'Very promising' data shows vaccines may stop Covid transmission, but big questions remain

The spread of vaccines is increasing in many countries, but with Covid-19 cases rising again and the prospect of a further surge in infections on the horizon, the world is in a race against time.

Experts say the key to winning the race is not only whether the vaccines play an important role in preventing serious diseases from Covid-19, but whether they can stop people from spreading the virus.

“The ideal vaccine would have two characteristics: One would prevent you from going to the hospital, going to intensive care and losing your life,” said Dr. Peter Hotez, co-director of the Center for Vaccine Development at Texas Children’s Hospital and Dean of the National School of Tropical Medicine at Baylor College of Medicine. “But if the vaccine also stops the asymptomatic spread, you could potentially vaccinate yourself out of the epidemic.”

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Early signs so far have been promising. The effect of vaccines on asymptomatic infections was a great unknown, but scientists say it will be crucial in ending the pandemic.

It is estimated that asymptomatic cases involving people infected with Covid-19 but showing no symptoms account for more than half of all transmissions of the virus. This is evident from a study recently published in the study JAMA Network Open magazine by researchers from the Centers for Disease Control and Prevention. If vaccines can block asymptomatic infections, they could also significantly reduce overall transmission, which gives hope that the virus may be included soon.

Vaccines can protect against transmission by reducing a person’s viral load or how much virus is in the body, said Dr. Becky Smith, associate professor of medicine at Duke University.

“In theory, reducing your viral load should prevent it from spreading to others,” she said. “And even if it doesn’t completely prevent transmission, it should be reduced significantly.”

The focus on vaccines and transmission comes at an important time in the pandemic. Although cases worldwide decreased for several weeks, some The European countries are now experiencing a recovery. Parts of the USA also report upward movements, a worrying development as many states recently eased public health restrictions.

Concerns about variants of coronavirus, including contagious strains, also persist. The government’s leading infectious disease expert Dr. Anthony Fauci, director of the National Institute for Allergies and Infectious Diseases, told NBC News’ Richard Engel on Thursday that the US needs to vaccinate as many people as possible to avoid further outbreaks.

Part of this strategy depends on the effect of the vaccine on reducing 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 it was the Pfizer BioNTech vaccine 94 percent effectively prevent asymptomatic infections.

A separate one Study conducted by researchers from Cambridge Universityin the UK it was found that a single dose of the Pfizer vaccine can reduce asymptomatic infections by 75 percent. The results, which have not yet been peer-reviewed, come from an analysis of around 4,400 tests carried out on vaccinated health care workers in Cambridge in January over a two-week period.

Johnson & Johnson’s studies found that the company’s vaccine was 74 percent effective against asymptomatic infections. And after a Report published in December According to the Food and Drug Administration, early data suggests that Moderna’s vaccine may also protect against asymptomatic infections. However, the company has determined that further investigation is needed.

Angela Rasmussen, a virologist at Georgetown University Center for Global Health Science and Safety, said the initial results are “very promising”. But she added that there are still some big unanswered questions.

“From the real world data we have so far, it appears that the vaccines have an impact on the asymptomatic infection,” she said. “The real question, however, is how broad that will be.”

And because vaccines are not 100 percent effective, a small number of people who have been vaccinated may become infected with the virus. If this happens and a vaccinated person is asymptomatic, it is not yet known whether the person could transmit Covid-19 to others, Rasmussen said.

In a new comment published Thursday in the journal ScienceRasmussen and Saskia Popescu, infectious disease epidemiologist at George Mason University in Virginia, explain why controlling “symptom-free transmission” is critical to ending the pandemic. Asymptomatic transmission includes people who have no symptoms as well as people who are presymptomatic but develop symptoms later.

“If more people are vaccinated, it will have a population-wide impact on transmission. Although the majority of people are currently not vaccinated, we must be aware of the problem of asymptomatic and pre-symptomatic transmission,” said Rasmussen.

Most scientists agree that there are two main paths out of the pandemic. One is reaching a threshold known as herd immunity – if enough people have developed antibodies to natural infections or vaccines, future outbreaks are unlikely. On the other hand, the spread of the virus must be restricted to such an extent that even non-vaccinated parts of the population have only a low risk of infection.

If vaccines can protect against asymptomatic infections, they could help with the latter, but the two strategies shouldn’t be mutually exclusive, Rasmussen said.

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“It’s really a series of interventions,” she said. “We need to think about ways to reduce overall transmission and we don’t have to rely solely on the vaccines.”

One way to reduce overall transmission is to consider public health measures taken during the pandemic, such as: B. practicing social distancing, wearing masks and avoiding gatherings with unvaccinated people. If the virus can be properly contained, aspects of life could return to normal even if sections of a population are not yet vaccinated, Rasmussen said.

“We don’t have to be on the cusp of herd immunity to relax restrictions,” she said. “If we can make the virus so uncommon in the population, there is no risk that people will be exposed to the virus whether they are vaccinated or not.”

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