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      Assessing the effectiveness of COVID-19 vaccines in Pakistan: a test-negative case-control study

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          Abstract

          Dear Editor, A recent publication in this journal by Hannawi et al. assessed a novel SARS-CoV-2 bivalent recombinant vaccine, SCTV01C, given as a booster to those who had previously received the primary series of an inactivated vaccine (1). The data showed that SCTV01C was well tolerated with a reactogenicity profile comparable to inactivated vaccines and induced substantial immune responses against Delta and Omicron variants (1). Inactivated vaccines are widely used in low-and middle-income countries (2). In Pakistan, Sinopharm (inactivated vaccine) was the first vaccine against COVID-19 to be introduced in February 2021. However, there is a paucity of vaccine effectiveness data from this region which undermines evidence-based decision-making. In addition, the protective effect of inactivated vaccines is considerably lower against emergent SARS-CoV-2 variants, signifying a need for booster doses (3). In Pakistan, eight different COVID-19 vaccines have been used since the launch of the government vaccination programme against covid 19, this provides an ideal setting for assessing the relative impact against symptomatic infection (4). We conducted a test-negative case-control study to assess the effectiveness of various COVID-19 vaccines, including mRNA, inactivated and viral vector vaccines, that were deployed in Pakistan. Adult residents of Karachi, Pakistan who tested for COVID-19 with RT-PCR at the Aga Khan University Hospital testing facility between June-September 2021 were contacted via phone calls. Participants who were symptomatic within a week prior to the test and provided verbal consent were enrolled in the study. Detailed information was collected on exposure, symptomatic history and vaccination status using a structured questionnaire. Individuals who were positive on PCR were classified as cases and those who tested negative were classified as controls. Effectiveness of different vaccines were calculated by comparing vaccination rates between cases and controls after adjusting for known confounders. In total, 1597 cases and 1590 controls were enrolled, of which 38·1% of the cases and 53·3% controls were fully vaccinated respectively. The mean duration of interval between last dose of vaccination and RT-PCR test among those who received a two-dose regimen was 27·3 days. Sinopharm was the most used vaccine (61·6%) followed by Sinovac (25·6%) and CanSinoBIO (8·9%). Only 33 individuals (2·3%) had received Sputnik-V, while the mRNA vaccines, Pfizer and Moderna, were each received by eight participants (0·5% each); Oxford/AstraZeneca was received by six (0·4%) and only two participants (0·1%) had received Janssen (Table 1 ). Table 1 Socio-demographic characteristics and vaccination status among cases and controls Table 1: Characteristics Total Cases Controls N=3187(%) N=1597(%) N=1590(%) p-value Age, years (mean ± SD) 38.5 ± 13.3 40.6 ± 14.2 36.4 ± 12.0 18 – 29 years 928 (29.1) 382 (23.9) 546 (34.3) <0.001 30 – 39 years 1045 (32.8) 513 (32.1) 532 (33.5) 40 – 49 years 544 (17.1) 283 (17.7) 261 (16.4) 50 – 59 years 358 (11.2) 207 (13.0) 151 (9.5) 60 – 69 years 230 (7.2) 149 (9.3) 81 (5.1) 70+ years 82 (2.6) 63 (3.9) 19 (1.2) Gender Female 1400 (43.9) 703 (44.0) 697 (43.8) 0.97 Male 1787 (56.1) 894 (56.0) 893 (56.2) Healthcare workers 626 (19.6) 211 (13.2) 415 (26.1) <0.001 Ethnicity n= 3183 n= 1595 n= 1588 Sindhi 352 (11) 156 (9.8) 196 (12.3) 0.06 Punjabi 244 (7.7) 123 (7.7) 121 (7.6) Pushto 79 (2.5) 39 (2.5) 40 (2.5) Balochi 50 (1.6) 30 (1.9) 20 (1.3) Urdu speaking 2089 (65.5) 1075 (67.4) 1014 (63.9) Others* 369 (11.7) 172 (10.8) 197 (12.4) Education status 14.1 ± 3.5 13.9 ± 3.7 14.3 ± 3.2 No formal education 60 (1.9) 41 (2.6) 19 (1.2) <0.001 Elementary (1 to 8 years) 107 (3.4) 57 (3.7) 50 (3.2) Secondary (9 to 12 years) 635 (20.3) 352 (22.5) 283 (18.1) Graduation (12 to 16 years) 1901 (60.8) 910 (58.3) 991 (63.2) Higher Education (17+ years) 426 (13.6) 202 (12.9) 224 (14.3) Previous COVID-19 infection 297 (9.3) 59 (3.7) 238 (15) <0.001 Use of facemask 2899 (91.0) 1442 (90.3) 1457 (91.6) 0.22 Type of facemask ⁎⁎ Surgical mask 2824 (88.6) 1407 (88.1) 1417 (89.1) 0.22 Cloth Mask 66 (2.1) 35 (2.2) 31 (2) Respirator 84 (2.6) 34 (2.1) 50 (3.1) Social Distancing 2261 (70.9) 1175 (73.6) 1086 (68.3) <0.001 Exposure to person with similar illness 684 (21.5) 414 (25.9) 270 (17.0) <0.001 Nature of contact Family member (lives with you) 326 (47.7) 215 (51.9) 111 (41.1) <0.001 Social contact 86 (12.6) 49 (11.8) 37 (13.7) Workplace 198 (29) 90 (21.7) 108 (40) Other 74 (10.8) 60 (14.5) 14 (5.2) Health status of participants at the time of Index test Isolating at home 3059 (96.0) 1565 (98.0) 1494 (94.1) <0.001 Hospitalized 41 (1.3) 32 (2.0) 9 (0.6) N/A 87 (2.7) 0 (0) 85 (5.4) Pregnant 60 (4.6) 27 (3.8) 33 (4.7) Concurrent medical conditions 659 (20.7) 395 (24.7) 264 (16.6) <0.001 Cancer 26 (3.9) 18 (4.6) 8 (3.0) 0.003 Diabetes 261 (39.6) 171 (43.3) 90 (34.1) Immunosuppression 17 (2.6) 11 (2.8) 6 (2.3) Cardiovascular 334 (50.7) 221 (55.9) 116 (43.9) Respiratory disorders 75 (11.4) 37 (9.4) 39 (14.8) Others⁎⁎⁎ 177 (26.9) 100 (25.3) 76 (28.8) Vaccination status ᵻ Non-vaccinated 1732 (54.3) 989 (61.9) 743 (46.7) <0.001 Vaccinated 1455 (45.7) 608 (38.1) 847 (53.3) Vaccination category ᵻᵻ Non-vaccinated 1164 (36.5) 670 (42.0) 494 (31.1) <0.001 Partially vaccinated 568 (17.8) 319 (20.0) 249 (15.7) Fully vaccinated 1455 (45.7) 608 (38.1) 847 (53.3) Type of vaccine administered ᵻᵻᵻ n=1455 n=608 n=847 RNA 16 (1.1) 5 (0.8) 11 (1.3) 0.18 Inactivated 1269 (87.2) 537 (88.3) 732 (86.4) Vector 170 (11.7) 66 (10.9) 104 (12.3) Brand of vaccine administered n=1455 n=608 n=847 Pfizer-BioNTech 8 (0.5) 4 (0.7) 4 (0.5) 0.05 Moderna 8 (0.5) 1 (0.2) 7 (0.8) Sinopharm 896 (61.6) 387 (63.7) 509 (60.1) Sinovac 373 (25.6) 150 (24.7) 223 (26.3) Oxford/AstraZeneca 6 (0.4) 3 (0.5) 3 (0.4) Sputnik-V 33 (2.3) 12 (2.0) 21 (2.5) CanSinoBIO 129 (8.9) 51 (8.4) 78 (9.2) Janssen 2 (0.1) 0 (0) 2 (0.1) ⁎ Ethnic groups from other parts of Pakistan ⁎⁎ Use of more than one type of facemask ⁎⁎⁎ Includes: high cholesterol, thyroid problems, allergies, renal disorders, etc. ᵻ Vaccinated: one dose of any vaccine received before the index test ᵻᵻ Non-vaccinated: never received a vaccine dose or duration between first dose of two-dose vaccine, or one dose of a single-dose regimen and index test was less than 14 days. Partially vaccinated: received one dose of a two-dose vaccine at least 14 days before the index test and had either not received the second dose or less than 14 days had elapsed between the second dose and time of index test. Fully vaccinated: received second dose of a two-dose vaccine or one dose of a single-dose regimen 14 or more days before the index test ᵻᵻᵻ mRNA vaccines: Pfizer-BioNTech, Moderna; Inactivated vaccines: Sinopharm, Sinovac; Viral-vector vaccines: Oxford/AstraZeneca, Sputnik-V, CanSinoBIO, Janssen After adjusting for age, gender, healthcare worker status, past COVID-19 infection, use of non-pharmaceutical interventions, diabetes, and hypertension, it was found that two doses of mRNA vaccines conferred the greatest protection (VE: 67·4%; 95% CI: 1·8-89·2%), followed by Sputnik-V (VE: 58·5%; 95% CI: 12·8-80·2%), Sinovac (49·3%; 95% CI: 34·8-60·6%) and Sinopharm (VE: 33·8%; 95% CI: 18·6, 46·1%) (Figure 1 ), while a single shot of CanSinoBIO was 47·9% effective in preventing symptomatic COVID-19. Among the partially vaccinated participants, VE estimates were lower, 29·8% for the mRNA vaccines, and 31·8% for Oxford/AstraZeneca. One dose of inactivated vaccines was ineffective in providing protection against symptomatic COVID-19 infection (Figure 1). Figure 1 Graph showing VE (95% CI) among fully vaccinated participants Figure 1: We found that two doses of inactivated vaccines had lower effectiveness against symptomatic disease (between 34% and 48%) compared with 2 doses of the mRNA vaccine (67%) during the period when the delta variant was in circulation. Overall, these estimates are lower than previous clinical trials (5). This could be because the vaccines may have become less effective as a result of emerging variants. We report a widespread use of two inactivated vaccines, Sinopharm and Sinovac, among the study population. We found that a two-dose schedule of Sinovac was around 47% effective at preventing symptomatic infection due to the Delta variant. This is consistent with previous estimates, including a recently published study from Jiangsu, China, which showed the vaccine to be 51% effective against symptomatic infection by the Delta variant (6). A similar estimate (46.8%) was reported for the Sinovac vaccine against the earlier variants in a test-negative case control study from Brazil 24 (7), while VE for Sinovac was estimated to be of 67% against symptomatic infection from a cohort study in Chile (2). Decline in the effectiveness of different COVID-19 vaccines against later variants has been reported from other studies as well (8). Bernal et al. reported effectiveness of two doses of Pfizer-BioNTech vaccine to be 93·7% and 88% against the alpha and Delta variants respectively, while Oxford-AstraZeneca vaccine was 74·5% against the alpha variant but 67% against the Delta variant (9). Nasreen et al. reported a similar decline of the effectiveness of the mRNA vaccines against the Delta variant in Ontario (10). Our study had a few limitations. Documentary verification of the vaccine status was not available as data were collected through phone calls which could have led to misclassification. We tried minimizing this bias by scheduling follow-up calls so that participants could verify their vaccination date using their vaccine card or certificate. The study participants may not be an ideal representative of the target population as certain groups were excluded based on the presence of risk factors. We had access to one of the largest testing facilities in the city and were able to assess the effectiveness across a range of vaccines against the Delta variant. The test negative study design controlled for differences in health-seeking behaviors and validity of the diagnostic tests, as all participants were tested at the same place. In addition, investigator bias was minimized as the lab personnel were blinded to both clinical presentation and vaccination status of the participants. In conclusion, inactivated COVID-19 vaccines were moderately effective against symptomatic infection in the adult Pakistani population. The mRNA vaccines had higher effectiveness comparable to that observed in other parts of the world. Our findings support a universal evaluation of all vaccines and consideration of additional doses for those who received inactivated vaccines. As countries implement or consider additional vaccine doses in various risk groups, there may be a need for additional booster doses among those who initially received the inactivated vaccines. Ethical statement Written consent was obtained from the study participants before their enrollment. Author contributions IN, SO, FJ, NA, AM, and IY conceptualized and designed the study. NA, AM, KL, and MM worked on developing the methodology. SO, IN, and FJ supervised the research. NA, KL, ZH, and UK were responsible for project administration. ZH and UK contributed to the availability of resources. NA, KL, AMY and MC were involved in the investigation process and curated and verified the data. NA, AM, AMY, MC, FK, and FQ performed the formal analysis. NA wrote the original draft and IN, FJ, SS, SO, AM, NA, and IY reviewed and edited it. NA and AM directly accessed and verified the underlying data reported in the manuscript. All authors confirm that they had full access to all the data in the study and accept responsibility to submit for publication. Data availability Deidentified data and data dictionary will be made available by the corresponding author upon request. Declaration of Competing Interest The authors declare no competing interests.

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          Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant

          Background The B.1.617.2 (delta) variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (Covid-19), has contributed to a surge in cases in India and has now been detected across the globe, including a notable increase in cases in the United Kingdom. The effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against this variant has been unclear. Methods We used a test-negative case–control design to estimate the effectiveness of vaccination against symptomatic disease caused by the delta variant or the predominant strain (B.1.1.7, or alpha variant) over the period that the delta variant began circulating. Variants were identified with the use of sequencing and on the basis of the spike ( S ) gene status. Data on all symptomatic sequenced cases of Covid-19 in England were used to estimate the proportion of cases with either variant according to the patients’ vaccination status. Results Effectiveness after one dose of vaccine (BNT162b2 or ChAdOx1 nCoV-19) was notably lower among persons with the delta variant (30.7%; 95% confidence interval [CI], 25.2 to 35.7) than among those with the alpha variant (48.7%; 95% CI, 45.5 to 51.7); the results were similar for both vaccines. With the BNT162b2 vaccine, the effectiveness of two doses was 93.7% (95% CI, 91.6 to 95.3) among persons with the alpha variant and 88.0% (95% CI, 85.3 to 90.1) among those with the delta variant. With the ChAdOx1 nCoV-19 vaccine, the effectiveness of two doses was 74.5% (95% CI, 68.4 to 79.4) among persons with the alpha variant and 67.0% (95% CI, 61.3 to 71.8) among those with the delta variant. Conclusions Only modest differences in vaccine effectiveness were noted with the delta variant as compared with the alpha variant after the receipt of two vaccine doses. Absolute differences in vaccine effectiveness were more marked after the receipt of the first dose. This finding would support efforts to maximize vaccine uptake with two doses among vulnerable populations. (Funded by Public Health England.)
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            Effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines on covid-19 related symptoms, hospital admissions, and mortality in older adults in England: test negative case-control study

            Objective To estimate the real world effectiveness of the Pfizer-BioNTech BNT162b2 and Oxford-AstraZeneca ChAdOx1-S vaccines against confirmed covid-19 symptoms (including the UK variant of concern B.1.1.7), admissions to hospital, and deaths. Design Test negative case-control study. Setting Community testing for covid-19 in England. Participants 156 930 adults aged 70 years and older who reported symptoms of covid-19 between 8 December 2020 and 19 February 2021 and were successfully linked to vaccination data in the National Immunisation Management System. Interventions Vaccination with BNT162b2 or ChAdOx1-S. Main outcome measures Primary outcomes were polymerase chain reaction confirmed symptomatic SARS-CoV-2 infections, admissions to hospital for covid-19, and deaths with covid-19. Results Participants aged 80 years and older vaccinated with BNT162b2 before 4 January 2021 had a higher odds of testing positive for covid-19 in the first nine days after vaccination (odds ratio up to 1.48, 95% confidence interval 1.23 to 1.77), indicating that those initially targeted had a higher underlying risk of infection. Vaccine effectiveness was therefore compared with the baseline post-vaccination period. Vaccine effects were noted 10 to 13 days after vaccination, reaching a vaccine effectiveness of 70% (95% confidence interval 59% to 78%), then plateauing. From 14 days after the second dose a vaccination effectiveness of 89% (85% to 93%) was found compared with the increased baseline risk. Participants aged 70 years and older vaccinated from 4 January (when ChAdOx1-S delivery commenced) had a similar underlying risk of covid-19 to unvaccinated individuals. With BNT162b2, vaccine effectiveness reached 61% (51% to 69%) from 28 to 34 days after vaccination, then plateaued. With ChAdOx1-S, effects were seen from 14 to 20 days after vaccination, reaching an effectiveness of 60% (41% to 73%) from 28 to 34 days, increasing to 73% (27% to 90%) from day 35 onwards. On top of the protection against symptomatic disease, a further 43% (33% to 52%) reduced risk of emergency hospital admission and 51% (37% to 62%) reduced risk of death was observed in those who had received one dose of BNT162b2. Participants who had received one dose of ChAdOx1-S had a further 37% (3% to 59%) reduced risk of emergency hospital admission. Follow-up was insufficient to assess the effect of ChAdOx1-S on mortality. Combined with the effect against symptomatic disease, a single dose of either vaccine was about 80% effective at preventing admission to hospital with covid-19 and a single dose of BNT162b2 was 85% effective at preventing death with covid-19. Conclusion Vaccination with either one dose of BNT162b2 or ChAdOx1-S was associated with a significant reduction in symptomatic covid-19 in older adults, and with further protection against severe disease. Both vaccines showed similar effects. Protection was maintained for the duration of follow-up (>6 weeks). A second dose of BNT162b2 was associated with further protection against symptomatic disease. A clear effect of the vaccines against the B.1.1.7 variant was found.
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              Effectiveness of an Inactivated SARS-CoV-2 Vaccine in Chile

              Background Mass vaccination campaigns to prevent coronavirus disease 2019 (Covid-19) are occurring in many countries; estimates of vaccine effectiveness are urgently needed to support decision making. A countrywide mass vaccination campaign with the use of an inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine (CoronaVac) was conducted in Chile starting on February 2, 2021. Methods We used a prospective national cohort, including participants 16 years of age or older who were affiliated with the public national health care system, to assess the effectiveness of the inactivated SARS-CoV-2 vaccine with regard to preventing Covid-19 and related hospitalization, admission to the intensive care unit (ICU), and death. We estimated hazard ratios using the extension of the Cox proportional-hazards model, accounting for time-varying vaccination status. We estimated the change in the hazard ratio associated with partial immunization (≥14 days after receipt of the first dose and before receipt of the second dose) and full immunization (≥14 days after receipt of the second dose). Vaccine effectiveness was estimated with adjustment for individual demographic and clinical characteristics. Results The study was conducted from February 2 through May 1, 2021, and the cohort included approximately 10.2 million persons. Among persons who were fully immunized, the adjusted vaccine effectiveness was 65.9% (95% confidence interval [CI], 65.2 to 66.6) for the prevention of Covid-19 and 87.5% (95% CI, 86.7 to 88.2) for the prevention of hospitalization, 90.3% (95% CI, 89.1 to 91.4) for the prevention of ICU admission, and 86.3% (95% CI, 84.5 to 87.9) for the prevention of Covid-19–related death. Conclusions Our results suggest that the inactivated SARS-CoV-2 vaccine effectively prevented Covid-19, including severe disease and death, a finding that is consistent with results of phase 2 trials of the vaccine. (Funded by Agencia Nacional de Investigación y Desarrollo and others.)
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                Author and article information

                Journal
                J Infect
                J Infect
                The Journal of Infection
                Published by Elsevier Ltd on behalf of The British Infection Association.
                0163-4453
                1532-2742
                25 January 2023
                25 January 2023
                Affiliations
                [1 ]The Aga Khan University, Karachi, Pakistan
                [2 ]Yale Institute of Global Health, New Haven, CT, USA
                [3 ]Yale School of Medicine, New Haven, CT, USA
                [4 ]Yale School of Public Health, New Haven, CT, USA
                [5 ]Yale School of Nursing, Orange, CT, USA
                Author notes
                [* ]Corresponding Author: Muhammad Imran Nisar, National Stadium Road, Aga Khan University Hospital, Karachi, Sindh
                Article
                S0163-4453(23)00021-X
                10.1016/j.jinf.2023.01.016
                9876011
                36708775
                ffa6766d-2111-4766-8366-cbf40086b3f9
                © 2023 Published by Elsevier Ltd on behalf of The British Infection Association.

                Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

                History
                : 12 January 2023
                Categories
                Letter to the Editor
                Letter to the Editor

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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