Mucosal immunity and antibody anergy in COVID-exposed Covishield vaccinees

Knowledge is limited on mucosal immunity induction and longitudinal responses to vaccination against SARS-CoV2. Here, we determined serum/salivary antibodies and cytokines after three Covishield vaccine doses. Sera from 205 healthcare workers (HCWs) one-month after first- dose; one-, three- and six-months after second-dose; paired sera and stimulated whole mouth fluid (SWMF) from 10 HCWs one-, three- and six-months after third-dose were tested for anti- spike SARS-CoV2 antibodies by ECLIA and for cytokines by ELISA/cytokine bead arrays. One-month after second-dose, antibodies had increased significantly (6-fold) in COVID-naive group, but declined (1.5-fold) in those previously exposed to COVID. At one-month after first- dose, IL-10 levels were statistically higher in the previously COVID-exposed group compared to COVID-naive group (p<0.02). Breakthrough infections were 44% in COVID-naive group, while re-infections were 27% in COVID-exposed group (p<0.02). Proinflammatory cytokines-IL- 17/IL-21 at one-month after first- and second-doses, and memory cytokines-IL-7/IL-15 at three- and six-months after second-dose were minimal. Antibodies spiked at one-month after third- dose and declined by three- and six-months after third-dose similar to post-second-dose. Paired sera and SWMF at one- and six-months after third-dose lacked adaptive immunity cytokine expression. Innate immunity cytokines (MIG, MCP-1, IL-8, TNF-, IL-6, IL-1{beta}) showed a declining trend in serum, but were sustained in SWMF. Thus, our findings suggest that first-dose acts as an antibody boost, while second-dose induces antibody anergy in the previously COVID- exposed group. Rapidly declining antibodies and minimal T cell cytokines raises concerns over their durability in subsequent virus exposures. Sustained innate cytokines emanating from the oral mucosa warrant further in-depth explorations.

Povidone iodine, hydrogen peroxide and chlorhexidine mouthwashes reduce SARS-CoV2 burden in whole mouth fluid and respiratory droplets

SARS-CoV2 is transmitted primarily through oral mouth secretions and respiratory droplets. Commercial mouthwashes, povidone iodine (PI), hydrogen peroxide (HP) and chlorhexidine (CHX) have been tested in cell culture and RT-PCR studies for their efficacy to reduce SARS-CoV2 burden. Here, we evaluated SARS-CoV2 burden in whole mouth fluid (WMF) and respiratory droplets (RD) samples before and after the use of PI, HP or CHX mouthwashes in hospitalized COVID-19 patients using RT-PCR and rapid antigen test (RAT). Thirty-six SARS-CoV2 RT-PCR-positive in-patients were randomly assigned to one of the four groups: 20 and 60 minutes after 1% w/v PI or 1.5% HP; 90 and 180 minutes after 1.5% HP or 0.2% w/v CHX. WMF and RD samples were collected concurrently at baseline and after the two different time points. RD (92%) showed a higher reduction in SARS-CoV2 burden than WMF samples (50%; p=0.008). SARS-CoV2 burden was statistically lower at both 20 minutes (p=0.02) and 60 minutes (p=0.03) with PI; at 20 minutes with HP (p=0.0001); and 90 minutes with CHX (p=0.04). The overall and individual mean logarithmic reductions in the WMF and RD samples were greater than 1.0 at 20, 60 and 90 minutes after PI, HP or CHX. RAT-positive patients at 90 minutes post-treatment (n=3) demonstrated a one log increase in virus copies. Among the three RAT-negative post-treatment patients, SARS-CoV2 burden declined by one log in two while the third patient had a slight increase in RNA copies. In conclusion, we have shown for the first time that the mouthwashes, PI, HP and CHX can reduce the SARS-CoV2 burden in the concurrently collected RD and WMF samples. RAT is more appropriate than RT-PCR to evaluate the efficacy of the mouthwashes.

Implications in the quantitation of SARS-CoV2 copies in concurrent nasopharyngeal swabs, whole mouth fluid and respiratory droplets

ImportanceThe nasopharyngeal swab (NPS) is considered the ideal diagnostic specimen for Covid-19, while WMF is recently promoted due to collection simplicity and importance in disease transmission. There is limited knowledge on the relative viral load in these samples - NPS, whole mouth fluid (WMF) and respiratory droplets (RD; another important source in transmission), on how the loads vary with disease severity and on how much virus is shed. ObjectiveTo quantify and compare SARS-CoV2 copies in the NPS, WMF and RD samples, and correlate with disease severity. DesignCross sectional study. SettingTertiary care multi-speciality hospital with limited resources in a low-to-middle income country. ParticipantsEighty suspected COVID-19 patients were recruited from the COVID-19 out-patient clinic and hospital isolation wards. InterventionConcurrent NPS, WMF and RD samples were collected from all the recruited patients and tested for SARS-CoV2 copies by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Main outcomes and measuresThe main outcome was COVID-19 measured by SARS-CoV2 quantitative RT-PCR in NPS samples. COVID-19 disease severity was determined according to NIH criteria. Virus shedding was defined as the presence of SARS-CoV2 copies in the WMF and RD samples. ResultsSARS-CoV2 was detected in 55/80 (69%) of the NPS samples. Of these 55, WMF and RD samples were positive in 44 (80%) and 17 (31%), respectively. The concordance of WMF with NPS was 84% (p=0.02). SARS-CoV2 copy numbers were comparable in the NPS (median: 8.74x10^5) and WMF (median: 3.07x10^4), but lower in RD samples (median: 3.60x10^2). Patients with mild disease had higher copies in the NPS (median: 3.46x10^6), while patients with severe disease had higher copies in the WMF (median: 1.34x10^6) and RD samples (median: 4.29x10^4). The 25-75% interquartile range of NPS SARS-CoV2 copies was significantly higher in the WMF (p=0.0001) and RD (p=0.01) positive patients. Conclusion and relevanceSARS-CoV2 copies are highest in NPS samples. WMF is a reliable surrogate sample for diagnosis. High copy numbers in the NPS imply initial virological phase and higher risk of virus shedding via WMF and RD. Key pointsO_ST_ABSQuestionC_ST_ABSHow the numbers of SARS-CoV2 copies in nasopharyngeal swab (NPS) samples might reflectvirus shedding from the whole upper aerodigestive tract and indicatedisease severity? FindingsIn this cross-sectional study involving 80 suspected COVID-19 patients, the data indicate higher SARS-CoV2 copies in NPS samples of patients with mild disease,and in the whole mouth fluid (WMF) and respiratory droplet (RD) samples of patients with severe disease. Patients with higher SARS-CoV2 copies in the NPS shed the virus in the WMF and RD samples at statistically higher levels. MeaningHigh SARS-CoV2 copies in NPS samples imply initial virological phase withhigh levels of shedding through both WMF and RD.

Detection of SARS-CoV2 antigen in human saliva may be a reliable tool for large scale screening

IntroductionSARS-CoV2, the aetiological agent of the current COVID-19 pandemic, has been detected in saliva and recently implicated in several oral diseases. Collection of nasopharyngeal swabs (NPS) and detection by reverse transcriptase-polymerase chain reaction (RT-PCR) requires medical / technical expertise. A reliable and easy to handle point-of-care (POC) test is highly desirable, especially to curb transmission. Therefore, in this study, we evaluated a commercially available POC rapid antigen test (RAT) for the detection of SARS-CoV2 antigens in the saliva of RT-PCR confirmed positive and negative patients. MethodsThirty saliva samples of 10 saliva RT-PCR negative and 20 saliva RT-PCR positive patients were tested by RAT. ResultsRAT was negative in 10/10 (100%) RT-PCR-negative samples; positive in 9/20 (45%) RT-PCR-positive samples; concordance was 63% (p=0.001). Patients with positive RAT had higher virus copies in their NPS samples compared to the RAT-negative patients. This difference was also statistically significant (p=0.01). ConclusionThus, the POC RAT may be used to detect SARS-CoV2 as a reliable tool for self-testing, large-scale population screening and emergency medical/dental screening. Patients negative by RAT should be confirmed by RT-PCR.