As the global coronavirus death toll approaches 2 million, a growing number of countries are rolling out the first generation of new coronaviruses.
According to World health Organization guidelines, vaccine manufacturers must meet a 50% vaccine efficacy target, a threshold that many leading Western vaccine candidates have long since crossed.
The majority of Australians will receive the Oxford-AstraZeneca vaccine, which in recent days has sparked important discussions in Australia about whether the vaccine is sufficient to achieve herd immunity.
However, there is no vaccine that can definitively guarantee that herd immunity can be achieved.
So far, regulatory-approved vaccines have only been able to reduce the severity of the new crown disease; it is not known whether they will prevent those who receive the vaccine from contracting the virus, or from spreading it to others, or how long that protection will last.
Despite these unknowns, hundreds of millions of doses of different types of vaccines with varying efficacy have been ordered worldwide.
Although a 50 percent efficacy target may seem low at first glance, experts believe it is sufficient to make a difference in a global health emergency.
So why is such a target set? What do we need to know when we talk about vaccine efficacy?
What do vaccine efficacy and effectiveness mean?
Although they sound similar in English, efficacy and effectiveness are actually quite different. (AP: Mark Lennihan)
First, it is important to understand the difference between vaccine efficacy and effectiveness.
Adrian Esterman, professor of biostatistics and epidemiology at the University of South Australia, told the Australian Broadcasting Corporation (ABC) that the difference is simple.
“Efficacy is how well a vaccine works in clinical trials. Effectiveness explores: ‘How effective is it in real populations?'” Dr. Esterman said.
In other words, if 100 people are vaccinated in a clinical trial, then 50 percent efficacy means 50 percent of those vaccinated will be immune to the disease.
But that efficacy figure could fluctuate if the same vaccine is widely distributed in the community, Dr. Esterman said, because the trial may not have taken into account every variable of the demographics.
For example, the effectiveness of the flu vaccine fluctuates between 40 and 60 percent each year, according to the U.S. Centers for Disease Control (CDC).
“In trials, it’s common to be very selective about the volunteers who are allowed to participate,” says Dr. Esterman.
“For example, you may not want patients with advanced cancer or pregnant women.
“But in the real world, people get pregnant and there are really a lot of different situations, especially in older people with chronic illnesses.”
To measure effectiveness, vaccine manufacturers conduct phase IV trials to monitor for adverse reactions or any other type of unforeseen problems.
Why does WHO require a minimum vaccine efficacy of 50%?
The average efficacy of the Oxford-AstraZeneca New Crown Pneumonia vaccine was 70.4 percent.
WHO outlines the minimum standards it has set for the New Crown vaccine in a document called the Target Product Profile (TPP).
The TPP includes indicators of efficacy, duration of protection, dosing regimen and storage conditions.
The document says the WHO prefers an efficacy of 70 percent, but a minimum of 50 percent.
Jodie McVernon, director of epidemiology and infectious diseases at the Melbourne-based Doherty Institute for Infection and Immunology, said that while vaccine developers should aim for the highest possible efficacy, the world is in a “very unique situation.
She said the WHO’s 50 percent minimum standard “actually reflects the health emergency we’re facing” and that regulators around the world are looking for anything that might help.
“We are now facing a health emergency with overloaded health systems, catastrophic economic and social consequences, and many, many deaths,” Dr. McVernon said.
“Our goal is to contain the outbreak as best we can, especially in areas where it is raging, and then continue to develop an understanding of vaccines.”
Vaccine regulators in the U.K., U.S., Canada, Australia and the European Union have also recommended a minimum target of 50 percent.
What is the current efficacy of each vaccine?
There are no independently validated efficacy results for the new Chinese crown candidate vaccine.
What we do know is that approved Western vaccines report efficacy well above 50%, with Pfizer at 95%, Modena at 94.5%, and Oxford-AstraZeneca averaging 70.4% (there are two different efficacy values for different doses of this vaccine).
Australia has received 10 million doses of Pfizer vaccine and 53.8 million doses of AstraZeneca vaccine.
While Russian and Chinese vaccine candidates have been approved for use in a number of countries, neither country has submitted Phase III trial data for international peer review, as has been done for Western vaccine candidates.
In early November last year, the developers of the Russian Satellite V vaccine announced 92% efficacy of their candidate based on an interim analysis of 20 cases of neo-crown among 16,000 volunteers in the Phase III trial.
Meanwhile, China’s neo-crown vaccine candidates have been accepted by several countries around the world that have analyzed these vaccines and come up with different efficacy figures.
China National Pharmaceutical Corporation (Sinopharm) has a vaccine with 79.34% efficacy. However, the United Arab Emirates released data last month that said this vaccine had an efficacy of 86%.
Another Chinese vaccine candidate, produced by China’s Kexing Bio, has an overall efficacy of 50.4% according to Brazilian officials.
Indonesia and Turkey recorded higher efficacy figures in trials of the Coxin vaccine, but these clinical trials were considered too small to produce substantial data.
Prior to the release of the vaccine efficacy data, Anthony Fauci, director of the National Institute of Health and Infectious Diseases, told attendees at a Brown University forum last August that it may be unrealistic to expect the new crown vaccine to achieve high efficacy.
“I believe we’re going to get an effective vaccine. But we don’t know if it’s 50 percent or 60 percent,” Dr. Fauci said.
“I would like to see 75 percent or higher, but 98 percent effectiveness is not very likely.”
Now, two leading genetic vaccines are 90 percent effective, which Dr. McVernon said “exceeds expectations” and is “remarkable.”
These vaccines use new technology to produce in the body the SARS-CoV-2 protein that the vaccines are designed to prevent, and it is this protein that causes the new crown infection.
For the vaccine to work, the body interprets this protein as a foreign substance and triggers an immune response that produces antibodies to fight this virus and remember it the next time. Dr. McVernon said the urgency of the outbreak has had an impact on expectations of vaccine efficacy. “That’s certainly what the vaccine is expected to achieve,” Dr. McVernon said, “but even if it’s only 50 percent, it will make a significant difference in a health emergency.”
Is it difficult to get the vaccine across the 50 percent mark?
The social and economic impact of the COVID-19 pandemic prompted the vaccine to be introduced in record time.
Both Dr. McVernon and Dr. Esterman emphasized that it was time to define the parameters of vaccine effectiveness.
During non-pandemic times, Dr. McVernon said, vaccine approval for non-emergency diseases is a “long and complex” process that typically takes “20 to 30 years” from conception to manufacture.
She said regulators must consider many factors, including how common the disease is, the costs associated with treating it, and the efficacy, costs and side effects of the vaccine.
Given that the world is in a state of health emergency, Dr. McVernon said regulators must balance efficacy expectations with the real and current threat posed to the global population by the new coronavirus.
“Sometimes getting the highest possible efficacy is not as important as vaccinating as many people as possible,” she said.
“If the only vaccine candidate ranked No. 1 had 50 percent efficacy and did something, you would want to get the population vaccinated with it and continue to develop a better vaccine.
“As it becomes less of a global epidemic and more of an endemic around the world, then the bar for having better and better vaccines will be raised.
“We’re not saying goodbye to this virus any time soon.”
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