Results
Table 1 shows the basic characteristics of the participants. 457
patients recovered from acute phase of COVID-19 and 108 of them
presented at least one symptom. The proportion of female was larger in
“Any symptom” group than that in “No symptom” group. There was no
substantial difference between the two groups in terms of their age and
medical history. Crude comparison of VAS and QOL showed that “Any
symptom” group had lower VAS and QOL values than the “No symptom”
group did (VAS: 70 vs 85, QOL: 0.81 vs 1.0, respectively).
(Table 1)
Table 2 describes the characteristics of the data after propensity score
matching. 91 pairs included in the matched data and 17 of “Any
symptom” group were discarded. Adjusted comparison of VAS and QOL
showed a similar trend to the results of crude comparison. Both VAS and
QOL were lower in the “Any symptom” group (VAS: 70 vs 80, QOL: 0.81 vs
1.0, respectively).
(Table 2)
Table 3 describes the characteristics of “long-COVID” symptoms. We
defined “long-COVID” as the status in which any symptoms attributed to
SARS-nCoV-2 infection lasting more than four weeks in the present study.
201 of 457 (44.0%) participants reported at least one symptom after
four weeks have passed since their symptom onset due to COVID-19. The
most common symptom of long-COVID was general fatigue. 58 of 457
(12.7%) participants have had general fatigue longer than four weeks.
The second most common symptom was alopecia. 55 of 457 (12.0%)
participants have experienced hair loss worse than usual.
(Table 3)
Figure 1 and 2 show a violin plot of VAS and QOL value, respectively.
The “Any symptom” group showed greater variance in both indicators.
(Figure 1)
(Figure 2)
Discussion
The present study demonstrated that the phenomenon we called
“long-COVID” can impair the HRQOL substantially. This would be another
important aspect of COVID-19 to consider because it implies a heavier
disease burden to us than other influenza like illnesses (ILIs) do, not
only due to its severity but also the characteristics of its chronic
phase. In the first place, COVID-19 showed higher case-fatality than
other ILIs.22–24 Additionally, it might cause a
substantial burden through accumulated mild disease only.
Furthermore, the frequency and the duration of symptoms due to
“long-COVID” are also noteworthy. Our results showed that nearly half
of the patients who recovered from acute COVID-19 (201/457) experienced
any symptoms lasting more than four weeks. As for patients who required
supplementary oxygen support, 32 out of 70 (45.7%) presented any
symptoms longer than four weeks. The precise duration of such symptoms
was not obvious because more than 100 participants reported that their
symptoms were still ongoing, nevertheless, we can say that the symptoms
attributed to “long-COVID” often continue several months. Albeit the
HRQOL value of the participants who have any “long-COVID” symptoms was
higher than that of the acute phase of other ILIs reported by a previous
study in Japan (0.81 vs 0.66, respectively)25, QOL
lost attributed to “long-COVID” should be greater than that due to the
acute phase of other ILIs because of its duration.
These results suggest that prevention is more important in COVID-19
countermeasures than other ILIs because effective treatment of
“long-COVID” is not clearly established yet.6,26Although there is no doubt that vaccination against SARS-CoV-2 will
reduce the risk of fatal and severe COVID-19,27–29its effectiveness against “long-COVID” is not demonstrated yet. This
may provide an additional incentive to prevent SARS-CoV-2 infection even
in the absence of known risk factors of severe illness.
There are several limitations in our study. First, our results are based
on the questionnaire survey then there are some recall biases in
participants’ responses. . Similarly, the potential participants were
enrolled from the visitors of outpatient department at the national
center hospital of infectious diseases in Japan, then the study
population might be influenced by selection biases. In addition, we
could not take “new variants” into consideration. The difference in
severity, infectiousness, and so forth between such new variants and old
ones were already reported,30–32 however, there is no
solid evidence about the frequency and the severity of “long-COVID”
symptoms in new variants. This should be the subject of future study.
In addition, we should be careful about the representativeness of the
data when we interpret the results because our survey includes a
comparatively small number of participants from Japan. However, the
response rate of our survey was extremely high (86.2%), and
non-response bias may therefore be limited. Furthermore, we compared VAS
and EQ-5D-3L values after adjusting participants’ background by
propensity score matching.
In conclusion, what we call “long-COVID” brings us substantial disease
burden in addition to the burden attributed to the acute phase of
COVID-19. This additional burden makes the whole disease burden of
COVID-19 heavier, making prevention strategies all the more important.
The influence of vaccination and variants on “long-COVID” should be
examined in the near future.