Analysis of related factors of plasma antibody levels in patients with severe and critical COVID-19 | Scientific Reports – Nature.com

With the virulence of SARS-CoV-2 had gradually diminished, China declared the end of its containment measures at the end of 2022. Owing to stringent domestic controls, there had been no widespread infections nationwide in China. Following the removal of relevant containment measures, numerous individuals infected with the current circulating strain emerged. Due to its weakened virulence, the majority of infected individuals experienced mild symptoms and could recover within one to two weeks after infection, but for older infected people, they might develop severe or critical illness. In this study, we found the plasma antibody level of the severe/critical group was significantly lower than that of the mild group. We thought this difference may be caused by the age of the participants and found there was indeed an association between plasma antibody levels and age in SARS-CoV-2 infectors. Previous reports suggest that older patients exhibit a reduced humoral immune response to vaccination, lower peak antibody titers, and a more rapid decline compared to younger patients8,9,10,11. Clemens A. Schmitt et al.6 reported COVID-19 brought bigger influence in the elderly based on cellular senescence. Furthermore, Parker et al.'s investigation revealed that individuals aged 4160years exhibited higher plasma antibody levels than other age groups12. Our finding was consistent with these reported studies. It was a negative correlation between age and plasma antibody levels in our severe/critical group. That means in severe and critical patients, older age is associated with an increased risk. Besides, age was positive correlated with antibody levels in the mild group in this study. Combining the results of the two groups, there may be an age interval where the correlation between age and antibody levels changes from positive to negative as patients age.

Strong epidemiological evidence exists that sex is an important biologic variable in immunity7. Some data demonstrate female immune system may generate stronger antibody responses13,14,15,16. Whether gender differences in the humoral immune response occur in COVID-19 remains unanswered. In our study, it seemed that plasma antibody levels were not associated with gender. But it could be observed from Table1 that the proportion of female patients was lower than that of male patients. More studies with larger sample sizes are needed to explore this association.

In addition to the factors above, we also found there existed a strong correlation between vaccination status and antibody levels in severe/critical patients. This suggests vaccination is meaningful for improving antibody levels and combating COVID-19.

There are several limitations to our study. These include the relatively small sample size, the lack of data on patients at younger ages, and the lack of clinical testing data. Besides, most patients in the mild group doesnt have basic disease, expect two individuals, which may influence the analysis results of this part. The host immune response is complex, and factors such as vaccine type, vaccination time, sample collection time, genetic factors, therapeutic intervention, and others may affect antibody levels. Most of the participants were vaccinated with inactivated virus vaccines (see Tables1, S1, and S2). Unfortunately, due to the difficulties in the actual information collection process, the data of vaccination type and vaccination time of all participants could not be obtained. The severe and critical patients in this study were older, the complications were common and the treatment situation was very complex and unavoidable. Thus, we regret that we were unable to deduct the impact of these factors. However, all the data were collected based on the reality. And the current study design allows for a preliminary assessment of the factors in the severe and critical COVID-19 patients. During the study period, there were no second infections among the included individuals. Further studies are needed to confirm our findings. We are also focusing on genetic factors and will conduct studies to discuss the correlation of antibody levels in patients with their immune profiles and genes.

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Analysis of related factors of plasma antibody levels in patients with severe and critical COVID-19 | Scientific Reports - Nature.com