Dynamics of neutralizing antibody responses to SARS-CoV-2 in patients with COVID-19: an observational study

Our understanding of the protective immunity,particularly the long-term dynamics of neutralizing antibody(NAbs)response to SARS-CoV-2,is currently limited.We enrolled a cohort of 545 COVID-19 patients from Hubei,China,who were followed up up to 7 months,and determined the dynamics of NAbs to SARS-CoV-2 by using a surrogate virus neutralization test(sVNT).In our validation study,sVNT IC50 titers and the neutralization rate measured at a single dilution(1:20)were well correlated with FRNT titers(r=0.85 and 0.84,respectively).The median time to seroconversion of NAbs was 5.5 days post onset of symptoms.The rate of positive sVNT was 52% in the first week,reached 100% in the third week,and remained above 97% till 6 months post onset.Quantitatively,NAbs peaked in the fourth week and only a quarter of patients had an estimated peak titer of>1000.NAbs declined with a half-time of 61 days(95%CI:49-80 days)within the first two months,and the decay deaccelerated to a half-time of 104 days(95%CI:86-130 days)afterward.The peak levels of NAbs were positively associated with severity of COVID-19 and age,while negatively associated with serum albumin levels.The observation that the low-moderate peak neutralizing activity and fast decay of NAbs in most naturally infected individuals called for caution in evaluating the feasibility of antibody-based therapy and vaccine durability.NAbs response positively correlated with disease severity,warning for the possibility of repeat infection in patients with mild COVID-19.

Personnel protection strategy for healthcare workers in Wuhan during the COVID-19 epidemic

Objective:To identify the effectiveness of a personnel protection strategy in protection of healthcare workers from SARS-CoV-2 infection.Design:During the COVID-19 pandemic,943 healthcare staff sent from Guangzhou to Wuhan to care for patients with suspected/confirmed COVID-19 received infection precaution training before their mission and were equipped with Level 2/3 personal protective equipment(PPE),in accordance with guidelines from the National Health Commission of China.We conducted a serological survey on the cumulative attack rate of SARS-CoV-2 among the healthcare workers sent to Wuhan and compared the seropositive rate to that in local healthcare workers from Wuhan and Jingzhou.Results:Serial tests for SARS-CoV-2 RNA and tests for SARS-CoV-2 immunoglobulin M and G after the 6-8 week mission revealed a zero cumulative attack rate.Among the local healthcare workers inWuhan and Jingzhou of Hubei Province,2.5%(113 out of 4495)and 0.32%(10 out of 3091)had RT-PCR confirmed COVID-19,respectively.The seropositivity for SARS-CoV-2 antibodies(IgG,IgM,or both IgG/IgM positive)was 3.4%(53 out of 1571)in local healthcare workers from Wuhan with Level 2/3 PPE working in isolation areas and 5.4%(126 out of 2336)in healthcare staff with Level 1 PPE working in non-isolation medical areas,respectively.Conclusions and relevance:Our study confirmed that adequate training/PPE can protect medical personnel against SARS-CoV-2.