RESUMEN
The SARS-CoV-2 mRNA vaccine BNT162b2 (Pfizer-BioNTech) has become a game-changer in the COVID-19 crisis. Faster and wider coverage of vaccine supply is urgently needed, although vaccine supply is far from abundant in many countries and regions. There is no denying that Japan is vaccinating at a slower pace than in many other countries. At the end of April 2021, it had administered less than 2% of the population, according to the statistics website Our World in Data.1 Single-dose vaccination may be considered to induce an adequate antibody response in individuals with prior infection,2-5 which can lead to more effective vaccine distribution to people in serious need. However, multiple antibody responses in populations with various backgrounds, including prior COVID-19 infection, underlying diseases, and age, have not been investigated sufficiently. Due to the lack of antibody measurement data, antibody follow-up measurement recommendations have yet to be suggested. Accumulation of available data regarding quantitative antibody titer will lead to the establishment of personally customized schedules, including antibody follow-up, and will balance both faster delivery of vaccines and confirmation of effective vaccination.
RESUMEN
BackgroundA few studies on antibody testing have focused on asymptomatic or mild coronavirus disease 2019 (COVID-19) patients with low initial anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody responses. Anti-SARS-CoV-2 antibody-testing performance was evaluated using blood samples from asymptomatic or mild COVID-19 patients. MethodsBlood samples were collected from 143 COVID-19 patients during an outbreak on a cruise ship 3 weeks after diagnosis. Simultaneously, a second SARS-CoV-2 genetic test was performed. Samples stored before the COVID-19 pandemic were also used to evaluate the lateral flow immunochromatographic assay (LFA) and electrochemiluminescence immunoassay (ECLIA). Titers of anti-SARS-CoV-2 IgM and IgG antibodies against the nucleocapsid and spike proteins were measured using the enzyme-linked immunosorbent assay to compare false-negative-with positive-result samples. ResultsSensitivity, specificity, positive-predictive, and negative-predictive values of LFA-detected IgM antibodies were 0.231, 1.000, 1.000, and 0.613, respectively; those of LFA-detected IgG antibodies were 0.483, 0.989, 0.972, and 0.601, respectively; and those of ECLIA-detected total antibodies were 0.783, 1.000, 1.000, and 0.848, respectively. IgM-, IgG-, and total-antibody positivity rates in the patients with negative results from the second genetic testing were 22.9%, 47.6%, and 72.4%, respectively. All antibody titers, especially those of the IgG antibody against nucleocapsid protein, were significantly lower in blood samples with false-negative results than in those with positive results. ConclusionsThese findings suggest that anti-SARS-CoV-2 antibody testing has lower performance in asymptomatic or mild COVID-19 patients than required in the guidelines, and situations in which it is useful are limited.