Recent Lancet study sheds more light on natural immunity and vaccine induced protection
The systematic review and meta-analysis included 65 studies from 19 countries including India.
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Protection pre-Omicron variant infection offers
The study found that infection from a pre-Omicron variant--ancestral, alpha, beta, and delta variants-- protected against reinfection from pre-Omicron variant by about 85%; which fell down to 79% within 10 months.
"Protection from past infection against reinfection from pre-omicron variants was very high and remained high even after 40 weeks," it says.
Protection against Omicron variant reinfection
This protection was comparatively less for "the omicron BA.1 variant and declined more rapidly over time than protection against previous variants" the study found.
The protection of a pre-Omicron variant infection against reinfection from Omicron BA.1 was 74% at first month and this protection waned to 36% by 10 months.
However, infection from the Omicron variant provided a higher level of protection against Omicron reinfection. "In general, the findings for omicron sub lineages showed significantly reduced protection when the past infection was pre-omicron. When the past infection was omicron, protection was maintained at a higher level, although less so for BA.4 and BA.5, confirming the greater immune escape associated with this sublineage."
Protection from severe disease
The study finds that though the Omicron and pre-Omicron variants offer different levels of protection against cross infections, they offer a high level of protection against severe diseases.
The mean effectiveness of all the variants against severe diseases which includes hospitalization and death was found to be greater than 78%.
The protection level remained more than 88% even after 10 months.
The protection against severe disease remained high for all variants, with 90·2% for ancestral, alpha, and delta variants, and 88·9% for omicron BA.1 at 40 weeks.
Protection to past infection equivalent to that provided by two-dose mRNA vaccines
Our findings confirm that past infection affords significantly reduced protection against re-infection by the omicron BA.1 variant compared to previous variants, highlighting the high immune escape features of this variant, the researchers have said.
"Our finding that the level of protection from past infection by variant and over time is equivalent to that provided by two-dose mRNA vaccines has important implications for guidance regarding the timing of vaccine doses, including boosters," they have added.
After November 14, 2022, 46% of the global population are estimated to have been infected by Omicron variants
Omicron is the dominant variant of the coronavirus right. By November 14, 2022, almost a year after the variant took over its predecessor Delta, almost 3.8 million people, which is 46% of the global population, were infected by the Omicron variant.
The researchers identified 65 studies from 19 different countries- Austria, Belgium, Brazil, Canada, Czechia, Denmark, France, India, Italy, Netherlands, Nicaragua, Norway, Qatar, Scotland, South Africa, Sweden, Switzerland, the UK, and the USA for the review and meta analysis.