Vaccine effectiveness against SARS-CoV-2 infection or COVID-19 hospitalization with the Alpha, Delta, or Omicron SARS-CoV-2 variant: A nationwide Danish cohort study

BACKGROUND

The continued occurrence of more contagious Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variants and waning immunity over time require ongoing reevaluation of the vaccine effectiveness (VE). This study aimed to estimate the effectiveness in 2 age groups (12 to 59 and 60 years or above) of 2 or 3 vaccine doses (BNT162b2 mRNA or mRNA-1273) by time since vaccination against SARS-CoV-2 infection and Coronavirus Disease 2019 (COVID-19) hospitalization in an Alpha-, Delta-, or Omicron-dominated period.

METHODS AND FINDINGS

A Danish nationwide cohort study design was used to estimate VE against SARS-CoV-2 infection and COVID-19 hospitalization with the Alpha, Delta, or Omicron variant. Information was obtained from nationwide registries and linked using a unique personal identification number. The study included all previously uninfected residents in Denmark aged 12 years or above (18 years or above for the analysis of 3 doses) in the Alpha (February 20 to June 15, 2021), Delta (July 4 to November 20, 2021), and Omicron (December 21, 2021 to January 31, 2022) dominated periods. VE estimates including 95% confidence intervals (CIs) were calculated (1-hazard ratio∙100) using Cox proportional hazard regression models with underlying calendar time and adjustments for age, sex, comorbidity, and geographical region. Vaccination status was included as a time-varying exposure. In the oldest age group, VE against infection after 2 doses was 90.7% (95% CI: 88.2; 92.7) for the Alpha variant, 82.3% (95% CI: 75.5; 87.2) for the Delta variant, and 39.9% (95% CI: 26.3; 50.9) for the Omicron variant 14 to 30 days since vaccination. The VE waned over time and was 73.2% (Alpha, 95% CI: 57.1; 83.3), 50.0% (Delta, 95% CI: 46.7; 53.0), and 4.4% (Omicron, 95% CI: -0.1; 8.7) >120 days since vaccination. Higher estimates were observed after the third dose with VE estimates against infection of 86.1% (Delta, 95% CI: 83.3; 88.4) and 57.7% (Omicron, 95% CI: 55.9; 59.5) 14 to 30 days since vaccination. Among both age groups, VE against COVID-19 hospitalization 14 to 30 days since vaccination with 2 or 3 doses was 98.1% or above for the Alpha and Delta variants. Among both age groups, VE against COVID-19 hospitalization 14 to 30 days since vaccination with 2 or 3 doses was 95.5% or above for the Omicron variant. The main limitation of this study is the nonrandomized study design including potential differences between the unvaccinated (reference group) and vaccinated individuals.

CONCLUSIONS

Two vaccine doses provided high protection against SARS-CoV-2 infection and COVID-19 hospitalization with the Alpha and Delta variants with protection, notably against infection, waning over time. Two vaccine doses provided only limited and short-lived protection against SARS-CoV-2 infection with Omicron. However, the protection against COVID-19 hospitalization following Omicron SARS-CoV-2 infection was higher. The third vaccine dose substantially increased the level and duration of protection against infection with the Omicron variant and provided a high level of sustained protection against COVID-19 hospitalization among the +60-year-olds.

Molecular epidemiology of the SARS-CoV-2 variant Omicron BA.2 sub-lineage in Denmark, 29 November 2021 to 2 January 2022

Following emergence of the SARS-CoV-2 variant Omicron in November 2021, the dominant BA.1 sub-lineage was replaced by the BA.2 sub-lineage in Denmark. We analysed the first 2,623 BA.2 cases from 29 November 2021 to 2 January 2022. No epidemiological or clinical differences were found between individuals infected with BA.1 versus BA.2. Phylogenetic analyses showed a geographic east-to-west transmission of BA.2 from the Capital Region with clusters expanding after the Christmas holidays. Mutational analysis shows distinct differences between BA.1 and BA.2.

Epidemiological characterisation of the first 785 SARS-CoV-2 Omicron variant cases in Denmark, December 2021

By 9 December 2021, 785 SARS-CoV-2 Omicron variant cases have been identified in Denmark. Most cases were fully (76%) or booster-vaccinated (7.1%); 34 (4.3%) had a previous SARS-CoV-2 infection. The majority of cases with available information reported symptoms (509/666; 76%) and most were infected in Denmark (588/644; 91%). One in five cases cannot be linked to previous cases, indicating widespread community transmission. Nine cases have been hospitalised, one required intensive care and no deaths have been registered.

Electronic reporting of diagnostic laboratory test results from all healthcare sectors is a cornerstone of national preparedness and control of COVID-19 in Denmark

The COVID‐19 pandemic has led to an unprecedented demand for real‐time surveillance data in order to inform critical decision makers regarding the management of the pandemic. The aim of this review was to describe how the Danish national microbiology database, MiBa, served as a cornerstone for providing data to the real‐time surveillance system by linkage to other nationwide health registries. The surveillance system was established on an existing IT health infrastructure and a close network between clinical microbiologists, information technology experts, and public health officials. In 2020, testing capacity for SARS‐CoV‐2 was ramped up from none to over 10,000 weekly PCR tests per 100,000 population. The crude incidence data mirrored this increase in testing. Real‐time access to denominator data and patient registries enabled adjustments for fluctuations testing activity, providing robust data on crude SARS‐CoV‐2 incidence during the changing diagnostic and management strategies. The use of the same data for different purposes, for example, final laboratory reports, information to the public, contact tracing, public health, and science, has been a critical asset for the pandemic response. It has also raised issues concerning data protection and critical capacity of the underlying technical systems and key resources. However, even with these limitations, the setup has enabled decision makers to adopt timely interventions. The experiences from COVID‐19 may motivate a transformation from traditional indicator‐based public health surveillance to an all‐encompassing information system based on access to a comprehensive set of data sources, including diagnostic and reference microbiology.

High-grade cervical intraepithelial neoplasia in human papillomavirus self-sampling of screening non-attenders

BACKGROUND

Self-sampling for human papillomavirus (HPV) offered to women who do not participate in cervical cancer screening is an increasingly popular method to increase screening coverage. The rationale behind self-sampling is that unscreened women harbour a high proportion of undetected precancer lesions. Here, we compare the cervical intraepithelial neoplasia grade 2 or worse (⩾CIN2) detection rate between non-attenders who participated in self-sampling and women attending routine screening.

METHODS

A total of 23 632 women who were qualified as non-attenders in the Copenhagen Region were invited for HPV-based self-sampling. Of these, 4824 women returned a self-sample, and HPV-positive women were referred for cytology and HPV co-testing as follow-up. The entire cohort and a reference cohort (3347 routinely screened women) were followed for histopathology confirmed ⩾CIN2. Odds ratio (OR) and the relative positive predictive value of ⩾CIN2 detection between the two populations were estimated.

RESULTS

Women participating in self-sampling had a higher ⩾CIN2 detection than women undergoing routine cytology-based screening (OR=1.83, 95% CI: 1.21-2.77) and a similar detection as routinely screened women tested with cytology and HPV testing (OR=1.03, 95% CI: 0.75-1.40). The positive predictive value for ⩾CIN2 was higher in screening non-attenders than in routinely HPV- and cytology-screened screened women (36.5% vs 25.6%, respectively).

CONCLUSIONS

Self-sampling offered to non-attenders showed higher detection rates for ⩾CIN2 than routine cytology-based screening, and similar detection rates as HPV and cytology co-testing. This reinforces the importance of self-sampling for screening non-attenders in organised cervical cancer screening.

Concordant testing results between various human papillomavirus assays in primary cervical cancer screening: systematic review

OBJECTIVES

Human papillomavirus (HPV) assays are increasingly used for primary cervical screening and HPV-vaccination-effect monitoring. We undertook a systematic literature review to determine the concordance in positive test results (i.e. detection of HPV infections) between Hybrid Capture 2 (HC2) and other assays.

METHODS

We searched PubMed, Embase and Scopus for studies of primary screening with HC2 and one or more assays, with cross-tabulated testing results for the assays. Two authors applied inclusion criteria and three authors extracted data from included studies. For each inter-assay comparison, we calculated the concordance by comparing the number of concordant samples with the number of samples that tested positive on at least one assay.

RESULTS

Sixteen studies fulfilled inclusion criteria, comparing nine assays to HC2, and including 392 to 9451 patients each. The calculated concordance varied between 48% and 69% for HC2 and APTIMA, Cobas, Abbott RealTime, Cervista, GP5+/6+, CLART, BD HPV test, Amplicor and Linear Array, i.e. 31%-52% of all positive tests on any pair of compared assays were discordant. Although modest variation in the degree of concordance with HC2 was suggested for particular assays, the numbers of studies per assay were generally low. No pronounced systematic patterns were observed by study (e.g. liquid medium) or population characteristics.

CONCLUSIONS

The ten commercially available assays do not detect the same HPV infections. Even in the most favourable case, the two assays provided discordant test results in 31% of all detected infections.

Human papillomavirus self-sampling for screening nonattenders: Opt-in pilot implementation with electronic communication platforms

In organized cervical screening programs, typically 25% of the invited women do not attend. The Copenhagen Self‐sampling Initiative (CSi) aimed to gain experiences on participation among screening nonattenders in the Capital Region of Denmark. Here, we report on the effectiveness of different communication platforms used in the pilot with suggestions for strategies prior to a full‐implementation. Moreover, an innovative approach using self‐sampling brushes with unique radio frequency identification chips allowed for unprecedented levels patient identification safety. Nonattenders from the capital region of Denmark were identified via the organized national invitation module. Screening history was obtained via the nationwide pathology registry. Twenty‐four thousand women were invited, and as an alternative to the regular communication platforms (letter and phone), women could request a home test via a mobile‐friendly webpage. Instruction material and video‐animation in several languages were made available online. Chi‐square test was used to test differences. Out of all invited, 31.7% requested a home test, and 20% returned it to the laboratory. In addition, 10% were screened at the physician after receiving the invitation. Stratified by screening history, long‐term unscreened women were less likely to participate than intermittently screened women (28% vs. 16%, p < 0.001). Of all contacts received, 64% (63–65) came via letter, and 31% (95CI: 30–32%) via webpage/mobile‐app. Self‐sampling was well‐accepted among nonattenders. Adopting modern technology‐based platforms into the current organized screening program would serve as a convenient communication method between health authority and citizens, allowing easy access for the citizen and reducing the work load in administrating self‐sampling approaches.

What's new?

Our implementation study is the first to evaluate opt‐in self‐sampling for 24,000 screening nonattenders, which can be basis for future routine implementation. Women could respond through a variety of communication channels (regular mail, phone and custom‐made web/mobile‐app). Our study utilized self‐sampling brushes with a novel RFID‐chip for secure patient‐identification, eliminating inconveniences for the women to fill out forms on returning the brush and loss of brushes due to missing identification.

Hysterectomy and its impact on the calculated incidence of cervical cancer and screening coverage in Denmark

BACKGROUND

The incidence rates of cervical cancer and the coverage in cervical cancer screening are usually reported by including in the denominator all women from the general population. However, after hysterectomy women are not at risk anymore of developing cervical cancer. Therefore, it makes sense to determine the indicators also for the true at-risk populations. We described the frequency of total hysterectomy in Denmark and its impact on the calculated incidence of cervical cancer and the screening coverage.

MATERIAL AND METHODS

With data from five Danish population-based registries, the incidence rate of cervical cancer and the screening coverage for women aged 23-64 years on 31 December 2010 were calculated with and without adjustments for hysterectomies undertaken for reasons other than cervical cancer. They were calculated as the number of cases divided by 1) the total number of woman-years from the general population; and 2) the at-risk population after exclusion of post-hysterectomy woman-years. Cases were defined as women with cervical cancer (incidence), or as women screened in the recommended interval, with or without adjustment for hysterectomies (coverage).

RESULTS AND CONCLUSIONS

In 2010, the all-age prevalence of hysterectomy was estimated at 6%, and ≥ 16% at age ≥ 65. This translated into an overall 6% increase in the incidence rate of cervical cancer, from 12.8 (unadjusted) to 13.5 (adjusted) per 100,000 woman-years. The screening coverage increased from 76% (unadjusted) to 79% (adjusted). In Denmark, hysterectomies do not have a large overall impact on the calculated cancer incidence and screening coverage. Nevertheless, at ≥ 65 years adjusted rates would increase by almost 20% compared to unadjusted rates. This suggests that calculating disease risks per organ-years may have a role in understanding the true burden of the disease in a population at risk of developing that disease.

Condom use in prevention of Human Papillomavirus infections and cervical neoplasia: systematic review of longitudinal studies

OBJECTIVES

Based on cross-sectional studies, the data on protection from Human Papillomavirus (HPV) infections related to using male condoms appear inconsistent. Longitudinal studies are more informative for this purpose. We undertook a systematic review of longitudinal studies on the effectiveness of male condoms in preventing HPV infection and cervical neoplasia.

METHODS

We searched PubMed using MeSH terms for articles published until May 2013. Articles were included if they studied a change in non-immunocompromized women's cervical HPV infection or cervical lesion status along with the frequency of condom use.

RESULTS

In total, 384 abstracts were retrieved. Eight studies reported in 10 articles met the inclusion criteria for the final review. Four studies showed a statistically significantly protective effect of consistent condom use on HPV infection and on regression of cervical neoplasia. In the remaining four studies, a protective effect was also observed for these outcomes, although it was not statistically significant.

CONCLUSIONS

Consistent condom use appears to offer a relatively good protection from HPV infections and associated cervical neoplasia. Advice to use condoms might be used as an additional instrument to prevent unnecessary colposcopies and neoplasia treatments in cervical screening, and to reduce the risk of cervical cancer.