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In the seropositive group only 3 reported to have contracted the disease again, of whom 1 was hospitalized without needing oxygen, whereas in the previously seronegative group 127 contracted the infection, of whom 30 hospitalized and 12 amongst dose on oxygen. This study started on Dec 16 and ran apparently until May, hence also mostly before the delta surge.Įp 164-6: Mishra in medRxiv 19 July reports on a telephone research during the delta epidemic in over 2200 subjects, appr 50 % previously found sero-positive and 50 % seronegative for SARS-CoV-2.
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Fig 2, shows indeed that previous infection + full vaccination has no statistical benefit versus previous infection or full vaccination only.Įp 164-5: A similar study published in June in medRxiv amongst 52,000 employees of the Cleveland Clinics also shows no difference in protection between previously infected with or without full mRNA vaccination. The conclusion is that natural infection resulting in detectable anti-spike antibodies and 2 vaccine doses both provide robust protection against SARS-CoV-2 infection, including against the B.1.1.7 variant. Clearly, no data on combined effect of previous infection and vaccination are provided here.Įp 164-4: Lumley CID July 2021: A follow-up amongst 13 109 HCWs 8285 received the Pfizer-BioNTech vaccine (1407 two doses), and 2738 the Oxford-AstraZeneca vaccine (49 two doses) in England at the time of the alpha epidemic.
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The authors conclude that previous infection protects at least equally as vaccination. Of those 254 occurred in the 4313 SARS-naive and unvaccinated group, 4 in the 739 mRNA vaccinated and 0 in the 254 previously infected subjects. Note that the delta variant was not yet dominant in May, but became dominant in June in the US.Įp 164-3: Kojima medRxiv July 2021: In a systematic “workforce screening” follow-up of 5306 subjects between May 2020 and July 2021, 258 SARS-CoV-2 infections were observed. Hence vaccination provides an additional layer of protection over “infection-induced immunity”. Clearly, these data are from a period with no variants and no vaccination.Įp 164-1 B: A very similar conclusion was reached by Victoria Hall in Lancet, based on the SIREN study in seropositive versus negative HCW in England over the same period (up to Jan 2020): 84% lower risk of re-infection.Įp 164-2: Cavanaught MMWR Aug 2021: Case-control amongst almost 750 community residents in Kentucky with previous SARS-CoV-2 infection in 2020, who were re-infected in May-June 2021, the risk was 2.34 times higher in those who were NOT vaccinated versus those who were vaccinated. According to this huge ( over 4 million) population study, protection by “natural immunity” was over 80 % in those younger than 65, but only 47 % in those over 65. Episode 164 (Re) infection after previous infection and/or vaccinationĮp 164-1 A: Hanssen in Lancet May 2021 on protection against re-infection during 2020.