looking at the difference in new cases of the disease between the group receiving a placebo and the group receiving the experimental vaccine. This is called vaccine efficacy.

What this percentage means is that 95% of the people who entered the trial had a 95% lower risk of getting the COVID-19 compared with the controlled trial that was given the placebo. In other words, the people who were vaccinated with the Pfizer vaccine has a 20 times less likely chance of getting the virus.
A 2020 study on the Pfizer vaccine of more than 43,000 participants published in The New England Journal of Medicine (NEJM), found the vaccine was 95 percent effective at preventing Covid-19.
So, what 95% efficacy means is that the chances of preventing the disease is 95%, large studies have shown.
This is not the same as vaccine effectiveness, which measures how well a vaccine works when given to people in the community outside the clinical trials.
You may have read that the efficacy rate of Pfizer vaccine is 95%, Moderna’s vaccine 94% and the Johnson & Johnson’s is only 66%.

In its first 3 weeks administered in the US, Moderna’s COVID vaccine had 10 confirmed severe allergic reactions out of 4 million doses, with the Pfizer rate slightly higher.
Additionally, Professor Godfrey, Doherty Institute, says AstraZeneca may prove to be more effective than currently thought, given that initial data from two different doses ranged between 62% and 90%.
However, Professor Dale Godfrey, Immunology Theme Leader at the Doherty Institute, told news even though the arguments for higher efficacy hold some validity and Pfizer and Moderna’s data are impressive, that it in no way discredits AstraZeneca’s candidate.
‘It is important to remember that the AstraZeneca vaccine is at the right end of the efficacy spectrum,’ he said. ‘Regulators were saying 50% or greater is what’s required for a vaccine to be worth distributing.’
According to the WHO, the AstraZeneca-Oxford vaccine is a viral vectored vaccine called ChAdOx1-S has been found to have 63.09 per cent efficacy and is suitable for low-and middle-income countries due to easy storage requirements. In real terms the number of people who contracted the disease after the vaccination trial is about 0.04% and has no connection to the efficacy of a vaccine, which is meaningless from the people’s point of view. That signifies the importance of having the vaccine, and your chances of contacting the disease is so remote as 0.04%.
From our point of view that is more important than talking about the efficacy of a specific vaccine. Efficacy is important for the researchers who run the trials, for their comparative studies, and not for those who receive the vaccines.
On the other hand, it is important to know about the efficacy of a vaccine, because if the efficacy is below a certain level, it’s not possible to achieve herd immunity.
The term herd immunity comes from the observation of how a herd of buffalo forms a circle, with the strong on the outside protecting the weaker and more vulnerable on the inside.
Those who are strong enough to get vaccinated directly protect themselves from infection. They also indirectly shield vulnerable people who cannot be vaccinated.
It is estimated that 60%-70% of people would need to be immunised against COVID19 to achieve herd immunity – the point at which its transmission begins to drop dramatically.
Herd immunity is the end game for the pandemic, but the AstraZeneca vaccine won’t get us there.
What is important for the receivers of the vaccine to think whether they should have the vaccine, and after getting it how they behave, and how long will the antibodies formed last in your body to fight an infection, and what complications could arise, especially among those old people who have other chronic disabling issues.
Based on what we know about vaccines for other diseases and early data from clinical trials, experts believe that getting a COVID-19 vaccine may also help keep you from getting seriously ill even if you do get COVID-19.
Getting vaccinated yourself may also protect people around you, particularly people at increased risk for severe illness from COVID-19.
Men can lower the sperm count after COVID-19 infection.The study researchers, from the University of Florence in Italy, analysed semen samples from 43 men ages 30 to 65 about one month after they had recovered from
COVID-19. They found that 25% of the men had low sperm count, and nearly 20% had azoospermia, or the total absence of sperm in semen. Four cases of this variant were detected in Sri Lanka, recently. China has allegedly pushed the Sri Lankan government to approve Covid-19 vaccines manufactured by Chinese state-owned firm Sinopharm.Sinopharm vaccine candidates haven’t formally been proved safe or effective, but thousands of people have been injected with them in China. Those users could be taking big risks. People who have taken ineffective vaccines might believe they are safe and engage in risky behavior. They can be barred from taking another, better vaccine because they have already been injected. In a few cases in the past, unproven vaccines have caused health risks.
India has contributed 500,000 doses of the locally manufactured Covishield jab. Covishield -is the local name for the Oxford AstraZeneca vaccine developed in the UK and Covaxin, locally made by pharma company Bharat Bioitech.
Covax is formed from the inactivated vaccine which means that is made up of killed coronaviruses, making it safe to be injected into the body.
Covax has not been approved for use, but Bharat Biotech has defended the approval, saying Indian clinical trial laws allowed ‘accelerated’ authorization for the use of drugs after the second phase of trials The Oxford-AstraZeneca vaccine is being manufactured locally by the Serum Institute of India.
It is made from a weakened version of a common cold virus known as adenovirus from chimpanzees. It has been modified to look more like coronavirus- although it can’t cause the illness.
It is 62-90% effective.
In conclusion, With more challenges yet to come, let us discuss how safe any vaccine is for all of us. Safety has been compromised. All trials have been through the correct ’phrases’ or process of any normal drug or vaccine. To date, there has not been a single associated death related to COVID vaccines and only a handful of potentially
serious events.
At this time, three vaccines have already broken cover and demonstrated efficacy higher than we had ever hoped. The bar was set by regulators at around 50%. Both Moderna and Pfizer reported 95% efficacy, and Oxford University reported 90% efficacy for a particular dosage regimen. Safety data is still to follow, but the track record of vaccines is excellent, and we all should be proud of a confident future.
However, the increasing momentum of the antivaxxers and conspiracy theorists propaganda through the social media is worrying.
The global death toll from COVID-19 is just under 2.4 million. The number of confirmed cases is above 108 million and more than 61 million people have recovered, according to the Johns Hopkins University tally at 7.30pm.
The World Health Organization(WHO) granted two versions of the AstraZenecaOxford COVID-19 vaccine for emergency use produced by AstraZenecaSKBio(Republic of Korea) and the Serum Institute of India(SII).
The Johnson & Johnson vaccine had 66% efficacy at reducing severe and moderate cases of COVID-19, which include either two mild symptoms or one more serious symptom, such as low blood oxygen levels or increased respiratory rate, Live Science previously reported. In other words, people vaccinated with the J&J shot were three times less likely to get a mild or moderate case of COVID-19 compared with participants who received a placebo. Meanwhile, the Pfizer/BioNTech vaccine had 95% efficacy, and the Moderna vaccine had 94% efficacy at preventing symptomatic COVID-19, meaning any positive test with even one symptom, however mild. All three vaccines are thought to be 100% effective at preventing hospitalization and death related to COVID-19.
Israeli researchers have found that having just one shot of the Pfizer coronavirus vaccine may lead to lower viral loads, making it harder to transmit COVID-19 if someone becomes infected after the first dose.
A separate independent Israeli study, from the country’s largest healthcare provider Clalit, found a 94 per cent drop in symptomatic COVID-19 infections among 600,000 people who received two doses of the Pfizer vaccine.
• Scientists are hopeful that T cells could maintain lasting immunity against COVID-19 variants. Some coronavirus-vaccine developers are already looking at ways to develop next-generation vaccines that stimulate T cells more effectively.
Hope this talk was useful.
Goodbye for now.


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