Discussion
While our knowledge regarding the risk factors for reinfection and other
associated parameters are evolving, data points out the temporary
protectivity of anti SARS-CoV-2 antibodies6 and the
emergence of viral escape mutants as potential mechanisms for recurrent
cases7. Our case developed a reinfection with
SARS-CoV-2 after an initial episode of symptomatic disease and a 2-month
disease-free interval. The second episode was significantly milder
requiring no inpatient medical care but relatively different in
presentation from the initial episode. In a surveillance study at the
Oxford University Hospitals in the United Kingdom, Lumley et al.
measured anti-spike and anti-nucleocapsid IgG antibodies in 12,541
healthcare workers and followed them for a period of 31 weeks6. The authors found that out of 1,265 seropositive
cases, 88 had developed seroconversion during the follow-up period. On
the other hand, 223 seronegative subjects developed a positive PCR test
(1.09 per 10,000 days at risk) of whom 44.84% were asymptomatic and
51.6% were symptomatic. This was significantly different from the only
2 seropositive cases who became PCR-positive during the follow-up period
(0.13 per 10,000 days at risk). While in average the anti SARS-CoV-2
antibodies rendered an immunity against reinfection for a duration of
6-month, our case report along with others raise questions about the
generalizability of such a short-term protection4,5.
However, none of these case reports have monitored the evolution of
neutralizing antibodies against SARS-CoV-2 from the initial infection to
the time of reinfection.
A genomic analysis of SARS-CoV-2 obtained at two different times from a
25-year-old man from Washoe, Nevada revealed genetically significant
differences between the two species4. Unlike our
patient’s, the second episode was more severe in terms of clinical
symptomatology. Further case reports have also shown a declining
antibody titer to coincide with the reinfection of SARS-CoV-22,3,8. The case report from Hong Kong showed that an
initially mild infection with SARS-CoV-2 did not produce any effective
neutralizing antibody, which 5 months later resulted in reinfection with
the virus although completely asymptomatic 2. Another
case report from Netherlands showed a more severe presentation of
SARS-CoV-2 reinfection compared to the index episode3. Although the latter patient was immunocompromised
due to recent B-cell depleting chemotherapy for Waldenström’s
macroglobulinemia, an effective innate immune or T-cell response might
have acted as a savior. The same path can be imagined for the case
report from Hong Kong in whom no effective neutralizing antibody was
detected in either of the episodes. Unfortunately, our current
laboratory setting did not permit measuring anti SARS-CoV-2 serum
antibody titers from the index infection to the recurrence of COVID-19
nor did it allow the genomic analysis of the causative agents in these
two different episodes.
The time interval between the initial infection with SARS-CoV-2 and the
second episode has been variably reported in the literature3-5,8. While the duration of protectivity rendered by
anti-spike or anti-nucleocapsid IgG antibodies has been shown to be a
minimum of 6 months, a systematic review of the reported cases of
reinfection with SARS-CoV-2 has estimated this interval to be 35.4
days5. The review has also found that younger age and
a longer time to become PCR-negative is significantly associated with a
higher risk of reinfection with SARS-CoV-2 while a severe disease might
play a protective role.
Our case report supports the growing doubt about a lasting herd immunity
against SARS-CoV-2. Although our patient presented differently in the
second episode from the initial one, the clinical manifestation was less
severe clinically. The time from initial infection to the recurrent
episode was above the average reported in the literature. However, we
could not examine the evolution of neutralizing antibody over this
interval as the titer was not measured in our case. While the current
endeavors in global vaccination against SARS-CoV-2 is ongoing,
clinicians should stay alert about variation in individuals’ response to
the infection and the potential risk of reinfection despite receiving
the vaccine. This is especially important when we are reading the news
about the emerging variants of the virus, which seem to be more
contagious9.