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Authors: Seow et al. 

Journal/ Pre-PrintmedXriv 

Key Words: Immunology, Antibodies 

Research Highlights 

  1. 95% of RT-PCR confirmed COVID-19 patients showed servoconversion and neutralizing antibody responses 8 days post onset of symptoms 

  1. Neutralizing antibody titres are shown to decline during the follow up period 


Sera of 65 RT-qPCR confirmed COVID-19 infected individuals were analysed up to 94 days post onset of symptoms (POS). Seroconversion was shown in more than 95% of cases with neutralizing antibody responses emerging after 8 days POS. Antibody titres were dependent upon disease severity, which however did not affect neutralizing antibody response (nAb) kinetics. Declining Ab titres were observed during the follow up period, with some individuals with low peak titre peaks approaching baseline after 50 days POS. In contrast, those with high peak nAb titres were observed to maintain fairly high antibody titres at the final timepoint tested.   

Impact for SARS-CoV2/COVID19 research efforts  

Understand the immune response to SARS-CoV2/COVID19  

Treatment of SARS-CoV2/COVID19 positive individuals 

Study Type 

  • In vitro study 

  • Patient Case study 

Strengths and limitations of the paper 

Novelty: Longitudinal analysis of antibody titres up to day 94 post onset of symptoms 

Standing in the field:Appears to confirm some previously reported finding about declining antibody levels in COVID-19 patients. However, other reports (Wajnberg et al. 2020) suggest antibody titres to be much more stable up to 3 months post infection 

Appropriate statistics:Yes (but not entirely sure) 

Viral model used:Sera of RT-PCR confirmed COVID-19 patients 

Translatability:The findings have important implications for protective memory against re-infection and the durability of vaccine protection 

Main limitations:  

  • An HIV-1 based pseudotype assay was used to asses neutralizing activity; it would have been interesting to compare those results to results obtained by other assays such as the plaque neutralization assay 

  • Not entirely sure if their correlation analysis used in Figure 1B or 2A is the correct way to analyse this kind of data 

  • It would have been interesting to analyse the kinetics for all the different severity cases also separately  

  • Authors claim declining titre levels, which appears to be true for most patients (however, I would assume this probably is also to be expected). While some show a quite significant decline, some other patients show a much less dramatic decline with some of them having fairly stable or even slightly increasing ab titres (Figure 2B and Figure 4). It would have been interesting to compare the decline to other virus infections where correlates of protection are better established (e.g. Influenza) to get a better idea of how ab titres change post infection 

  • Correlates for protection (i.e. the nAb titre required for long-term protection) are still unknown for COVID-19 so conclusions about long-term immunity cannot be drawn from the results of this preprint