Natural immunity

Past SARS-CoV-2 infection protection against re-infection: a systematic review and meta-analysis https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(22)02465-5/fulltext Group 1 Past SARS-CoV-2 infection Group 2 No past SARS-CoV-2 infection Effectiveness of past infection by outcome Infection Symptomatic disease Severe disease Findings High levels of protection from infection caused by Alpha, beta, and delta variants Lower levels of protection from infection caused by Omicron BA.1 variant Effectiveness against re-infection with the omicron BA.1 variant Protection against reinfection, 45·3% Protection against omicron BA.1 symptomatic reinfection, 44% Protection against severe disease if reinfected with BA.1 is 88.9% Protection from re-infection with ancestral strains Alpha and delta variants Declined over time 78·6% at 40 weeks Protection against re-infection with omicron BA.1 Declined more rapidly 36·1% at 40 weeks Protection against severe disease at 40 weeks if reinfected Remained high for all variants 90·2% for alpha and delta variants 88·9% for omicron BA.1 Data suggests that the level of protection afforded by previous infection is at least as high, if not higher than that provided by two-dose vaccination using high-quality mRNA vaccines As of June 1, 2022 COVID-19 pandemic had caused an estimated 17·2 million total deaths 6·88 million reported deaths 7·63 billion total infections and re-infections. Between 15th November 2021 and 1st June 2022 3·8 billion people 46% of the global population, have been infected by omicron and sublineages. Understanding needed for Predicting future potential disease burden Designing policies, travel, access to venues Informing choices, vaccines Estimate protection from past infection Systematically synthesise studies 65 studies from 19 countries By variant By time since infection Up to Sept 31, 2022