Covid-19: New study to probe whether vaccinated people can still spread the virus

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  • The Covid-19 vaccines were designed to protect individuals against Covid illness
  • However, whether the shots can prevent viral spread is not yet clear
  • A new college campus study, focusing on the Moderna vaccine, will attempt to answer this question

If you’ve been vaccinated against Covid-19, you’re likely aware that while you may be protected against severe Covid illness should you encounter the virus, it, unfortunately, isn’t a free pass to go back to living your life pre-pandemic.

Instead, health agencies have advised that vaccinated individuals should continue to follow public health protocols, including wearing a face mask when out in public. This is because experts are still learning how the vaccines will affect the spread of SARS-CoV-2, the virus that causes Covid disease.

“Until we know more about how vaccines will affect the spread of Covid-19, people who are fully vaccinated against Covid-19 should keep taking precautions in public places like wearing a mask, staying 6 feet (1.8m) apart from others, avoiding crowds and poorly ventilated spaces, and washing your hands often,” notes the US Centers for Disease Control and Prevention (CDC).

A new college campus study, called PreventCOVIDU, will attempt to directly answer this crucial question through contact tracing. According to Harvard Health, contact tracing begins with identifying everyone that a person recently diagnosed with Covid came in contact with after becoming contagious.

In this new study, Covid infections will be tracked among vaccinated people who receive the Moderna vaccine, unvaccinated people, and a large group of close contacts.

“We already know that this vaccine can prevent serious Covid-19 disease, but we do not know if the vaccine will prevent the virus from shedding from the nose and mouth and infecting others. That is what we are testing in this study,” according to the study's recruitment website.

Designing a transmission study

Earlier this year, Professor Glenda Gray, president of the South African Medical Research Council (SAMRC), explained that none of the Covid vaccine clinical trials to date has looked at transmission of the virus after vaccination, but have solely focused on whether the jabs protect the individual against Covid illness.

“When you design a transmission study, you design a different study. None of the vaccine studies has done a transmission study," she said.

To understand how well the vaccine works at preventing transmission of the virus, mass vaccinations would have to take place, and one could then infer based on that data, such as is the case in Israel – either that or a transmission study would have to be designed.

Gray explained that this kind of study could be done at universities, where one university group is vaccinated and the other isn’t, and then compare the data. “It’s a complicated study but they are being designed at the moment,” she added.

Real-world studies in Israel, where the population was vaccinated with the Pfizer-BioNTech jab, are suggestive that the vaccines may reduce the risk of both infections, but these kinds of studies are not conclusive evidence. 

About the campus study

The federally-funded PreventCOVIDU study will take place across 21 college campuses and will include 12 000 university students aged 18 to 26, according to the site.

"This study is addressing the important issue about what does it mean to be vaccinated, as far as your risk for transmitting SARS-CoV-2 to people in your bubble of trust," Dr Lilly Immergluck, a paediatric infectious-disease specialist at Morehouse School of Medicine in Atlanta, told the Washington Post.

The participants will be randomly split into two groups. Half of the group will receive their first Moderna vaccine dose immediately, and the other half will be vaccinated four months later. The students will then each identify “close contacts” (about 25 000 people in total) who will also be invited to take part in the trial.

The site explains that a phone app will remind the participants to swab their noses daily for two weeks. In addition, they will complete daily questionnaires about their symptoms, potentially provide two blood samples, and undergo routine Covid screenings through their university testing systems.

Results expected in 2021

The study will take place over a five-month period, and results are expected later this year.

These results, the researchers point out, are critical to explain the extent to which the vaccine may prevent asymptomatic (displaying no symptoms) infection and transmission of the virus.

“With the US having the highest number of infections and deaths from Covid-19 disease of any nation in the world, this study is vital to making informed public policy decisions in the coming year,” the researchers say.

“Should the vaccine be found to work primarily by reducing symptoms – preventing severe disease and saving the lives of those vaccinated but not curbing ongoing viral transmission – studies project that the number of asymptomatic infections could rise, which would increase transmission and prolong the pandemic.”

*For more Covid-19 research, science and news, click here. You can also sign up for our Daily Dose newsletter here.

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