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The green light from the health authorities is approaching, the doses are in production and governments, laboratories and experts promise transparency on the safety of future COVID-19 vaccines, developed so quickly that they raise concerns about their safety.
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One statistic will be central to their persuasive endeavor: Historically, nearly all of the negative effects of vaccines appear within six weeks of vaccination.
However, participants in Pfizer / BioNTech and Moderna’s large clinical trials, whose vaccines are in a better position to be authorized in December in the US and Europe, were followed up for two months at the request of the US agency. medications (FDA).
“There’s a difference between fast and too fast,” Saad Omer, director of the Institute for Global Health at Yale University, told AFP. Two months will be enough to detect “the vast majority” of side effects.
Usually, the FDA requires six months of follow-up. But if nothing bad happens in two months, another four months are unlikely to reveal anything else. The health emergency transforms the risk / benefit calculation.
“At this point in the pandemic, we may not need the perfect data, even if I do,” Grace Lee of Stanford, a member of the Centers for Vaccine Advisory Committee, told AFP. diseases (CDC).
“How long do we have to wait to get slightly better information,” he asks, “letting the pandemic continue?”
Above all, the trials have a very reassuring advantage, their size: 44,000 participants for Pfizer, 30,000 for Moderna.
Half of the volunteers were followed in this phase for at least two months. The FDA will then have safety data on tens of thousands of vaccinated people. This is well above the 6,700-person average for vaccines authorized over the past decade.
Pfizer and Moderna reported that within two months of the second dose, there were no “serious” side effects that were life threatening or resulted in hospitalization or disability. This category includes dangerous allergic reactions (anaphylactic shock) or neurological problems.
What have we observed? Tiredness, headache, muscle aches, joint pains, redness and bite pains, especially after the second dose. Level 3 effects, in medical jargon, resolved without hospitalization.
However, the FDA will review all safety data, not just the summaries provided by manufacturers in their publications.
Experts are also reassured by the apparent absence, in all studies, of a disease-facilitating effect from vaccines, as was observed with a respiratory syncytial virus vaccine in the 1960s.
Once authorized, surveillance, or pharmacovigilance, will last for years: in the United States and Europe there are established systems to statistically detect any increase in certain serious medical events in the vaccinated population and to confirm a possible cause and effect link.
For flu shots, the CDC, for example, found a possible, tiny increase in the number of cases of Guillain-Barré syndrome (where the immune system attacks the nervous system), but with no real certainty.
More importantly, “they all happened within six weeks,” insists Edward Belongia, a researcher at the Marshfield Clinic Research Institute, who has been evaluating flu vaccines for more than 15 years for the CDC.
It was this post-authorization surveillance that led to the withdrawal of the first rotavirus vaccine in the United States in 1999, nine months after its authorization. Rare cases of intestinal obstruction have been observed in young children vaccinated for two weeks.
In general, monitoring leads instead to using restrictions on certain groups, says Saad Omer.
Faced with these reduced risks, some countries are less suspicious than others. In China, 88% of people surveyed by Nature in June were ready to be vaccinated, compared to 59% in France and 55% in Russia.
In the United States this summer, fear of Donald Trump’s pressure had caused a wave of hesitation. But the elections passed and an Ipsos poll in November found a turnaround in favor of vaccines.
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