Here’s how to determine the effectiveness of COVID-19 vaccines

Paris: The race to develop a vaccine against Covid-19 also includes significant numbers, difficult to explain to the general public and related to the level of effectiveness, which ranged between 95% and 70% with one of the vaccines, paradoxically, a better answer. using a lower dose.

Among the volunteers in each trial, some are given the vaccine and others a placebo, so that researchers can compare the two groups.

Volunteers continue their lives as usual during the experiment. Over time, some of them will naturally contract the SARS-Cove-2 virus. If the vaccine were effective, there would be fewer patients among the vaccinated participants than those who received the placebo.

In theory, the vaccine would be 100% effective if no patient who participated in the trial belonged to the group of vaccinated volunteers.

The results recently announced by several of the competing research teams refer to the latest phase of their clinical trial, Phase 3, for which it attracted tens of thousands of volunteers.

These results were revealed once a predetermined number of Covid patients among the volunteers was reached: 95 patients for the American Modern laboratory on November 16, 170 for the American Pfizer and the German Biontech on November 18 and 131 for the European AstraZeneca and Oxford University, Monday.

Pfizer and Biontech reported 95% efficacy: of the 170 patients, 8 were from the vaccine group and 162 from the placebo group. Moderna had a close result of 94.5% (5 patients in the vaccinated group, 90 in the placebo group).

Pfizer measured the effectiveness of its vaccine one week after the second and last injection and our moderine two weeks later.

AstraZeneca / Oxford: average efficiency of 70%

For their part, AstraZeneca and the University of Oxford announced on Monday an average efficacy of 70%, calculated from the results of two different protocols.

The effectiveness was 90% for the volunteers who received half a dose the first time, then a full dose one month later. It dropped to 62 percent for another group who received two full doses, one month apart. The results were a paradox, which according to experts was only an apparent contradiction.

‘We all expected that two full doses would lead to the best response,’ said one of the lead researchers, Andrew Pollard, at a news conference.

This could be due to a smaller starting dose that “better mimics what happens during a real injury,” according to her colleague Sarah Gilbert.

Another hypothesis is that this could also stem from the technology used in this vaccine. Indeed, AstraZeneca and the University of Oxford have relied on a “viral vector” technique, in which another virus (here, a chimpanzee adenovirus) is used that is modified to transmit genetic material to our cells that can fight Covid-19.

Several experts who have commented on these findings have stated that a very strong first dose of a vaccine could actually cause the immune system to fight the virus used as a vector, contrary to the desired effect. This point needs to be clarified in subsequent experiments.

Finally, on November 11, Russians from the Gamalia Institute confirmed that their vaccine was 92% effective. But they were based on very few patients (only 20).

It is impossible to know at the moment, especially since all these results have not been announced except in press releases, without publishing them in detail in a scientific journal.

However, although its efficacy numbers appear to be lower than others, experts believe the AstraZeneca / Oxford vaccine could have an added benefit.

The British Science Media Center quoted University of Edinburgh Professor Eleanor Riley as saying that “unlike other experiments, the Oxford / AstraZeneca team examined all participants weekly for asymptomatic lesions.”

Indeed, one of the main questions is whether these vaccines prevent transmission of the virus as well as reduce the severity of the disease in those who received them.

The University of Oxford said in a statement: “We have the first indications that this vaccine may reduce the transmission of the virus, as a decrease in asymptomatic infections has been observed.”

But all these data are still preliminary. Another expert, Dr Julian Tang of the University of Leicester, as quoted by the Media Science Center, warned that “the differences in efficacy are based on an analysis of 100-200 patients out of a total of 30,000-50,000 volunteers for each. vaccine, and therefore these numbers could see huge differences after that. ” “.

Not knowing the duration of protection provided by vaccines

Many other questions remain unanswered. First, we don’t know how long these vaccines provide protection.

Second, it is not known whether its effectiveness is identical in populations most at risk, starting with the elderly. This group is more susceptible to severe Covid-19, so the vaccine needs to be effective in this population group.

Pfizer and Biontech have confirmed that their vaccine efficacy exceeded 94% for those over 65. However, as the results have not been published in a scientific journal, the details are not yet known.

On 19 November AstraZeneca and the University of Oxford published the results in the prestigious medical journal The Lancet, which showed that their vaccination induces an immune response similar to that of young people (ages 18 to 55).

However, these published results are not related to the third phase but to the previous or second phase in which the total number of volunteers was much lower (560 versus 23 thousand) and is a non-representative sample of the general population.