Use of Population-Based Studies to Monitor and Understand the COVID-19 pandemic in Norway
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Using population-based studies to understand the short and long-term effects of COVID-19 and vaccination on people's health, and for measuring immunity after infection and vaccination.
When the SARS-CoV-2 pandemic reached Norway in February 2020, there was an immediate need for knowledge on the spread of the virus in the population. Although data can be obtained from national health registers, these registers lack detailed information about COVID-19 symptoms, long-term sequelea, testing behavior, quarantine measures, vaccination, mild side effects, and general health. Additionally, blood samples and other biological samples are important in order to address immunity after infection and vaccination.
The use of four Population-Based cohort studies to understand COVID-19
We are utilizing four cohort studies, with participants whose ages ranged from 6 to 80 years at the start of the pandemic (birth years 1940 to 2014):
- The Norwegian Mother, Father, and Child Cohort Study (MoBa)
- The Norwegian Influenza Study (NorFlu)
- Senior Cohort
- Young Adult
The Norwegian Mother, Father, and Child Cohort Study (MoBa)
MoBa was planned in the 1990s and recruited approximately 280,000 individuals between 1999 and 2008, including pregnant women, their partners, and children. A biobank was established, and participants were followed with various questionnaires. MoBa has a rich biobank and significant amounts of information about participants' health, demographics, and life situations dating back up to 20 years. The main purpose is to find the causes of diseases.
The Norwegian Influenza Study (NorFlu)
NorFlu was established during the A/H1N1/09 (“swine flu”) pandemic in 2009 and consists of 4,500 women who were pregnant during the pandemic and their children (born in 2009/2010). The main purpose is to understand the short and long-term health consequences of influenza and vaccination during pregnancy. A biobank was also established, and questionnaires were sent out following the MoBa model. In 2014/2015, over 600 mothers and children were invited for clinical examination and blood sampling. NorFlu specifically focuses on studying immune responses after vaccination and infection. In addition to antibody analyses, immune cells have been collected since 2010 for analyses of cell-mediated immune responses.
The Senior Cohort
The Senior Cohort has approximately 5,000 participants and was established towards the end of 2020, just prior to the roll-out of the COVID-19 vaccines. The study was established to complement NorFlu and MoBa in terms of age, especially with regards to investigating humoral and cellular immune responses after vaccination.
Participants, aged 65-80 at the time of recruitment in 2020/2021 (born in 1940-1955) and living in Oslo, were randomly selected from the National Population Register. All participants receive regular questionnaires, and a subset of approximately 400 participants also donate blood samples, to examine immune responses to SARS-CoV-2. For a full cohort description, see Ravussin et al., Lancet Healthy Longevity 2023 (doi: 10.1016/S2666-7568(23)00055-7)
The Young Adult Cohort
The Young Adult cohort has approximately 12,000 participants and was established in early 2021. This study was also established to complement NorFlu and MoBa in terms of age. Participants, aged 18-30 year at the time of recruitment (born 1991-2003) and living in Oslo, were randomly selected from the National Population Register. All participants receive regular questionnaires, and a subset of approximately 140 participants also donate blood samples, for analysis of humoral and cellular immunity.
Using the existing cohort study MoBa and NorFlu to understand the COVID-19 prevalence and long-term consequences (Long-Covid)
During the beginning of the COVID-19 pandemic from March 2020- March 2022, participants in MoBa and NorFlu received bi-weekly electronic questionnaires on symptoms, testing, vaccination, side effects and general health. Since then, questionnaires are distributed every 2-4 times a year. This has provided a population-based picture of symptom prevalence, in addition to duration and severity of symptoms. Furthermore, it is important for investigating the prevalence of long-term symptoms, (Long-Covid), and vaccine side- effects.
Using the cohorts to understand vaccine effectiveness and potential side effects of vaccination
In order to guide vaccine policy, it is essential to estimate vaccine effectiveness in post-marketing studies. We have monitored vaccination status and the number of doses individuals have received, and the number of infections and severity of illness, both through self-reported questionnaire data and through the National Immunization Registry (SYSVAK) and Norwegian Surveillance System for Communicable Diseases (MSIS).
Further, we have investigated potential side effects after vaccination. Most side effects are not recorded in national registers, and the spontaneous reporting system only provides information about those who are vaccinated, making it challenging to establish a basis for comparison. The duration of side effects can also be recorded, at different time intervals. This is important for capturing neurological outcomes that may occur after a long latency period. Cohorts are suitable for understanding why some people experience severe side effects while others do not and for understanding why some experience exacerbation of chronic diseases.
Using the cohort studies to measure seroprevalence, immune responses and protection against the SARS-CoV-2
An important use of the cohort studies is measuring immune responses, both after infection and vaccination, in a subset of participants. From April-December 2020, blood samples were obtained from MoBa and NorFlu families to examine the prevalence of antibodies against the coronavirus in the population of Oslo, to measure the spread of the virus. We randomly sampled almost 10 000 participants. From 2021 and onwards we have obtained repeated and longitudinal samples from individuals from all 4 cohorts, and also isolated PBMCs for cellular analysis in the NorFlu, Senior and Young adult cohorts. DNA and plasma have also been stored.
Samples have been taken from before and after COVID-19 vaccination in the same individuals, to assess both humoral and cellular responses, in close collaboration with Oslo University Hospital, Ullevål (OUS). The results are important for evaluating the number of vaccine doses which are needed in different population groups and the time interval between vaccines.
Understanding how the COVID-19 pandemic has affected mental health
We have investigated the relationship between work situation and life satisfaction during the pandemic. Analyses have also been conducted on the effect of the pandemic on disparities in mental health.
