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ZURICH: There has been a flurry of good news this week from the developers of the COVID-19 vaccine, with Pfizer and BioNTech announcing the first data indicating that their mRNA candidate is more than 90 percent effective.
A Russian project came out a day later, touting a 92 percent efficiency for candidate Sputnik V, named for the Soviet-era satellite, based on a smaller data set.
HOW DO MANUFACTURERS REACH EFFICIENCY NUMBERS?
In Pfizer’s case, it waited until 94 volunteers in its late-stage clinical trial of more than 43,500 people (half received the vaccine, the other half received a placebo) tested positive after developing symptoms.
For an efficacy greater than 90 percent, no more than eight people among those who tested positive had received the vaccine, and the rest had received the placebo.
“Generally speaking, there are likely eight to 86 cases in the treated and placebo groups,” David Spiegelhalter, a Cambridge risk professor and statistician, told Reuters.
“It doesn’t take a lot of sophisticated statistical analysis to show that this is profoundly impressive. It just hits you between the eyes.”
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In Russia, the Gamaleya Institute, developer of Sputnik V, reached its preliminary efficacy figure of 92 percent based on 20 illnesses in 16,000 volunteers as its late-stage trial progresses. It aims to reach 40,000 people.
Of the 16,000 people, about a quarter received the placebo.
“It suggests that there is some effect, but it is insufficient to estimate its magnitude,” Spiegelhalter said.
HOW MANY PEOPLE SHOULD GET SICK ON LARGE VACCINE TESTS?
Some experts say that ideally 150 to 160 people in a trial of tens of thousands of participants must become ill before making a reliable evaluation of the efficacy of a vaccine. However, it is an empirical rule open to interpretation.
“There is no such regulatory standard that requires X number of events to make a reliable decision,” said the government-funded Swiss Organization for Clinical Trials. “The number of (infections) has to be seen in relation to the disease and its risk profile. It’s more of a case-by-case assessment.”
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Regulators generally strive to be at least 95 percent certain that the test reading is not the result of random variations that have nothing to do with the compound tested.
For test sponsors, there is safety in the numbers, as a large enough test can guarantee that the 95% reliability hurdle is overcome. But the greater the underlying clinical benefit, the fewer trial participants it took to create that clarity.
In the Pfizer and BioNTech trial, they planned a final analysis when 164 people became ill, with multiple interim tests pre-planned along the way.
They skipped an analysis of 32 patients, and once they were ready to take a look at the 62-person mark, 94 fell ill.
Details of the Russian trial are unclear, without access to its protocol.
HOW DO THESE RESULTS COMPARE WITH OTHER DRUGS OR VACCINES FOR OTHER DISEASES?
In normal drug trials, for illnesses like terminal cancer, the benefits of new drugs may be less obvious, with survival benefits of just a few months, sometimes revolutionary for patients on the brink of death.
However, for vaccines, marginal protection is inadequate, and the World Health Organization ideally wants to see at least 70% efficacy in trials, while the US Food and Drug Administration wants at least the fifty%.
The 90 percent efficacy reported in the Pfizer and Russia trials surpasses those, and appears to exceed that of typical flu vaccines, which are estimated by the US Centers for Disease Control and Prevention (CDC). They reduce the risk of disease by 40 to 60 percent.
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For other injections, the CDC estimates the effectiveness of a two-shot measles vaccine at 97 percent and a two-dose chickenpox vaccine at 90 percent. Two doses of the polio vaccine are 90% effective, reaching almost 100% with a third.
CAN WE EXPECT THE EFFICIENCY RATES TO BE MAINTAINED AS THE TESTS ADVANCE?
Pfizer acknowledged Monday (November 9) that its final percentage of vaccine efficacy may vary. Still, Spiegelhalter said the study design seems likely to stick overall, based on the 94 sick participants.
“In this case, the effect is so big, even if there is a little pullback, if the effects get a little bit smaller over time, it is very unlikely to be significant,” he said.
WHAT ABOUT EFFECTIVENESS IN THE REAL WORLD, MUST VACCINES BE APPROVED?
The interim data is promising, as it appears to show that a vaccine may be effective in preventing COVID-19.
The jump to mass vaccines, however, presents new hurdles, in particular for an mRNA vaccine like Pfizer and BioNTech, which must be stored and shipped at minus 70 degrees Celsius.
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Additionally, the Pfizer-BioNTech vaccine requires two doses, ideally 21 days apart. If people don’t meet the schedule, it can affect how well the vaccine works.
Protection against mumps, for example, drops from nearly 90 percent to 78 percent if people don’t get a follow-up vaccine.
Swiss epidemiologist Marcel Tanner, president of the Swiss Academies of Arts and Sciences and one of the government’s top COVID-19 scientific advisers, expects possible variations in efficacy among older people, whose immune systems weaken over time, or those with immune disorders.
“Efficacy says, ‘Does it work?’ Efficacy says: “Can it be applied? Can you bring effectiveness to people? “Tanner said.” But there’s no question: 90 percent effectiveness, at that stage, is a pretty good result. “
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