A new peer-reviewed study shows two doses of an mRNA COVID-19 vaccine yield negative protection against symptomatic SARS-CoV-2 infection, while previous infection without vaccination offers about 50% immunity.
The findings, published June 15 in the New England Journal of Medicine (NEJM) analyzed information from more than 100,000 Omicron-infected and non-infected residents in Qatar from Dec. 23, 2021, through Feb. 21, 2022.
The authors compared the effectiveness of the Pfizer and Moderna COVID-19 vaccines, natural immunity from previous infection with other variants and hybrid immunity (a combination of infection and vaccination) against symptomatic Omicron infection and severe, critical and fatal disease.
Researchers found those who had a prior infection but had not been vaccinated had 46.1% and 50% immunity against the BA.1 and BA.2 Omicron subvariants more than 300 days after the previous infection.
However, individuals who received two doses of the Pfizer and Moderna vaccines, but had not been previously infected, had negative immunity against the BA.1 and BA.2 Omicron subvariants — indicating an increased risk of infection compared to someone without prior infection and vaccination.
Six months after the second dose of Pfizer, immunity against any Omicron infection dropped to -3.4% below an average person without infection and vaccination, which as a control, was set at 0.
For two doses of Moderna, immunity against any Omicron infection dropped to -10.3% about six months after the last dose.
The authors said three doses of the Pfizer shot increased immunity to over 50%, but immunity was measured only at a median of 42 days after the third dose, showing a rapid immune decline in a very short period of time.
In comparison, those who had previously been infected had 50% immunity even at 300 days after infection.
After six months, the study showed vaccine efficacy fell to negative figures 270 days after the second dose, predicting more rapidly waning immunity for vaccines compared to natural immunity….