Past COVID infection protects against severe disease: Study

Jolyon Attwooll

17/02/2023 1:46:53 PM

A previous bout of COVID-19 reportedly offers the same protection from hospitalisation and death after re-infection as two mRNA vaccinations.

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Previous COVID infection provides a ‘high level’ of protection against severe disease for all variants, including Omicron.

The arrival of Omicron has led to significantly higher rates of reinfection, but protection from severe disease remains high, according to a new study published in The Lancet.
The systematic review and meta-analysis, entitled ‘COVID-19 infection, reinfection, and the transition to endemicity’, was published this week and is likely to corroborate the experience of many GPs who have had patients experiencing multiple bouts of the disease.
The research shows a substantially diminished level of protection against reinfection or symptomatic disease for the Omicron variant.
It found a substantial level of protection against symptomatic infection, hospitalisation and death, averaging more than 85%, among those previously infected with the ancestral, Alpha, Delta, and Beta variants, whereas protection against Omicron dropped to 55% for symptomatic disease.
However, a more positive finding suggested previous COVID infection provides a ‘high level’ of protection against severe disease for all variants, including Omicron.
One of the limitations of the analysis is that it involved only ‘a small number’ of studies looking at protection from past infection against Omicron sublineages, including BA.2, BA.4 and BA.5.
The authors write that from the findings they could extrapolate, those sublineages showed notably less protection when the past infection was pre-Omicron, but protection was maintained at a higher level from Omicron onwards, although less so for the BA.4 and BA.5 sublineages.  
This confirmed their ‘greater immune escape’, they wrote.
The authors contend that while protection provided by past infection wanes over time, it ‘appears to be at least as durable, if not more so, than that provided by two-dose vaccination with the mRNA vaccines for ancestral, Alpha, Delta, and Omicron BA.1 variants’.
Dr Deborah Burnett from the Garvan Institute of Medical Research said the substantially reduced risk of severe disease following re-infection with COVID-19 represents ‘great news’.
‘This meta-analysis, pooling together the previous findings from many others in the field, highlights that people who have been previously infected with or vaccinated against COVID-19 show a greatly reduced risk of severe disease when re-infected with the virus, even if their secondary infection is a different strain from their original infection,’ she said.
‘However, the ongoing spreading of the virus is still problematic as it still leaves vulnerable populations at risk, and it allows the virus to continue and mutate into newer variants.’
Researchers say their findings have implications for public health settings.
‘The immunity conferred by past infection should be weighed alongside protection from vaccination when assessing future disease burden from COVID-19, providing guidance on when individuals should be vaccinated, and designing policies that mandate vaccination for workers or restrict access, on the basis of immune status, to settings where the risk of transmission is high, such as travel and high-occupancy indoor setting,’ they wrote.
University of Queensland infectious diseases physician and microbiologist Associate Professor Paul Griffin describes the study is a ‘valuable addition’ to existing knowledge. 
‘The obvious difference to keep in mind between protection from vaccination versus that provided by infection is that infection carries with it the risk of disease, including severe disease in a proportion, whereas vaccination does not,’ he said.
‘It is also important to consider that some of the challenges we face with the longevity of protection from vaccination including for example waning over time and immune evasion also apply to protection generated by infection.’
The Bill and Melinda Gates Foundation were among the funders for the research. Its authors wrote that the work is the first review ‘to comprehensively assess natural immunity protection against COVID-19 re-infection by variant and to evaluate waning immunity with time since primary infection’.
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Dr Rodney Paul Jones   18/02/2023 9:00:49 AM

Are there any efficacy/ safety studies comparing non MRNA vs MRNA vaccines ?
Some are deliberately avoiding the latter