Study Proves Fully Vaccinated People Are Less Likely To Give You COVID – But Which Vaccine Is Better At Preventing Transmission?

Study Proves Fully Vaccinated People Are Less Likely To Give You COVID – But Which Vaccine Is Better At Preventing Transmission?

According to a new study, those who have received the COVID-19 vaccine are less likely to spread the virus even if they get infected themselves!

Furthermore, there seems to be more and more evidence that getting the shot also helps reduce the transmission of the more dangerous delta variant.

Scientists from University of Oxford, United Kingdom, have run this study that involved the records of almost 150,000 contacts traced from about 100,000 initial cases at the national level.

It included vaccinated people, both partially and with both doses of either Pfizer or AstraZeneca, as well as unvaccinated people.

The researchers were, therefore, able to observe how the vaccines affected the transmission of the COVID-19 virus when someone had a breakthrough infection with either the delta or alpha variant.

It was able to show that both vaccines were more effective against the alpha variant than the delta one.

More precisely, if someone was exposed to an infected but vaccinated person, they were 65 percent less likely to get the virus themselves if the contact had received both shots of the Pfizer vaccine.

As for those fully vaccinated with AstraZeneca, they were 36 percent less likely to infect someone else upon contact.

On the other hand, the risk of contracting the virus from someone vaccinated with only the first dose was significantly higher.

While this study was just recently shared online and is yet to get peer-reviewed at this time, other scientists not involved in the research and, therefore, unbiased have stressed that the results are reliable.

Infectious disease physician from the University of Pennsylvania, Dr. Aaron Richterman, for instance, stated about the study that “It’s the highest quality study we have so far on the question of infectiousness of vaccinated people infected with delta.”

Furthermore, clinical microbiologist at the University of Southern California, Susan Butler-Wu, praised the research by calling it “well performed.”

By using cycle threshold (Ct) values, the scientists involved in the study were able to find a pretty similar level of viral load in both vaccinated and unvaccinated people as far as the much more contagious delta variant is concerned.

However, in spite of this, those fully vaccinated were still less likely to transmit the variant to others than those unvaccinated.

It is possible that vaccinated people are able to combat the virus in their bodies easier and faster upon infection.

This further confirms other similar studies previously done and which had reached the same conclusions.

For example, a study from Singapore determined that, even though the virus levels were the same initially, no matter the vaccine status of delta infectees, only a week later, the situation was very different.

By day 7, levels of the virus had dropped significantly, which suggests that vaccination is able to reduce the spread power of the variant.

Richterman stated that vaccines are able to prevent transmission of the virus in two different ways.

The first one is, of course, by preventing infection as much as possible, while the other is by reducing the amount of infection in your body in the case that you do still test positive for COVID.

“People who have been vaccinated will have immune systems at the ready that can coat the virus in antibodies much more quickly than unvaccinated people who have to build up an immune response,” Richterman explains.

At the same time, however, the study also showed that the vaccines are definitely time-sensitive to a certain extent.

After only three months since being vaccinated with AstraZeneca, the subjects became just as likely to spread the variant as those unvaccinated.

On the other hand, the Pfizer vaccine seems to be more effective and for a longer period of time.

The level of protection, in this case, decreased after three months as well, but the study proved there was still an advantage for those who had received both doses of the Pfizer vaccine as opposed to those unvaccinated.

Richterman pointed out that a reduction in protection against the spread is actually not a shock as antibody levels tend to decrease in time following any vaccination.

“We know that the amount of antibodies circulating in the blood decreases over time after vaccination, even though the immune memory remains durably robust and is still able to prevent infections, particularly severe infection. These circulating antibodies that are immediately available probably play some role in preventing transmission if infected, so I don’t think it’s surprising to see some reduced protection against transmission over time.”

Butler-Wu agreed and went on to stress that while transmission levels are still high, getting tested and wearing masks is just as important as getting vaccinated.

“We need to combine our vaccines with other measures to reduce how much virus we get exposed to by things like masking and testing. Additive measures is the name of the game here,” she stated.


Katherine is just getting her start as a journalist. She attended a technical school while still in high school where she learned a variety of skills, from photography to nutrition. Her enthusiasm for both natural and human sciences is real so she particularly enjoys covering topics on medicine and the environment.

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