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The one ‘puzzle’ that seems still unsolved even after >16 months of the pandemic is, “Which provides superior protection: Natural infection or Vaccines?” Many studies have been conducted in this regard, but no clinching evidence in favour or against the two is still available 1/
I along w/ my wife got infected w/ Covid19 in Sept’20. I had a mild-mod disease whereas she had the only mild illness. We are monthly following with our anti-spike IgG levels. The following graph shows the IgG levels at monthly interval. No reinfection infection so far 2/
A recent study with #Pfizer vaccine finds that protection remains at least 6 months without much change in the vaccine efficacy level (95% Vs 91%) 3/
https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-confirm-high-efficacy-and-no-serious
https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-confirm-high-efficacy-and-no-serious
Similarly, #Moderna vaccine finds protection lasting at same length without much change in numbers 4/ https://www.businesstoday.in/sectors/pharma/moderna-vaccine-antibodies-last-at-least-6-months-shows-study/story/436275.html
But, ‘breakthrough’ cases (vaccine failure) are seen in the fully vaccinated US citizens & 7% of these 5800 cases had severe disease. Duration of observation following vaccination varies… 5/ https://edition.cnn.com/2021/04/14/health/breakthrough-infections-covid-vaccines-cdc/index.html
However, with AZ vaccine it is noticed that anti-Spike IgG Abs last for 6 months after a single dose. However, the titters dropped 64% by 180 day 6/ https://pubmed.ncbi.nlm.nih.gov/33617777/
Apart from the above listed studies, I did not find much evidence on the longevity of vaccine-induced protection. 7/
Now let’s see how long immune protection following a natural #SARSCoV2 infection lasts. One of the most recent study by @profshanecrotty concludes that immunological memory to SARS-CoV-2 lasts at least for up to 8 months after infection 8/ https://science.sciencemag.org/content/371/6529/eabf4063
One recent large longitudinal study among 25 661 HCWs ( #SIREN Study) after 7 months follow up finds 84% lower risk of re-infection in already infected; 93% reduction in symptomatic infections; No effect of B.1.1.7 9/ https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00675-9/fulltext
Another study by #ICMR on #reinfections: 1300 cases tested +ve twice; Only 58 (4.5%) cases found as possible reinfections. 102 days w/ a negative result in between a must; Genome analysis done to confirm diff viral infections 10/ https://www.livemint.com/news/india/icmr-study-finds-covid-19-reinfection-in-4-5-cases-11617286851986.html
Danish study on reinfections: Natural infection with #SARSCoV2 led to observed protection ag reinfection approx 80% after 6 months. Estimated protective immunity to be approx 80–83% in people <65 yrs; low natural immunity > 65 yrs & older 11/
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00575-4/fulltext#:~:text=Through%20analysis%20of%20Danish%20population,immunity%20over%20the%20study%20period.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00575-4/fulltext#:~:text=Through%20analysis%20of%20Danish%20population,immunity%20over%20the%20study%20period.
