In many countries, the spread of vaccines is rising, but with Covid-19 cases also on the rise and the prospect of another surge of infections on the horizon, the world is in a race against time.
According to experts, the key to winning the race is not only whether the vaccines will play an important role in preventing serious diseases of Covid-19, but whether it can hinder people from spreading the virus.
“The ideal vaccine has two functions: one prevents you from going to the hospital, going to the ICU and losing your life,” said Dr. Peter Hotez, co-director of the Center for Vaccine Development at Texas Children’s Hospital and dean, said. from the National School of Tropical Medicine to the Baylor College of Medicine. “But if the vaccine also stops asymptomatic spread, you could possibly vaccinate your way out of the epidemic.”
Early indications so far have been promising. The effect of vaccines on asymptomatic infection was very unknown, but scientists say it will be crucial to end the pandemic.
It is estimated that more than half of all virus transmissions are responsible for asymptomatic cases, in which people are involved with Covid-19 but have no symptoms, according to a recent study published in the journal JAMA Network Open by researchers from the centers. for the control and prevention of diseases. As such, if vaccines can block asymptomatic infections, it can also significantly reduce overall transmission, offering hope that the virus can occur soon.
Vaccinations can be protected against transmission by reducing a person’s virus load, or how much virus is present in the body, said dr. Becky Smith, associate professor of medicine at Duke University, said.
“Theoretically, by reducing your virus load, it should prevent you from transmitting it to others,” she said. “And even if it does not completely prevent the transfer, it should reduce it significantly.”
The focus on vaccines and transmission comes at an important point in the pandemic. Although business worldwide has been declining for several weeks, some European countries are now seeing a setback. Parts of the US are also reporting an increase, a worrying development, as many states have recently eased public health restrictions.
Concerns about Covid-19 variants, including strains that may be more contagious, also persist. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and the country’s leading expert in infectious diseases, told Richard Engel on Thursday that the US should vaccinate as many people as possible to prevent further outbreaks.
Part of the strategy depends on the effect the vaccine may have on reducing the transmission.
Last week, new data from Israel, where nearly 60 percent of the country’s 9 million residents received at least one dose of vaccine, suggested that the Pfizer-BioNTech vaccine was 94 percent effective in preventing asymptomatic infections.
A separate study by researchers at the University of Cambridge, in the UK, found that a single dose of Pfizer vaccine can reduce asymptomatic infections by 75 percent. The results, which have yet to be judged by peers, come from an analysis of about 4,400 tests done on vaccinated health workers in Cambridge over a two-week period in January.
In Johnson & Johnson trials, the company’s vaccine was found to be 74 percent effective against asymptomatic infections. And according to a report released by the Food and Drug Administration in December 2020, early data suggested that Moderna’s vaccine could also protect against asymptomatic infections, but the company said more research is needed.
Angela Rasmussen, a virologist at the Georgetown University Center for Global Health Science and Security, said these early findings were ‘very promising’. But she added that there are still big unanswered questions.
“From the actual data we have so far, it appears that the vaccines have an impact on asymptomatic infection,” she said. “The real question, though, is how wide will it be?”
And because vaccines are not 100 percent effective, it is possible that a small number of vaccines could become infected with the virus. If this does happen, and an individual who has been vaccinated is asymptomatic, it is not yet known whether the person can spread Covid-19 to others, Rasmussen said.
In a new commentary published in the journal Science on Thursday, Rasmussen and Saskia Popescu, an epidemiologist of infectious diseases at George Mason University, explained why controlling ‘asymptomatic transmission’ is critical to ending the pandemic. . Asymptomatic transmission includes both people who have no symptoms and those who are pre-symptomatic but later develop symptoms.
“As more people are vaccinated, it will have a population effect on transmission, but although the majority of people are not currently vaccinated, we need to address the problem of asymptomatic and pre-symptomatic transmission,” Rasmussen said.
Most scientists agree that there are two main pathways to the pandemic: one involves reaching a threshold known as herd immunity – when enough people have developed antibodies due to natural infections or through vaccines, it is unlikely that future outbreaks will occur. The other one must control the spread of the virus so much that even unvaccinated sections of the population have a small risk of becoming infected.
If vaccines can protect against asymptomatic infection, it can help with the latter, but the two strategies should not exclude each other, Rasmussen said.
“It really is a series of interventions,” she said. “We need to think of ways to reduce transmission in general, and we do not have to rely solely on the vaccines.”
One way to ward off overall proliferation is to heed public health measures imposed throughout the pandemic, such as dissociating oneself from society, wearing a mask, and avoiding meetings with non-vaccinated people. If the virus can be adequately limited, aspects of life could become more normal, even if parts of the population have not yet been vaccinated, Rasmussen said.
“We do not have to be at the threshold immunity threshold to relax restrictions,” she said. “If we can prevent the virus from being so uncommon in the population, there is no risk of people being exposed to it, whether they have been vaccinated or not.”