The National Pulse converts these numbers into percentages: “Regarding positive PCR tests, within the first 10 days of contracting the virus 68.75 percent of unvaccinated subjects were no longer contagious. The National Pulse article cites only data on the number of people PCR-positive at each time point to assert that “individuals who did not receive a COVID-19 vaccine were contagious for a shorter period of time.” The study graph shows, for example, that at day 10, one of the 16 unvaccinated people remained PCR-positive, as did eight of the 37 vaccinated people and one of the 13 boosted people.
The median time to a negative virus culture from whichever was earlier – symptom onset or the initial positive PCR test - was six days with Delta and eight days with Omicron. The median – meaning half the group took longer, half took less – time from the first positive PCR test until a negative PCR test was four days in the Delta group and five days in the Omicron group. On average, the study found, Omicron and Delta infections had similar durations. The study examined how many days it took from the initial positive PCR test, and from symptom onset, until people had a negative PCR test and until they had a negative virus culture. At the time of their COVID infections, 16 people were unvaccinated, 37 had received the primary vaccine series, and 13 had also received a booster shot. Of these, 34 people had been infected by the Delta variant and 32 by Omicron. Genome sequencing of the samples was also done to identify which virus variant an individual carried.įor their published analysis, the researchers included a total of 66 people. “Viral culture is a marker of contagiousness, with the presumption that the virus still needs to be alive to be able to be transmitted.” PCR testing “measures whether there is any virus detected in the nasal swabs, irrespective of whether it is alive or dead,” Siedner explained. Each sample was tested by PCR for detectable virus, and cultured in the lab to see if the virus was potentially infectious. The researchers had recruited people newly diagnosed with COVID-19 by PCR test in the Mass General Brigham medical system between June 2021 and January 2022, and asked each person to provide multiple additional nasal swab samples, three times a week, for a total of two weeks. In study graphs, the researchers chart the proportions and the actual numbers of individuals infected with either virus variant who remained PCR positive or viral-culture positive at 5, 10, and 15 days after their initial positive PCR test.
Viral culture, not PCR-positivity, gauges the potential for virus to be contagious. The article also highlights the wrong data to make its point. The article shared by Kheriaty on Twitter takes one piece of the NEJM study’s data out of context and “distorts it,” said study co-author Amy Barczak, MD, also affiliated with Mass General. The headline of an article published by, reading, “New England Journal of Medicine: Unvaccinated COVID Patients Are Contagious for LESS Time Than Those Vaxed or Boosted,” was posted by Aaron Kheriaty, MD ( here) with a link to that article and the comment, “Gosh, I mean, who would have thought?” The tweet has been shared more than 14,000 times. “Quite the contrary: we found no significant difference by vaccination status (unvaccinated, vaccinated or boosted) in the time from a first positive test until PCR testing or viral cultures from nasal specimens became negative.” “Our data do not suggest that vaccinated people recover more slowly from COVID-19,” Siedner added. “In all three groups, less than 10% were still culture positive at that time,” he said by email. There were also no differences between groups in the proportion with a positive viral culture at 10 days, study co-author Mark Siedner, MD, of Massachusetts General Hospital in Boston, told Reuters. In fact, the study published online in late June by NEJM ( here), found that the median duration of infectiousness (potential to pass on the virus) - as measured by the ability to grow virus in culture from nasal samples - was seven days among the unvaccinated, and six days among both the vaccinated and boosted groups, according to one of the study authors. A widely shared Twitter post and the article to which it links misleadingly suggest that results of a small study published in the New England Journal of Medicine show vaccinated people remain contagious with a COVID-19 infection longer than unvaccinated people.
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