Many or most people in Israel and Scotland have received COVID-19 vaccinations, and reports from both confirm that vaccines largely prevent people from getting sick. But there is another question: do they also block infection?
Many say the experts say the answer.
If vaccines are rolled out worldwide, not only repelling the symptoms but also repelling the virus itself, it could sharply slow down the spread of the pathogen and accelerate the return to normal.
“If the real impact on infections was very large, it would be good news, because that’s what we need for herd immunity,” said Marc Lipsitch, director of the Center for Communicable Disease Dynamics at the Harvard TH Chan School of Public Health. , told AFP. .
Herd immunity is achieved when most of the population – estimates range between 60 and 80 percent – have acquired defense against a virus, either through vaccination or because humans caught the bug and survived.
But if the vaccines Pfizer, Moderna and AstraZeneca – and perhaps others manufactured in China, Russia and India – do a bad job of protecting people from infection, even people who have been injected remain potential, unconscious carriers.
“The biggest concern is that the vaccines prevent disease, hospitalization and death, but that they will not adequately prevent transmission,” said Peter English, a UK-based communicable disease control consultant and former chairman of the UK Medical Association association’s medical committee for public health said. AFP.
In that scenario, communities and economies already degenerating through the pandemic will face prolonged masking, social distance and more or less harsh closures until the vaccination of campaigns can be completed.
“There is also a greater risk that ‘escape variants’ of vaccines could be thrown up if the virus continues to circulate,” English said.
Several such variants – more contagious, deadly or both – have multiplied in England, South Africa and Brazil, as the SARS-CoV-2 virus is more difficult to find new hosts, a predictable phase in the evolution of a pandemic .
But recent studies and other prospects suggest reason for optimism.
Research covering the entire Scottish population of 5.4 million – with a fifth vaccinated with the Pfizer or Oxford / AstraZeneca jabs – provides a real validation that the vaccines more than 90 percent of the time COVID symptoms and disease prevent.
A study published Wednesday in the New England Journal of Medicine – which compared two groups in Israel of nearly 600,000 people each, one vaccinated and the other not – also reported that the disease is less in line with clinical trials .
But in contrast to the study from Scotland, the Israeli findings also showed that infections in the vaccinated group decreased sharply – with 92 per cent among those who were at least one week after the second of two doses.
The actual level of protection may not be so high because Israel does not systematically test for COVID among people without symptoms, the authors acknowledge.
“They are unlikely to detect asymptomatic cases, and we know that people without symptoms can still transmit the infection,” Engels said.
But the results are still encouraging, he added.
“These findings give us hope that the vaccine alone can get the R-number below 1,” English said, referring to the threshold within which a virus continues to spread.
“If it can – and this is the big question – we will ultimately no longer have to take behavioral measures such as locking up or masks to interrupt the spread.”
But how is it that despite hundreds of studies, as well as rigorous clinical trials involving tens of thousands of people, resulting in more than half a dozen successful vaccines, we do not know how well they block infection?
Lipsitch said one reason is that when the pandemic began its devastating march around the world last year, it was not a priority.
“What the world community has paid the most attention to is the question they wanted to answer quickly, how well vaccine diseases work,” he said, noting that clinical trials were designed with that in mind.
“We got answers quickly,” he added. “But we would not do that if we tried to do too many things at once – especially things like measuring the impact on infection.”
Another reason is the challenge of detecting millions of diseases ranging from zero symptoms to death.
“It’s hard to try to figure out how many people are asymptomatic but potentially contagious,” Engels said. “How do you identify them unless you test them all regularly?”
In addition, even the best degree of infection – so-called PCR tests – is only about 70 percent sensitive outside of laboratory conditions, he added.
But the extent to which vaccines are affecting the infection is likely to come into focus soon.
“The limited available data suggest that vaccines will at least partially reduce transmission, and studies to determine this with greater clarity are ongoing,” said Angela Rasmussen, a virologist at the Center for Global Health Science and Security. written at Georgetown University Medical Center, Wednesday. in The New York Times.
One of the most promising indications so far comes from the clinical trials for the Moderna vaccine developed in the United States.
“When people came in for their second shot, they were tested for viruses in the nose,” says Lipsitch, who is writing a study that interprets the data.
“There was a 60 percent reduction in the proportion who had virus on Day 28 when they received the vaccine, rather than a placebo, on Day Zero.”
The effect was even greater, he added.