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"Just 8 of the 986 individuals tested on March 26 and 27 were positive for SARS-CoV-2 antibodies. Another 23 were borderline"
Serologic antibody tests not only can confirm suspected cases after the fact, they can also reveal who was infected and didn’t know it. Up to a quarter of people with SARS-CoV-2 infection may unwittingly spread the virus because they have mild or no symptoms.
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" As infectious disease epidemiologists, we wish to state clearly that herd immunity against COVID-19 will not be achieved at a population level in 2020"
To reach herd immunity for COVID-19, likely 70% or more of the population would need to be immune. Without a vaccine, over 200 million Americans would have to get infected before we reach this threshold. Put another way, even if the current pace of the COVID-19 pandemic continues in the United States – with over 25,000 confirmed cases a day – it will be well into 2021 before we reach herd immunity. If current daily death rates continue, over half a million Americans would be dead from COVID-19 by that time.
As we discuss when and how to phase in re-opening,10 it is important to understand how vulnerable we remain. Increased testing will help us better understand the scope of infection, but it is clear this pandemic is still only beginning to unfold.
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Coronavirus antibodies dwindled to undetectable levels after just 2 or 3 months for 40% of asymptomatic people and 13% of symptomatic people.
Overall, asymptomatic people showed "a weaker immune response" in the months after they were exposed to the coronavirus.
A poor immune response in people who recover from the virus may not bode well for the development of an effective vaccine.
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5% of covid-19 infected people in Spain developed antbodies
Seroprevalence was 5·0% (95% CI 4·7–5·4) by the point-of-care test and 4·6% (4·3–5·0) by immunoassay, with a specificity–sensitivity range of 3·7% (3·3–4·0; both tests positive) to 6·2% (5·8–6·6; either test positive), with no differences by sex and lower seroprevalence in children younger than 10 years (<3·1% by the point-of-care test). There was substantial geographical variability, with higher prevalence around Madrid (>10%) and lower in coastal areas (<3%). Seroprevalence among 195 participants with positive PCR more than 14 days before the study visit ranged from 87·6% (81·1–92·1; both tests positive) to 91·8% (86·3–95·3; either test positive). In 7273 individuals with anosmia or at least three symptoms, seroprevalence ranged from 15·3% (13·8–16·8) to 19·3% (17·7–21·0). Around a third of seropositive participants were asymptomatic, ranging from 21·9% (19·1–24·9) to 35·8% (33·1–38·5). Only 19·5% (16·3–23·2) of symptomatic participants who were seropositive by both the point-of-care test and immunoassay reported a previous PCR test.
Interpretation
The majority of the Spanish population is seronegative to SARS-CoV-2 infection, even in hotspot areas. Most PCR-confirmed cases have detectable antibodies, but a substantial proportion of people with symptoms compatible with COVID-19 did not have a PCR test and at least a third of infections determined by serology were asymptomatic. These results emphasise the need for maintaining public health measures to avoid a new epidemic wave.
Funding
Spanish Ministry of Health, Institute of Health Carlos III, and Spanish National Health System.
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Early Herd Immunity against COVID-19: A Dangerous Misconception
To reach herd immunity for COVID-19, likely 70% or more of the population would need to be immune. Without a vaccine, over 200 million Americans would have to get infected before we reach this threshold. Put another way, even if the current pace of the COVID-19 pandemic continues in the United States – with over 25,000 confirmed cases a day – it will be well into 2021 before we reach herd immunity. If current daily death rates continue, over half a million Americans would be dead from COVID-19 by that time.
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Scientists at King's College London showed detectable antibodies but levels began to wane over the three months of the study.
Our immune system is the body's defence against infection and it comes in two parts.
The first is always ready to go and leaps into action as soon as any foreign invader is detected in the body. It is known as the innate immune response and includes the release of chemicals that cause inflammation and white blood cells that can destroy infected cells.
But this system is not specific to coronavirus. It will not learn and it will not give you immunity to the coronavirus.
Instead you need the adaptive immune response. This includes cells that produce targeted antibodies that can stick to the virus in order to stop it and T cells that can attack just the cells infected with the virus, called the cellular response.
It is not known if people who have only mild symptoms, or none at all, will develop a sufficient adaptive immune response.
Understanding of the role of T-cells is still developing.
But a recent study found people testing negative for coronavirus antibodies may still have some immunity.
For every person testing positive for antibodies, it was found two had specific T-cells which identify and destroy infected cells.
The new coronavirus, Sars-CoV-2, has not been around long enough to know how long immunity lasts, but there are six other human coronaviruses that can give a clue.
Four produce the symptoms of the common cold and immunity is short-lived. Studies showed some patients could be re-infected within a year.
But the common cold is generally mild. There are two more troublesome coronaviruses - the ones that cause Severe Acute Respiratory Syndrome (Sars) and Middle East Respiratory Syndrome (Mers) - in which antibodies have been detected a few years later.
"The question is not whether you become immune, it's how long for," said Paul Hunter, a professor in medicine at the University of East Anglia.
He added: "It almost certainly will not last for life.
"Based on antibody studies in Sars it is possible that immunity will only last about one to two years, though this is not yet known for certain."
Another issue is that just because you might be protected by your antibodies, it doesn't mean you cannot still harbour the virus and pass it onto others.
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Coronavirus Antibodies May Not Make You Immune, WHO Warns
What serological tests, also known as antibody tests, do show, according to WHO experts, is whether a person has contracted the virus in the past, but the level of antibodies alone does not necessarily indicate future immunity.
“Nobody is sure,” executive director of emergencies programs Dr. Michael J. Ryan said of the likelihood that someone with antibodies could be reinfected.
Ryan added that some tests give false negative results.
While someone who “generates a full-blown immune response” detectable by serological tests could likely expect immunity for some time, “we just don’t know what that period of time is,” Ryan said.
He also emphasized that, at present, it is likely “quite a low proportion of people” have these antibodies, suggesting that widespread immunity is still a distant goal.
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German research suggests infection offers little immunity to coronavirus
A research projected completed in the German state of Bavaria found that people infected with coronavirus lose their antibodies to the virus just months after beating the disease, giving rise to concerns about the effectiveness of vaccinations and herd immunity.
The research project, completed by the Munich Clinic Schwabing, found that the concentration of antibodies in the blood decreases rapidly in the months following an infection.
The findings dampen hope of long-lasting immunity for those who have beaten the virus.
The findings give credence to reports out of South Korea and China that some people had been infected with the virus despite having previously recovered from it.
The project looked at patients who had recovered from the virus from January onwards.
It found that while neutralising antibodies were formed in the blood during the time in which the person was infected, these declined in the following months.
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Adverse Effects of Immunoglobulin Therapy
The majority of these events, such as flushing, headache, malaise, fever, chills, fatigue and lethargy, are transient and mild. However, some rare side effects, including renal impairment, thrombosis, arrhythmia, aseptic meningitis, hemolytic anemia, and transfusion-related acute lung injury (TRALI), are serious. These adverse effects are associated with specific immunoglobulin preparations and individual differences. Performing an early assessment of risk factors, infusing at a slow rate, premedicating, and switching from intravenous immunoglobulin (IVIG) to subcutaneous immunoglobulin (SCIG) can minimize these adverse effects. Adverse effects are rarely disabling or fatal, treatment mainly involves supportive measures, and the majority of affected patients have a good prognosis.
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