Two recent studies from Israel and Qatar confirm that the immune protection offered by Pfizer’s COVID-19 vaccine decreases after two months or so. However, protection against severe disease, hospitalisation and death remains strong.

Published in the New England Journal of Medicine, the study says that even fully vaccinated people need to maintain precautions against infection. 

The study from Israel covered 4,800 health care workers. It showed that the antibody levels drop off rapidly after two doses of vaccine “especially among men, among persons 65 years of age or older, and among persons with immunosuppression.”

The researchers highlighted that the levels of neutralising antibodies correlate with protection against infection. However, this study only focussed on antibody levels.

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The researchers wrote, “Published work about many vaccines, such as those against measles, mumps, and rubella, has shown a small decrease each year of 5 to 10% in the neutralising antibody levels.”

“We found that a significant and rapid decrease in humoral response to the BNT162b2 vaccine was observed within months after vaccination.”

The study further highlighted that immunity for people who get vaccinated after natural COVID-19 infection lasts longer. Also, it is especially strong for people who recovered from infection and then got vaccinated.

“Overall, the accumulating evidence from our study and others shows that long-term humoral response and vaccine effectiveness in previously infected persons were superior to that in recipients of two doses of vaccine,” the researchers wrote.

The study from Qatar focussed on actual infections among the highly vaccinated population of that small Gulf nation. People there mostly got Pfizer/BioNTech’s vaccine. 

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Laith Abu-Raddad of Weill Cornell Medicine-Qatar and colleagues wrote, “BNT162b2-induced protection against infection builds rapidly after the first dose, peaks in the first month after the second dose, and then gradually wanes in subsequent months.”

The waning appears to accelerate after the fourth month, to reach a low level of approximately 20% in subsequent months,” they added.

The researchers said that protection against hospitalsation and death stayed at above 90 per cent.