The researchers compared prior COVID-19 infections, vaccination immunity, and permutations thereof among more than a hundred thousand Omicron-infected and non-infected people in the study, which was published on June 15, 2022, in the New England Journal of Medicine.

The results showed that complete mRNA vaccination plus a booster dosage, together with natural immunity from infection by an earlier version, provided the best protection against Omicron infection. On the other hand, vaccine resistance against new infections appeared to decrease quickly, whereas people who had a prior-variant infection were somewhat protected against Omicron, with no decline in resistance even a year later.

The study, which was the first of its kind to look into possible permutations of immune function for Omicron coronavirus variant SARS-CoV-2 infections, uncovered evidence that both vaccination and preceding infection presented strong and long-lasting coverage against drastic, critical, or potentially lethal COVID-19 diseases when the Omicron wave was ongoing. 

Qatar’s unified and consistent e-health database, which contains all SARS-CoV-2 RT-PCR experiments run in the country, allows for extraordinarily quick and sizable epidemiological research. Dr. Abu-Raddad and collaborators had already published high-profile articles on SARS-CoV-2 infection and disease rates for previous variations and waves.

The researchers compiled a list of positive PCR tests linked to infection signs in Qatar during the nation’s omicron (B.1.1.529) phase. They matched each of these contaminated, symptomatic people with a PCR-negative person from the database, based on sex, screening week, age group, as well as nationality. 

The team of researchers next looked into how the two groups’ preceding wave of COVID-19 illnesses and immunization histories differed. A total of 104,490 participants were enrolled in the study. A noteworthy finding was that having received the customary 2 doses of either the Pfizer vaccine or Moderna vaccine but having no preceding infection provided no immunity against symptomatic Omicron disease. 

Although most boosters were given just weeks before the Omicron wave, obtaining a booster dosage looked to be roughly 60% protective. Overall, the findings revealed that mRNA vaccinations and boosters perform reasonably well in guarding against symptomatic Omicron disease. However, their immune response fades quickly and vanishes after six months or so, which is consistent with previous research.

This “natural immunity” was proved to confer around 50% resistance against symptomatic COVID-19 infection during the Omicron wave for those without a history of immunization, and this “natural immunity” was linked with nearly the same level of protection almost a year after the disease.

People with prior infection and full immunization provided the best protection; people with prior virus exposure and 3 vaccine doses of either mRNA were over 80% protected from symptomatic infection during the Omicron wave.

The findings also showed that immunization, the past infection alone or in conjunction with vaccination, was preventative against severe disease from Omicron infections, with the preventive role ranging from roughly 72% for prior infection alone to 100% for prior infection plus 3 doses of COVID-19 vaccine. 

“These results indicate the value of vaccination to patients who have already been infected with the virus for maximum protection to battle against the Omicron COVID-19 variant,” Dr. Abu-Raddad stated.

The study differentiated between viruses caused by two separate Omicron variant sub-lineages, BA.1 as well as BA.2 coronavirus, but showed relatively similar effects for both, including for both Pfizer & Moderna vaccinations.

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