Therefore, how long an individual is protected from further SARS-CoV-2 infection after recovering from COVID-19, becomes an important research question during this prolonged pandemic. identified reinfection cases within 19 days by different PANGO Lineage SARS-CoV-2 15. Although, CDC considered symptomatic infection < 35 Ct-value with ≥ 45 days interval between two rRT-PCR tests as reinfection cases 14 Tang et al. Recently, the number of reinfection cases have been increasing globally 13. But, the concentration of neutralising antibodies is another factor to confer protection against SARS-CoV-2 reinfection 12. More than 95% of symptomatic cases develop antibodies within 14 days, and by day 30, 100% symptomatic and 45% asymptomatic cases become fully seroconverted 11.
Therefore, the protection against the new variants with pre-existing antibodies due to natural infection or vaccination becomes a global concern 8, 9, 10. However, even with high vaccine coverage, many countries face multiple waves with faster high altitude spread than the previous 1, 4, 5, 6, 7. Recent studies suggest that natural infections are protective against reinfection at least for 8–12 months 3 and vaccination confers strong resistance against variants of concern, including the Delta variant. Until July 2021, six additional COVID-19 vaccines (mRNA-1273, BNT162b2, Sputnik V,, BBIBP-CorV/Vero Cells, and CoronaVac) have been approved by the Govt. In Bangladesh, the COVID-19 vaccination started on 27 January 2021 with COVISHIELD™ (ChAdOx1 nCoV-19 Corona Virus Vaccines manufactured by Serum Institute of India Pvt Ltd). Many of these COVID-19 positive cases had reported previous experience with natural infection or vaccination. Although, reinfected individuals did not suffer severe disease, a remarkable proportion of naturally infected or vaccinated individuals were (re)-infected by the emerging variants.īangladesh observed the third wave of COVID-19 pandemic and faced a record upsurge during June–September 2021, fueled by the highly contagious Delta variant 1. Naturally infected populations were less likely to be reinfected by SARS-CoV-2 than the infection-naïve and vaccinated individuals. Genome sequences showed that genetically distinct SARS-CoV-2 strains were responsible for reinfections. The risk of infection among positive cohort was 80.2% lower than negative cohort (95% CI 72.6–85.7% p < 0.001). Hypertension and diabetes mellitus were found significantly higher among the hospitalised patients compared to out-patients risk ratio 1.3 and 1.6 respectively. Among hospitalized patients, 45.9% had severe to critical disease and 42.5% required oxygen support. The positive cohort included 750 positive patients (564 from baseline and 186 from negative cohort follow-up), of whom 27.6% were hospitalized and 2.5% died. From 19 March 2020 to 31 March 2021, 1644 (mean age, 38.4 years and 57% male) participants were enrolled where 1080 (65.7%) were tested negative and added to the negative cohort. Reinfection cases were confirmed by whole-genome sequencing. A cohort was designed among icddr,b staff registered for COVID-19 testing by real-time reverse transcriptase-polymerase chain reaction (rRT-PCR). We aimed to investigate the rate of SARS-CoV-2 infection and its clinical features among infection-naïve, infected, vaccinated, and post-infection-vaccinated individuals.
The protection against emerging SARS-CoV-2 variants by pre-existing antibodies elicited due to the current vaccination or natural infection is a global concern.
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