The New Science Challenge: How Vaccines Can Prevent Reduced Transmission of COVID-19

The ability to protect people from COVID, to create antibodies that reduce the impact of the disease is a real situation. Now scientists are trying to find out how well vaccines can prevent transmission reduction. New data from the Centers for Disease Control and Prevention (CDC) reveals that COVID-19 infections still occur in vaccinees, but at an extremely unusual rate.

As of mid-April, the entity had received reports of just over 5,800 fully vaccinated individuals who in the United States had been infected regardless. Almost half of these infections (45%) involved people under the age of 60. Only one of them died.

Specialists have focused on defining the effect of COVID-19 vaccines in terms of disease prevention. There are still tests to see if a fully vaccinated person could also develop an infection, without symptoms, and unknowingly transmit the virus to another person.

The distinction is valuable because many do not perceive that the doses are intended to prevent disease, but not necessarily infection. This means that not all vaccines prevent fully vaccinated people from passing the pathogen to others.

“The main thing in vaccine development is to prevent people from getting infected, but it is extremely difficult to achieve this says Jason Kindrachuk, assistant professor of virology at the University of Manitoba in Winnipeg, Canada

Four months after the Food and Drug Administration cleared the first COVID-19 vaccines, the CDC had enough data to suggest that they significantly reduced infections and therefore the risk of a vaccinated person infecting others. .

According to an article published in the journal Nature, the first preliminary analyzes suggest that certain vaccines seem to have a blocking effect on the transmission of the virus. However, experts believe this data can be misleading as the drop in infected people may also be due to other factors such as lockdowns. However, according to Larry Corey, a vaccinologist at the Fred Hutchinson Cancer Research Center in Seattle, Washington, notes that “a vaccine that is very effective at protecting people from infection in the first place will also help reduce transmission.”

Vaccines are unlikely to significantly slow infections. But, they will cause the already vaccinated and infected person to transmit the virus to a lesser extent or to do so with a lower viral load.

Israel is the country in the world that has the best developed its vaccination program, which is why hundreds of researchers are measuring the viral load of the population, that is, the concentration of viral particles in vaccinated people who are then tested positive for SARS-CoV-2.

In preliminary work, the teams observed a significant decrease in viral load in a small number of people who became infected with the coronavirus between two and four weeks after receiving the first dose of Pfizer vaccine, compared to those whose became ill within the first week or two after vaccination.

However, this observed reduction in viral load is not enough to determine whether someone is less contagious in real life, the researchers say.

To really determine whether vaccines prevent transmission, researchers look for close contacts of those vaccinated to see if they are indirectly protected from infection.

Infection relative to severity

During the trial of Moderna’s vaccine, produced in Boston, The researchers took samples from all of the participants to see if they had viral RNA. They found a two-thirds drop in the number of asymptomatic infections in people who received the first injection of the two-dose vaccine, compared to those who received a placebo. But they only tested people twice, a month apart, so they could have missed the infections.

The UK vaccine trial produced by the University of Oxford and AstraZeneca sampled participants weekly and estimated a 49.3% reduction in asymptomatic infections among a subset of vaccinated participants compared to the group not vaccinated. .

New York-based Pfizer and maker of another leading COVID-19 vaccine, said it will start monitoring participants every two weeks in vaccine trials that have taken place in the United States and Argentina . to see if the injection can prevent infection.

Two others, from the Mayo Clinic and the UK, included more than 85,000 healthcare workers routinely tested and fully immunized with the Pfizer-BioNTech vaccine. The vaccine reduced the infection between 85 and 89%. All of this evidence points to the ability of the three vaccines to prevent infection in the majority of people vaccinated.

Further evidence accumulated in March with a large number of studies of mRNA vaccines. One in 9,109 health workers in Israel found that infections were reduced by 75% after two doses of the Pfize-BioNTech vaccine. Another found that the viral load dropped four times in those who received a dose and then developed an infection.

Among more than 39,000 people screened for infections at the Mayo Clinic, patients had a 72% lower risk of infection 10 days after the first dose of one of the mRNA vaccines and 80% less after both doses . The New England Journal of Medicine published research letters showing reduction in infections among fully vaccinated healthcare workers at the University of Texas Southwestern Medical Center, Hebrew Hadassah University in Jerusalem, and the University of California in Los Angeles and San Diego.

A CDC study in early April of 3,950 healthcare workers who were screened weekly for three months after receiving both doses of either mRNA vaccine found that full vaccination reduced infection ., regardless of symptoms, by 90% and a single dose reduced the infection by 80.

In preliminary work, a team observed a significant drop in viral load in a small number of people infected with SARS-CoV-2 within two to four weeks after receiving their first dose of Pfizer vaccine, compared to those who contracted the virus within the first two weeks after the injection . “The data is certainly intriguing and suggests that vaccination may reduce the infectivity of COVID-19 cases, even if it does not completely prevent infection. “Says Virginia Pitzer, infectious disease modeler at the Yale School of Public Health in New Haven, Connecticut. The Oxford-AstraZeneca trial also observed a greater reduction in viral load in a small group of vaccinated participants than in the unvaccinated group. But it’s not yet clear whether these observed reductions in viral load are enough to make a person less contagious in real life.

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