Understanding COVID-19 Immunity- Recent research published in The Lancet has provided new insight into the strength and duration of natural immunity to COVID-19 by variant. By analyzing data from 65 studies across 19 countries, this was the largest review ever conducted on this topic to date. The researchers sought to determine whether infection resulted in similar protection against reinfection with different variants, or if this protection waned over time.
The study revealed that prior infection was highly protective against reinfection with alpha, beta and delta variants of Omicron BA.1, though less so against omicron BA.1.
On average, prior infection provided moderate protection from reinfection with Omicron BA.1 (45%), while pre-omicron variants offered stronger protection (82%). Over a 40 week period however, protection against reinfection for pre-omicron variants declined rapidly to 78.6%; conversely for omicron BA.1, it decreased more rapidly to 36.1 per cent.
However, the study revealed that protection against severe disease following natural infection was comparable to that achieved from two vaccine doses for both pre-omicron and omicron BA.1 variants.
This finding implies that one’s previous infection status and timing should be taken into account alongside their booster vaccinations in order to accurately predict protection.
The study also highlighted the critical role of T cells in combatting COVID-19. Unlike antibodies, they recognize fragments of virus proteins rather than entire ones, making it harder for viruses to avoid T cell immunity after infection. T cells therefore provide a crucial last line of defense when other immune mechanisms may have failed during infection.
Although natural infections may offer similar protection to vaccination, the authors stress that SARS-CoV-2 remains a dangerous and unpredictable virus. Their results could inform when to initiate booster vaccination strategies; however, further high-quality long-term follow-up studies are needed to confirm these conclusions.
This study, published in The Lancet, examined data from 65 studies across 19 countries – making it the largest review on natural immunity to COVID-19 yet. Researchers compared COVID risk between people who had already been infected and those without, to see if infection induced similar protection against reinfection with different variants and whether that protection waned over time.
Researchers discovered that prior infection was highly protective against reinfection with alpha, beta, and delta variants but less so against omicron BA.1. Only 45 per cent of previous victims experienced protection from reinfection with omicron BA.1; however this protection was significantly greater against pre-omicron variants at 82 per cent.
Surprisingly, the study also discovered that protection against severe disease after natural infection was comparable to that received from two vaccine doses for both pre-omicron and omicron BA.1 variants. This is encouraging news for those who have already taken COVID-19, as it suggests they are less likely to experience future episodes of severe illness.
However, the authors cautioned that protection against reinfection with omicron BA.1 drops more rapidly over time than with pre-omicron variants. Data from long-term studies revealed that protection against reinfection for pre-omicron variants decreased to 78.6% after 40 weeks, whereas for omicron BA.1, protection declined even faster to 36.1 per cent.
The study’s results make sense when we consider how omicron variants differ from their predecessors. Omicron lineages contain enough mutations to differentiate significantly from previous varieties and thus avoid existing antibodies, explaining why we were unable to prevent reinfection with these omicron variants.
Thankfully, a study published recently revealed that T cells, an immune cell type, can recognize fragments of virus proteins rather than entire viruses. This means it would take many more mutations in omicron’s genome for it to completely avoid T cell immunity.
Unlike antibodies, T cells don’t seek out viruses but rather identify infected cells and quickly eliminate them to reduce virus factories within the body. Thus, having strong T cell responses after infection is crucial in preventing severe illness caused by coronaviruses – something Omicron may try harder to avoid.
Though a natural infection may offer similar protection to vaccination, the authors caution that seeking out SARS-CoV-2 infection is not recommended. This virus remains highly infectious and unpredictable, with potential long-lasting negative effects that could linger long after recovery.
Overall, this study offers important new insight into the strength and duration of natural immunity to COVID-19 by variant. It suggests that protection against reinfection with omicron is less robust than with previous variants, yet T cells play an integral role in preventing severe disease. Further long-term follow up studies are necessary to confirm these results as we learn more about how best to safeguard ourselves against this rapidly evolving virus.
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