Prevalence of SARS-CoV-2 antibodies in Germany
Seroprevalence studies have proven their worth in estimating the size and direction of an outbreak of infectious diseases, especially the current pandemic of Coronavirus 2 (SARS-CoV-2) induced Coronavirus Disease 2019 (COVID-19). A new study published on the medRxiv * preprint server describes the prevalence of SARS-CoV-2 antibodies in five representative regions of Germany.
Seroprevalence is the number of people in a population who have tested positive for a specific disease using serological samples (blood serum).
The German estimates of the number of infections in the population are mainly based on the number of mandatory reported infections that come from the local health authorities. After the first case was reported in January 2020, the strategy initially focused on case studies, tracing contacts and locating sources of infection.
The polymerase chain reaction (PCR) screening for SARS-CoV-2 genetic material was carried out for certain groups, for example healthcare workers.
As a result, estimates of virus transmission ruled out asymptomatic or mild infections as they fail to achieve medical treatment. The current study attempts to use population-based data on immunoglobulin (Ig) G titers specific for the viral spike antigen to calculate the number of people exposed and the infection mortality rate for each age group.
This would help monitor how well various population-level interventions are working and how to prevent further increases in incidence and shape vaccination policies.
MuSPAD sampling time per location compared to reported cases Source @RKI in Germany, July 2020 – February 2021, data for rural area and city of Osnabrück and Freiburg aggregated.
The researchers found 30 studies from Germany and found that reported seroprevalence was mostly low, below 5%, and mostly through hotspots or group-specific screening. They only considered a single study, which was referred to as the Corona sub-study of the Rhineland study, as corresponding to their criteria. This study calculated a low seroprevalence below 1%, which would mean that Germany remains almost entirely susceptible to the virus.
The current study is based on MuSPAD data (Multilocal and Serial Prevalence Study of Antibodies against SARS-2 Coronavirus in Germany). MuSPAD is a multi-locality study created by the researchers to understand the community prevalence of SARS-CoV-2 and to enable comparisons with other European countries.
It looks at seroprevalence by region, time point, social and demographic data, and comorbidities. The researchers randomly tested over 13,000 and 6,000 adults in two test rounds in five German countries with the Spike S1-specific IgG ELISA (Enzyme-Linked Immunosorbent Assay). The first group of participants was tested twice to monitor changes in seroprevalence over time.
Approximately 40% of participants in both stages had no history of symptomatic COVID-19-like illness since February 2020. Approximately 10% were exposed to a confirmed case.
Around 20% had household members who had tested for the virus using PCR. Less than 20% had been tested themselves. In the second stage, the proportion in both categories was around a third. In one district, Reutlingen, 8% of household members were tested in the first phase, but 45% in the second.
Less than 1% and just over 2% of the first and second level participants had tested positive at any point in time.
Infection is underestimated
The seroprevalence was low until the end of 2020 as many cases were not reported. Seropositivity was almost four times higher in patients with two or more COVID-19-like symptoms, such as loss of smell, cough, shortness of breath, fever, or fatigue.
The seroprevalence for the first stage in June 2020 was 2.4% for Reutlingen; 1.5% for Freiburg; and 2.3% for Aachen. These values increased for Reutlingen in October 2020, level 2, to 2.9%; 2.5% for Freiburg; 5.4% for Aachen; and 1.3% for Osnabrück, 2.4% for Magdeburg, both from November to December 2020.
Based on these results, there were approximately 2.5 to 4.5 more cases than reported to health officials, known as the surveillance detection rate (SDR). This was lowest in people aged 80 and over, who had the highest seroprevalence. “Detected age-specific differences in SDRs should be taken into account when modeling and predicting COVID-19 morbidity.”
With the second wave (November 2020 to February 2021) another 2-5% of the population were infected.
They also found that with efficient isolation and contact tracing, the number of people quarantined to prevent infection was 8.2.
Infectious Mortality Risks
Estimates of death from infections fell between 0.2% and 2.4% and increased with age.
The likelihood of seroprevalence was 80% higher with lower education. Conversely, smoking was only associated with half the probability of being seropositive. However, there is much evidence that the disease is much more serious in people with lung damage from smoking.
This is the first closely followed population-level seroprevalence study of SARS-CoV-2 in several regions in Germany. The two rounds of sampling helped to track the seroprevalence fluctuations in these representative regions.
However, the seroprevalence could not be measured at all points at the same time, which meant that the antibody levels would have decreased more significantly in the last people tested. At the same time, the second wave began towards the end of the second test level, which is reflected in the test results.
What are the effects?
The five conclusions were:
The pooled seroprevalence of 1.3% indicates that the prevalence has not been adequately reported, with only 20 to 40% of cases reported in the first wave but 40 to 50% in the second wave.
The seroprevalence remained low in all regions until mid-December 2020. This was due to the declining first wave in most regions, but for Magdeburg to the beginning of the second wave.
The SDR is twice as high in the first wave for people aged 80 and over, and the difference is between 25% and 50% for different cities. Detecting older people more efficiently through notification should help improve forecasting and risk assessment models and thus design targeted preventive measures.
The low death rate from infections in Magdeburg is attributed to the researchers who recorded the first period of the second wave, when the study ended before the record of deaths was completed. For example, they comprised 15 deaths as of November 15, 2020, compared to nearly 50 as of the end of the year.
The study also shows that contact tracing was highly efficient and only 8 people had to be quarantined to prevent infection.
Finally, the risk of virus containment from restricted education has also been observed, likely because it is linked to lower socioeconomic status and job shifts, increasing barriers to self-isolation at home.
“We recommend that the forecasting measures use regional age-specific underreporting rates, if available, in order to predict severe disease progression and death in more detail. We also recommend targeting testing and tracking efforts specifically at the younger and middle adult populations, who appear to be the most underreported in our study. “
* Important NOTE
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice / health-related behavior, or be treated as established information.