Title: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts
SUMMARY: Background: Impact of the Delta variant and vaccination on SARS-CoV-2 transmission remains unclear. In Singapore, quarantine of all close contacts, including entry and exit PCR testing, provided the opportunity to determine risk of infection by the Delta variant compared to other variants,...
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Elsevier
2021
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oai:doaj.org-article:b0b4cfbeebbb47139c5046aa29f77d762021-11-04T04:42:10ZTitle: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts2666-606510.1016/j.lanwpc.2021.100299https://doaj.org/article/b0b4cfbeebbb47139c5046aa29f77d762021-12-01T00:00:00Zhttp://www.sciencedirect.com/science/article/pii/S266660652100208Xhttps://doaj.org/toc/2666-6065SUMMARY: Background: Impact of the Delta variant and vaccination on SARS-CoV-2 transmission remains unclear. In Singapore, quarantine of all close contacts, including entry and exit PCR testing, provided the opportunity to determine risk of infection by the Delta variant compared to other variants, vaccine efficacy against SARS-CoV-2 acquisition, symptomatic or severe COVID-19, and risk factors associated with SARS-CoV-2 acquisition and symptomatic disease. Methods: This retrospective cohort study included all close contacts between September 1, 2020 and May 31, 2021. Regardless of symptoms, all were quarantined for 14 days with entry and exit PCR testing. Household contacts were defined as individuals who shared a residence with a Covid-19 index case. Secondary attack rates among household close contacts of Delta variant-infected indexes and other variant-infected indexes were derived from prevalence of diagnosed cases among contacts. Relative risk ratios and bootstrapping at the cluster level was used to determine risk of infection by the Delta variant compared to other variants and vaccine efficacy against SARS-CoV-2 acquisition, symptomatic or severe COVID-19. Logistic regression using generalized estimating equations was used to determine risk factors associated with SARS-CoV-2 acquisition and symptomatic disease Findings: Of 1024 household contacts linked to 301 PCR-confirmed index cases, 753 (73.5%) were linked to Delta-infected indexes and 248 (24.2%) were exposed to indexes with other variants. Household secondary attack rate among unvaccinated Delta-exposed contacts was 25.8% (95% boostrap confidence interval [BCI] 20.6–31.5%) compared with 12.9% (95%BCI 7.0–20.0%) among other variant-exposed contacts. Unvaccinated Delta-exposed contacts were more likely to be infected than those exposed to other variants (Relative risk 2.01, 95%CI 1.24–3.84). Among Delta-exposed contacts, complete vaccination had a vaccine effectiveness of 56.4% (95%BCI 32.6–75.8%) against acquisition, 64.1% (95%BCI 37.8–85.4%) against symptomatic disease and 100% against severe disease. Among Delta-exposed contacts, vaccination status (adjusted odds ratio [aOR] 0.33, 95% robust confidence interval [RCI] 0.17–0.63) and older age of the index (aOR 1.20 per decade, 95%RCI 1.03–1.39) was associated with increased risk of SARS-CoV-2 acquisition by the contact. Vaccination status of the index was not associated with a statistically-significant difference for contact SARS-CoV-2 acquisition (aOR 0.73, 95%RCI 0.38–1.40). Interpretation: Increased risk of SARS-CoV-2 Delta acquisition compared with other variants was reduced with vaccination. Close-contacts of vaccinated Delta-infected indexes did not have statistically significant reduced risk of acquisition compared with unvaccinated Delta-infected indexes.Oon Tek NgVanessa KohCalvin J ChiewKalisvar MarimuthuNatascha May ThevasagayamTze Minn MakJoon Kiat ChuaShannen Si Hui OngYong Kai LimZannatul FerdousAlifa Khairunnisa bte JohariMark I-Cheng ChenSebastian Maurer-StrohLin CuiRaymond Tzer Pin LinKelvin Bryan TanAlex R CookProf. Yee-Sin LeoProf. Vernon JM LeeElsevierarticlePublic aspects of medicineRA1-1270ENThe Lancet Regional Health. Western Pacific, Vol 17, Iss , Pp 100299- (2021) |
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DOAJ |
| collection |
DOAJ |
| language |
EN |
| topic |
Public aspects of medicine RA1-1270 |
| spellingShingle |
Public aspects of medicine RA1-1270 Oon Tek Ng Vanessa Koh Calvin J Chiew Kalisvar Marimuthu Natascha May Thevasagayam Tze Minn Mak Joon Kiat Chua Shannen Si Hui Ong Yong Kai Lim Zannatul Ferdous Alifa Khairunnisa bte Johari Mark I-Cheng Chen Sebastian Maurer-Stroh Lin Cui Raymond Tzer Pin Lin Kelvin Bryan Tan Alex R Cook Prof. Yee-Sin Leo Prof. Vernon JM Lee Title: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts |
| description |
SUMMARY: Background: Impact of the Delta variant and vaccination on SARS-CoV-2 transmission remains unclear. In Singapore, quarantine of all close contacts, including entry and exit PCR testing, provided the opportunity to determine risk of infection by the Delta variant compared to other variants, vaccine efficacy against SARS-CoV-2 acquisition, symptomatic or severe COVID-19, and risk factors associated with SARS-CoV-2 acquisition and symptomatic disease. Methods: This retrospective cohort study included all close contacts between September 1, 2020 and May 31, 2021. Regardless of symptoms, all were quarantined for 14 days with entry and exit PCR testing. Household contacts were defined as individuals who shared a residence with a Covid-19 index case. Secondary attack rates among household close contacts of Delta variant-infected indexes and other variant-infected indexes were derived from prevalence of diagnosed cases among contacts. Relative risk ratios and bootstrapping at the cluster level was used to determine risk of infection by the Delta variant compared to other variants and vaccine efficacy against SARS-CoV-2 acquisition, symptomatic or severe COVID-19. Logistic regression using generalized estimating equations was used to determine risk factors associated with SARS-CoV-2 acquisition and symptomatic disease Findings: Of 1024 household contacts linked to 301 PCR-confirmed index cases, 753 (73.5%) were linked to Delta-infected indexes and 248 (24.2%) were exposed to indexes with other variants. Household secondary attack rate among unvaccinated Delta-exposed contacts was 25.8% (95% boostrap confidence interval [BCI] 20.6–31.5%) compared with 12.9% (95%BCI 7.0–20.0%) among other variant-exposed contacts. Unvaccinated Delta-exposed contacts were more likely to be infected than those exposed to other variants (Relative risk 2.01, 95%CI 1.24–3.84). Among Delta-exposed contacts, complete vaccination had a vaccine effectiveness of 56.4% (95%BCI 32.6–75.8%) against acquisition, 64.1% (95%BCI 37.8–85.4%) against symptomatic disease and 100% against severe disease. Among Delta-exposed contacts, vaccination status (adjusted odds ratio [aOR] 0.33, 95% robust confidence interval [RCI] 0.17–0.63) and older age of the index (aOR 1.20 per decade, 95%RCI 1.03–1.39) was associated with increased risk of SARS-CoV-2 acquisition by the contact. Vaccination status of the index was not associated with a statistically-significant difference for contact SARS-CoV-2 acquisition (aOR 0.73, 95%RCI 0.38–1.40). Interpretation: Increased risk of SARS-CoV-2 Delta acquisition compared with other variants was reduced with vaccination. Close-contacts of vaccinated Delta-infected indexes did not have statistically significant reduced risk of acquisition compared with unvaccinated Delta-infected indexes. |
| format |
article |
| author |
Oon Tek Ng Vanessa Koh Calvin J Chiew Kalisvar Marimuthu Natascha May Thevasagayam Tze Minn Mak Joon Kiat Chua Shannen Si Hui Ong Yong Kai Lim Zannatul Ferdous Alifa Khairunnisa bte Johari Mark I-Cheng Chen Sebastian Maurer-Stroh Lin Cui Raymond Tzer Pin Lin Kelvin Bryan Tan Alex R Cook Prof. Yee-Sin Leo Prof. Vernon JM Lee |
| author_facet |
Oon Tek Ng Vanessa Koh Calvin J Chiew Kalisvar Marimuthu Natascha May Thevasagayam Tze Minn Mak Joon Kiat Chua Shannen Si Hui Ong Yong Kai Lim Zannatul Ferdous Alifa Khairunnisa bte Johari Mark I-Cheng Chen Sebastian Maurer-Stroh Lin Cui Raymond Tzer Pin Lin Kelvin Bryan Tan Alex R Cook Prof. Yee-Sin Leo Prof. Vernon JM Lee |
| author_sort |
Oon Tek Ng |
| title |
Title: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts |
| title_short |
Title: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts |
| title_full |
Title: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts |
| title_fullStr |
Title: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts |
| title_full_unstemmed |
Title: Impact of Delta Variant and Vaccination on SARS-CoV-2 Secondary Attack Rate Among Household Close Contacts |
| title_sort |
title: impact of delta variant and vaccination on sars-cov-2 secondary attack rate among household close contacts |
| publisher |
Elsevier |
| publishDate |
2021 |
| url |
https://doaj.org/article/b0b4cfbeebbb47139c5046aa29f77d76 |
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