Having two doses of a COVID-19 vaccine has been linked with negative protection against symptomatic infection from the disease, while a previous infection without vaccination offers around 50 percent immunity, according to data from a study by Weill Cornell Medicine in Qatar.
The study, published in the New England Journal of Medicine on June 15, examined the Omicron wave in Qatar that occurred from around December 2021 to February 2022, comparing vaccination rates and immunity among more than 100,000 Omicron infected and non-infected individuals.
The authors concluded that: “no discernable differences in protection against symptomatic BA.1 and BA.2 infection were seen with previous infection, vaccination, and hybrid immunity. Vaccination enhanced protection among persons who had had a previous infection. Hybrid immunity resulting from previous infection and recent booster vaccination conferred the strongest protection.”
Their data indeed demonstrated that hybrid immunity, developed through a previous infection and vaccination had the strongest immunity over time.
However, their 6-month data comparing individuals that were only vaccinated to those that have only been previously infected tells a more nuanced story between natural and artificial immunity.
Only Previous Infection Compared to Only Vaccination
The authors of the study found that those who were only infected had a more sustained immunity against COVID-19 symptoms over time as compared to individuals that were only vaccinated.
People that were previously infected had the highest starting immunity against symptomatic infections of at least over 60 percent, with a sustained immunity at around 50 percent even after 6 months.
Whereas, a double-dosed vaccination gave a weak effectiveness of around 40 percent within three months after administration, with the immunity following into negative regions of immunity, indicating an increased risk of symptoms.
Six months after getting two doses of the Pfizer vaccine, immunity against Omicron symptoms gradually dropped to -3.4 percent, below an average person without infection and vaccination (control) which would be set at 0.
For two doses of the Moderna vaccine, immunity against Omicron symptoms dropped to -10.3 percent after more than six months since the last injection.
Though authors wrote in the study that three doses of vaccination had a stronger immunity of over 50 percent. It should be noted that this average was taken at only 42 days after the third vaccination, looking at the decreasing trend in effectiveness over 1 month, it is plausible to speculate that immunity is likely to drop further over time.
In comparison, previous infection gave 50 percent immunity, even over 300 days after the infection, which is a far stronger, and more sustained immunity.
‘Natural Immunity Wins Again’
These findings are supported by another recent study from Israel that also found natural immunity waned significantly more slowly compared to artificial, or vaccinated, immunity.
The study found that both natural and artificial immunity waned over time.
Individuals that were previously infected but not vaccinated had half the risks of reinfection as compared to those that were vaccinated with two doses but not infected.
“Natural immunity wins again,” Dr. Martin Adel Makary, a public policy researcher at Johns Hopkins University, wrote on Twitter, referring to the Israeli study.
“Among persons who had been previously infected with SARS-CoV-2, protection against reinfection decreased as the time increased,” the authors concluded, “however, this protection was higher” than protection conferred in the same time interval through two doses of the vaccine.
Enrico Trigoso contributed to this report.
Correction: This article has been updated to include the study’s official conclusions.