Apologies if the text formatting comes out staggered on mobile devices. I used pdftotext, should be fine on larger screens.
SARS-CoV-2 seroprevalence in COVID-19 hotspots
Severe acute respiratory syndrome coronavirus 2 range of 3·7% [both tests positive] to 6·2% [at least
(SARS-CoV-2) has surprised the world with its range of one test positive]), with urban areas around Madrid
disease manifestations, from asymptomatic infection exceeding 10% (eg, seroprevalence by immunoassay in
to critical illness leading to hospital admission and Cuenca of 13·6% [95% CI 10·2–17·8]). These differences
death.1,2 Due to the high proportion of asymptomatic in seroprevalence are also reflected in laboratory-
or mild infections (approximately 80%), data restricted confirmed COVID-19 cases, which were much higher
to laboratory-confirmed cases do not capture the in urban areas than in rural areas. Similar numbers
true extent of the spread or burden of the virus, or its were obtained across the 2766 participants in the
infection-fatality ratio.2 Therefore, serological detection Swiss study,7 with seroprevalence data from Geneva
of specific antibodies against SARS-CoV-2 can better reaching 10·8% (8·2–13·9) in early May. The rather
estimate the true number of infections. Due to co- low seroprevalence in COVID-19 hotspots in both
circulation of other human coronaviruses, serology for studies is in line with data from Wuhan, the epicentre
SARS-CoV-2 is not trivial. Antibody cross-reactivity with and presumed origin of the SARS-CoV-2 pandemic.
other human coronaviruses has been largely overcome Surprisingly, the study done in Wuhan approximately
by using selected viral antigens, and several commercial 4–8 weeks after the peak of infection reported a
assays are now available for SARS-CoV-2 serology. low seroprevalence of 3·8% (2·6–5·4) even in highly
However, despite high sensitivity and specificity, a exposed health-care workers, despite an overwhelmed
setting with a low pretest probability, such as current health-care system.4 None of the studies reported sex
population-based seroprevalence studies, warrants differences, and both the studies from Geneva and
careful validation of results.3 Extensive previous assay Spain reported lower seroprevalence in children than
validation in well characterised serum samples and in adults.6,7 Whether this reflects a lower susceptibility
confirmation of positive results are thus necessary of children to infection in general, or rather that the
to prevent false-positive findings from confounding studies were undertaken while schools and day-care
seroprevalence rates. centres were closed, remains to be elucidated.
The first SARS-CoV-2 seroprevalence studies from The key finding from these representative cohorts is
cohorts representing the general population have that most of the population appears to have remained
become available from COVID-19 hotspots such as unexposed to SARS-CoV-2, even in areas with
China, the USA, Switzerland, and Spain.4–8 In The Lancet, widespread virus circulation. These findings are further
Marina Pollán and colleagues6 and Silvia Stringhini and supported by the observation that even countries
colleagues7 separately report representative population- without strict lockdown measures have reported
based seroprevalence data from Spain and Switzerland similarly low seroprevalence—eg, Sweden, which
collected from April to early May this year. Studies reported a prevalence of 7·3% at the end of April—
were done in both the severely affected urban area of leaving them far from reaching natural herd immunity
Geneva, Switzerland, and the whole of Spain, capturing in the population.9
both strongly and less affected provinces. Both studies Such seroprevalence studies provide information
recruited randomly selected participants but excluded only about previous exposure, rather than immunity,
institutionalised populations (ie, permanent residents as no neutralising antibodies are measured. Since
of institutions such as prisons or care homes, as well as no correlate of protection for SARS-CoV-2 has
hospitalised residents), which is a clear limitation. They been formally defined, we do not know what titre
relied on IgG as a marker for previous exposure, which of neutralising antibodies would protect recovered
was detected by two assays for confirmation of positive patients from secondary infection or if non-neutralising
results. antibodies could also contribute to protection. By
The Spanish study,6 which included more than analogy to common-cold coronaviruses, immunity
60 000 participants, showed a nationwide seropreva after SARS-CoV-2 infection is thought to be incomplete
lence of 5·0% (95% CI 4·7–5·4; specificity–sensitivity and temporary, lasting only several months to a few
years.10,11 A subset of asymptomatic SARS-CoV-2 cases Geneva Centre for Emerging Viral Diseases, Geneva University Hospitals, Geneva,
Switzerland (IE); and Centre for Vaccinology, Department of Pathology and
shows a lower antibody response and titres that wane Immunology, University of Geneva, Geneva, Switzerland (BM)
quickly.12 It is unknown whether these patients are 1 Vetter P, Eckerle I, Kaiser L. Covid-19: a puzzle with many missing pieces.
protected by other immune functions, such as cellular BMJ 2020; 368: m627.
2 Wu Z, McGoogan JM. Characteristics of and important lessons from the
immunity. In summary, such individuals would not be coronavirus disease 2019 (COVID-19) outbreak in China: summary of a
detected by serological assays but might confound the report of 72314 cases from the Chinese Center for Disease Control and
Prevention. JAMA 2020; published online Feb 24. https://doi.org/10.1001/
true exposure rate. jama.2020.2648.
3 Meyer B, Torriani G, Yerly S, et al. Validation of a commercially available
In light of these findings, any proposed approach to SARS-CoV-2 serological immunoassay. Clin Microbiol Infect 2020; published
achieve herd immunity through natural infection is online June 27. https://doi.org/10.1...cmi.2020.06.024.
4 Xu X, Sun J, Nie S, et al. Seroprevalence of immunoglobulin M and G
not only highly unethical, but also unachievable. With antibodies against SARS-CoV-2 in China. Nat Med 2020; published online
a large majority of the population being infection June 5. https://doi.org/10.1...1591-020-0949-6.
5 Sood N, Simon P, Ebner P, et al. Seroprevalence of SARS-CoV-2-specific
naive, virus circulation can quickly return to early antibodies among adults in Los Angeles county, California, on
April 10-11, 2020. JAMA 2020; 323: 2425–27.
pandemic dimensions in a second wave once measures
6 Pollán M, Pérez-Gómez B, Pastor-Barriuso R, et al. Prevalence of SARS-CoV-2
are lifted. In addition, the geographical variability in Spain (ENE-COVID): a nationwide, population-based seroepidemiological
study. Lancet 2020; published online July 6. https://doi.org/10.1016/
and the dynamic of weekly increasing seroprevalence S0140-6736(20)31483-5.
rates during the early phase of the pandemic 7 Stringhini S, Wisniak A, Piumatti G, et al. Seroprevalence of
anti-SARS-CoV-2 IgG antibodies in Geneva, Switzerland (SEROCoV-POP):
highlight that these studies are only snapshots in a population-based study. Lancet 2020; published online June 11.
time and space, and reflect the circumstances of the https://doi.org/10.1...6736(20)31304-0.
8 Ng D, Goldgof G, Shy B, et al. SARS-CoV-2 seroprevalence and neutralizing
period in which they were done. As we are still in the activity in donor and patient blood from the San Francisco Bay Area.
medRxiv 2020; published online May 27. https://doi.org/10.1101/
midst of an unprecedented global health crisis, such 2020.05.19.20107482 (preprint).
seroprevalence data will continue to be necessary 9 Public Health Agency Sweden. Första resultaten från pågående
undersökning av antikroppar för covid-19-virus. May 20, 2020.
for public health authorities to estimate exposure https://www.folkhals...eter-och-press/
rates, especially in areas with little testing capacity for nyhetsarkiv/2020/maj/forsta-resultaten-fran-pagaende-undersokning-av-
antikroppar-for-covid-19-virus (accessed June 24, 2020).
acute cases. If and when a vaccine is widely available, 10 Callow KA, Parry HF, Sergeant M, Tyrrell DA. The time course of the immune
ongoing seroprevalence studies will be able to provide response to experimental coronavirus infection of man. Epidemiol Infect
1990; 105: 435–46.
information about the extent and duration of vaccine- 11 Reed SE. The behaviour of recent isolates of human respiratory coronavirus
in vitro and in volunteers: evidence of heterogeneity among 229E-related
induced herd immunity. strains. J Med Virol 1984; 13: 179–92.
We declare no competing interests. 12 Long QX, Tang XJ, Shi QL, et al. Clinical and immunological assessment of
asymptomatic SARS-CoV-2 infections. Nat Med 2020; published online
*Isabella Eckerle, Benjamin Meyer June 18. https://doi.org/10.1...1591-020-0965-6.
isabella.eckerle@hcuge.ch
Even 95% specific can cause many false positives, so maybe even Roche antibody isn't as bulletproof as initially advertised
medRxiv preprint doi: https://doi.org/10.1...5.20066407.this version posted July 7, 2020. The copyright holder for this preprint
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
It is made available under a CC-BY 4.0 International license .
Antibody testing for COVID-19:
A report from the National COVID
Scientific Advisory Panel
AUTHORSHIP: National COVID Testing Scientific Advisory Panel*
*The authors’ names, degrees and affiliations are provided at the end of manuscript.
KEYWORDS: COVID-19, SARS-CoV-2, serology, IgG, IgM, antibodies, immunoassay, ELISA,
lateral flow, exposure, epidemiology
RUNNING HEAD: Antibody testing for COVID-19
CORRESPONDING AUTHOR:
Prof Derrick Crook
Department of Microbiology, John Radcliffe Hospital, Oxford, OX3 9DU, United Kingdom
derrick.crook@ndcls.ox.ac.uk
ABSTRACT
Background: The COVID-19 pandemic caused >1 million infections during January-March
2020. There is an urgent need for reliable antibody detection approaches to support
diagnosis, vaccine development, safe release of individuals from quarantine, and population
lock-down exit strategies. We set out to evaluate the performance of ELISA and lateral flow
immunoassay (LFIA) devices.
Methods: We tested plasma for COVID (SARS-CoV-2) IgM and IgG antibodies by ELISA
and using nine different LFIA devices. We used a panel of plasma samples from individuals
who have had confirmed COVID infection based on a PCR result (n=40), and pre-pandemic
negative control samples banked in the UK prior to December-2019 (n=142).
Results: ELISA detected IgM or IgG in 34/40 individuals with a confirmed history of COVID
infection (sensitivity 85%, 95%CI 70-94%), vs. 0/50 pre-pandemic controls (specificity 100%
[95%CI 93-100%]). IgG levels were detected in 31/31 COVID-positive individuals tested ≥10
days after symptom onset (sensitivity 100%, 95%CI 89-100%). IgG titres rose during the 3
weeks post symptom onset and began to fall by 8 weeks, but remained above the detection
threshold. Point estimates for the sensitivity of LFIA devices ranged from 55-70% versus RT-
PCR and 65-85% versus ELISA, with specificity 95-100% and 93-100% respectively. Within
the limits of the study size, the performance of most LFIA devices was similar.
Conclusions: Currently available commercial LFIA devices do not perform sufficiently well
for individual patient applications. However, ELISA can be calibrated to be specific for
detecting and quantifying SARS-CoV-2 IgM and IgG and is highly sensitive for IgG from 10
days following first symptoms.