COVID infections in vaccinees: how common is it?

By Dennis Thompson Health Day Reporter

TUESDAY July 6, 2021

People who suffer from a rare ‘breakthrough’ coronavirus infection after receiving the Pfizer or Moderna vaccine will not get as sick and, most importantly, are much less likely to pass the coronavirus to others, according to a new study.

It is very unlikely that a person would be infected with COVID-19 after receiving any of the messenger RNA (mRNA) vaccines, which provided 91% effective protection among the vaccinated people included in this study.

But those who contracted COVID-19 despite being vaccinated ended up showing milder symptoms over a shorter period of time compared to those who were not inoculated, researchers reported on July 1 in the New England Journal of Medicine.

Vaccinated people who caught COVID-19 also had a 40% lower viral load during their infection, compared to unvaccinated people.

“If you were at least partially vaccinated, you had less virus in you for a shorter period of time than those who had not been vaccinated, meaning they would be less likely to pass the virus on to someone else. other, “said researcher Dr. Jefferey Burgess, associate dean for research at the College of Public Health at the University of Arizona, Tucson.

According to Dr. Amesh Adalja, a senior researcher at the Johns Hopkins Center for Health Security in Baltimore, the results “should give people a lot of confidence about COVID-19 vaccines. When the very rare breakthrough infections do occur, they are really not clinically significant, as the severity and infectivity are dramatically reduced, even in individuals who are not fully vaccinated. “

The study involved 3,975 health workers, first responders, and other essential and frontline workers who were prioritized to receive an mRNA vaccine. Participants included 3,179 adults who received one or two injections, as well as 796 people who were not vaccinated.

The researchers followed all of these people from mid-December to mid-April to determine the effectiveness of the Pfizer and Moderna vaccines.

Pretty good, as it turns out. Out of the group as a whole, 156 unvaccinated people were infected with COVID-19, compared to just five fully vaccinated people and 11 partially vaccinated people.

A full two-dose course provided 91% protection, and even a single dose gave 81% protection, the researchers calculated.

If a vaccinated person was infected with COVID-19, they were 58% less likely to have a fever or chills, according to the results.

Instead, they typically had cold-like symptoms (like sniffles), spent an average of two days less in bed, and had an overall illness duration that was six days shorter than people who avoided the vaccination. .

This study took place before the advent of the Delta variant, which is 50 to 80 times more transmissible than the original Alpha strain of COVID-19, noted Dr Tina Tan, professor of pediatric infectious diseases at the Feinberg School. of Medicine at Northwestern University. , in Chicago.

Burgess couldn’t say how the new strain would impact the protection reported in the study.

“I’m a little hesitant to take any risks because we are still learning about the Delta variant,” said Burgess. “I can say that from what I have seen in other studies, two doses of these messenger RNA vaccines protect against the Delta variant.”

Adalja issued a more confident note regarding the protection of the mRNA vaccine against Delta.

“I don’t think the Delta variant is a problem for vaccines, and those who develop rare infections after vaccination are likely to have clinically insignificant disease that is not contagious,” Adalja said.

More information

The US Centers for Disease Control and Prevention has more on COVID-19.

SOURCES: Jefferey Burgess, MD, MPH, associate dean, research, University of Arizona College of Public Health, Tucson; Amesh Adalja, MD, senior researcher, Johns Hopkins Center for Health Security, Baltimore; Tina Tan, MD, professor, pediatric infectious diseases, Feinberg School of Medicine at Northwestern University, Chicago; New England Journal of Medicine, June 30, 2021

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