key: cord-0295404-oxa7670q
authors: Simwanza, J.; Hines, J. Z.; Sinyange, D.; Sinyange, N.; Mulenga, C.; Hanyinza, S.; Sakubita, P.; Langa, N.; Nowa, H.; Gardner, P.; Saasa, N.; Chipeta, G.; Simpungwe, J.; Malambo, W.; Hamainza, B.; Kapata, N.; Kapina, M.; Musonda, K.; Liwewe, M.; Mwale, C.; Fwoloshi, S.; Mulenga, L. B.; Agolory, S.; Mukonka, V.; Chilengi, R.
title: COVID-19 vaccine effectiveness during a prison outbreak when the Omicron was the dominant circulating variant, Zambia, December 2021
date: 2022-05-07
journal: nan
DOI: 10.1101/2022.05.06.22274701
sha: fc7c4058219117f225cbf6bc11c2d0c1e866c8be
doc_id: 295404
cord_uid: oxa7670q

Abstract: During a COVID-19 outbreak in a prison in Zambia from 14th to 19th December 2021, a case-control study was done to measure vaccine effectiveness (VE) against infection and symptomatic infection, when the Omicron variant was the dominant circulating variant. Among 382 participants, 74.1% were fully vaccinated and the median time since full vaccination was 54 days. There were no hospitalizations or deaths. COVID-19 VE against any SARS-CoV-2 infection was 62.8% and VE against symptomatic SARS-CoV-2 infection was 74.1%. COVID-19 vaccination helped protect incarcerated persons against SARS-CoV-2 infection during an outbreak while Omicron was the dominant variant in Zambia.

In total, 385 (50.2%) of the 767 incarcerated persons present during the outbreak were 1 0 7 reached for interview and 382 (49.8%) consented to being enrolled in the study. This article is a US Government work. It is not subject to copyright under 17 USC 105 and is also made available (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted May 7, 2022.

('booster') vaccine dose. The median time since receipt of a full primary vaccine series was 1 1 6 54 days (IQR: 28-85 days). 1 1 7

There were 180 (47.1%) COVID-19 positive incarcerated persons (i.e., cases) and 202 1 1 8 (52.9%) COVID-19 negative persons (i.e., controls). Among positive cases, 117 (65.0%) 1 1 9

were in fully vaccinated persons (i.e., breakthrough infections). Of the 16 (4.1%) persons 1 2 0 reporting prior confirmed COVID-19, 5 (29.4%) were positive during the outbreak (i.e., 1 2 1 reinfections Janssen vaccine against SARS-CoV-2 infection was 63.6% (95% CI: 33.6-80.5%) and 1 3 7 against symptomatic infection was 73.0% (95% CI: 41.6-87.7%). VE of AstraZeneca against 1 3 8 SARS-CoV-2 infection was 89.4% (95% CI: 59.5-97.8%) and against symptomatic infection 1 3 9

was 83.7% (95% CI: 60.8-93.6%). The sensitivity analysis excluding symptomatic controls 1 4 0 did not meaningfully change the VE estimates (VE against SARS-CoV-2 infection was 1 4 1 for use under a CC0 license.

This article is a US Government work. It is not subject to copyright under 17 USC 105 and is also made available (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. SARS-CoV-2 infection and symptomatic illness while Omicron was the dominant strain in the 1 5 0 country (1). These findings provide important evidence that might help increase COVID-19 1 5 1 vaccination in Zambia, where many more Zambians need to be vaccinated to reach the 1 5 2 African Union targets adopted by the country (10). 1 5 3

The SARS-CoV-2 Omicron variant contains numerous mutations to the spike protein which 1 5 4 may lead to immune evasion. VE estimates reported here are lower compared to prior 1 5 5 strains (11,12), and the high proportion of breakthrough infections in this outbreak supports 1 5 6 in theory the possibility of immune evading capability of Omicron. In this study, VE was 1 5 7 higher for symptomatic illness than any infection; VE for severe illness could not be 1 5 8 accessed because no persons were hospitalized or died during this outbreak although other 1 5 9 studies have demonstrated durability against this important outcome (13). Similarly, VE of a 1 6 0 booster dose could not be assessed because Zambia did not begin offering a booster dose 1 6 1 until January 2022. The relatively short time since vaccination might explain the relatively 1 6 2 higher effectiveness findings against Omicron (6,14,15), although there was a suggestion of 1 6 3 waning immunity when comparing the VE point estimates of participants fully vaccinated 1 6 4 over two months before the outbreak with those vaccinated within the past two months. Our 1 6 5 findings are encouraging considering alarm raised early in the Omicron wave about the 1 6 6 for use under a CC0 license.

This article is a US Government work. It is not subject to copyright under 17 USC 105 and is also made available (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. Notably, symptomology was mild among participants, which is consistent with reports from 1 6 9 other countries that are experiencing Omicron surges (9,17). Animal evidence suggests this 1 7 0 might be related to tropism of Omicron for upper respiratory epithelium relative to the lower 1 7 1 respiratory tract (18). This finding might also reflect the relatively younger age of persons in 1 7 2 this outbreak. The role of pre-existing immunity in Zambia from natural infection remains 1 7 3 uncertain and serosurveys would be useful to understand to what proportion of people in 1 7 4

Zambia have been infected with SARS-CoV-2. 1 7 5

This study had several limitations. All cases were confirmed with RDTs, which have lower 1 7 6 sensitivity than PCR tests (19). Additionally, beyond initial test results, serial testing was not 1 7 7 available meaning some controls might have been in their incubation period at the time of 1 7 8 testing and therefore misclassified. Omicron was not confirmed by genomic sequencing in 1 7 9 this outbreak, so the outbreak could have been from another strain; however, Omicron was This article is a US Government work. It is not subject to copyright under 17 USC 105 and is also made available (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. of SARS-CoV-2 in six districts in Zambia in July, 2020: a cross-sectional cluster 2 8 2 sample survey. Lancet Glob Heal. 2021;(21):1-9. This article is a US Government work. It is not subject to copyright under 17 USC 105 and is also made available (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. This article is a US Government work. It is not subject to copyright under 17 USC 105 and is also made available (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. ≤ 13 days before testing. Full vaccination was defined having received the 1 st dose of a one-dose vaccine or 2 nd dose of a two-dose vaccine ≥ 14 days before COVID-19 testing. Persons who were vaccinated with their 1 st dose 0-13 days before testing were considered to have indeterminate vaccination status and excluded from analyses. IQR: interquartile range; NC: not calculated This article is a US Government work. It is not subject to copyright under 17 USC 105 and is also made available (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 

One person was partially vaccinated and 10 were indeterminate vaccination status (i.e., vaccinated with their 1 st dose 0-13 days before COVID-19 testing) CI: confidence interval for use under a CC0 license

Grey GE, Collie S, Garrett N, Goga A, Champion J, Zylstra M, et al. Vaccine 2 2 8 effectiveness against hospital admission in South African health care workers who 2 2 9 received a homologous booster of Ad26.COV2 during an Omicron COVID19 wave: 2 3 0Preliminary Results of the Sisonke 2 Study. medRxiv [Internet] . Available from: 2 3 1 https://www.medrxiv.org/content/10.1101/2021.12.28.21268436v1 2 3 2

Bekker L-G, Garrett N, Goga A, Fairall L, Reddy T, Yende-Zuma N, et al.