In the United States, many blood collection organizations initiated programs to test all blood donors for antibodies to SARS-CoV-2, as a measure to increase donations and to assist in the identification of potential donors of COVID-19 convalescent plasma (CCP). As a result, it was possible to investigate the characteristics of healthy blood donors who had previously been infected with SARS-CoV-2. We report the findings from all blood donations collected by the American Red Cross, representing 40% of the national blood supply covering 44 States, in order to characterize the seroepidemiology of SARS-CoV-2 infection among blood donors in the United States, prior to authorized vaccine availability. We performed an observational cohort study from June 15th to November 30th, 2020 on a population of 1.531 million blood donors tested for antibodies to the S1 spike antigen of SARS-CoV-2 by person, place, time, ABO group and dynamics of test reactivity, with additional information from a survey of a subset of those with reactive test results. The overall seroreactivity was 4.22% increasing from 1.18 to 9.67% (June 2020 – November 2020); estimated incidence was 11.6 per hundred person-years, 1.86-times higher than that based upon reported cases in the general population over the same period. In multivariable analyses, seroreactivity was highest in the Midwest (5.21%), followed by the South (4.43%), West (3.43%) and Northeast (2.90%). Seroreactivity was highest among donors aged 18-24 (Odds Ratio 3.02 [95% Confidence Interval 2.80-3.26] vs age >55), African-Americans and Hispanics (1.50 [1.24-1.80] and 2.12 [1.89-2.36], respectively, vs Caucasian). Group O frequency was 51.5% among nonreactive, but 46.1% among seroreactive donors (P< .0001). Of surveyed donors, 45% reported no COVID-19-related symptoms, but 73% among those unaware of testing. Signal levels of antibody tests were stable over 120 days or more and there was little evidence of reinfection. Evaluation of a large population of healthy, voluntary blood donors provided evidence of widespread and increasing SARS-CoV-2 seroprevalence and demonstrated that at least 45% of those previously infected were asymptomatic. Epidemiologic findings were similar to those among clinically reported cases.
Author(s): Roger Y Dodd, Bryan R Spencer, Meng Xu 1, Gregory A Foster 1, Paula Saá 1, Jaye P Brodsky 2, Susan L Stramer 3
The contribution of natural immunity should speed up the timeline for returning fully to normal. With more than 8 in 10 adults protected from either contracting or transmitting the virus, it can’t readily propagate by jumping around in the population. In public health, we call that herd immunity, defined broadly on the Johns Hopkins Covid information webpage as “when most of a population is immune.” It’s not eradication, but it’s powerful.
Without accounting for natural immunity, we are far from Anthony Fauci’s stated target of 70% to 85% of the population becoming immune through full vaccination. But the effect of natural immunity is all around us. The plummeting case numbers in late April and May weren’t the result of vaccination alone, and they came amid a loosening of both restrictions and behavior.
Researchers from the Cleveland Clinic published a study this week of 1,359 people previously infected with Covid who were unvaccinated. None of the subjects subsequently became infected, leading the researchers to conclude that “individuals who have had SARS-CoV-2 infection are unlikely to benefit from COVID-19 vaccination.”
Since mid-January, confirmed Covid-19 infections in South Africa have fallen from a record of nearly 22,000 a day to around 1,000, without a large-scale vaccination campaign or stringent lockdown. Fewer than 5% of Covid-19 tests are finding traces of the virus, a sign health agencies are missing fewer cases. The government has lifted most remaining restrictions for the country of 60 million people.
The cause of this steep decline in cases remains somewhat of a mystery. As in other countries that have at some point experienced surprising drops in Covid-19 cases — such as India, Pakistan and some parts of Brazil — epidemiologists and virologists are piecing together different explanations for why the outbreak in South Africa isn’t following patterns set elsewhere.
Those include important population groups reaching sufficient levels of immunity to slow transmission, people sticking more closely to social-distancing rules, such as wearing masks and voluntarily reducing contacts, when deaths were mounting before the decline.
A Harvard immunologist said current vaccines appear to be effective enough to end the pandemic, despite growing concerns that more infectious COVID-19 variants would severely blunt the effectiveness of the preventative treatments and set the nation back in its fight against the disease.
A leaked scientific report jointly prepared by Israel’s health ministry and Pfizer claims that the company’s covid-19 vaccine is stopping nine out of 10 infections and the country could approach herd immunity by next month.
The study, based on the health records of hundreds of thousands of Israelis, finds that the vaccine may sharply curtail transmission of the coronavirus. “High vaccine uptake can meaningfully stem the pandemic and offers hope for eventual control of the pandemic as vaccination programs ramp up across the rest of the world,” according to the authors.
The nationwide study was described by the Israeli news website Ynet on Thursday, and a copy was obtained by MIT Technology Review.
Amid the dire Covid warnings, one crucial fact has been largely ignored: Cases are down 77% over the past six weeks. If a medication slashed cases by 77%, we’d call it a miracle pill. Why is the number of cases plummeting much faster than experts predicted?
In large part because natural immunity from prior infection is far more common than can be measured by testing. Testing has been capturing only from 10% to 25% of infections, depending on when during the pandemic someone got the virus. Applying a time-weighted case capture average of 1 in 6.5 to the cumulative 28 million confirmed cases would mean about 55% of Americans have natural immunity.
Now add people getting vaccinated. As of this week, 15% of Americans have received the vaccine, and the figure is rising fast. Former Food and Drug Commissioner Scott Gottlieb estimates 250 million doses will have been delivered to some 150 million people by the end of March.
There is reason to think the country is racing toward an extremely low level of infection. As more people have been infected, most of whom have mild or no symptoms, there are fewer Americans left to be infected. At the current trajectory, I expect Covid will be mostly gone by April, allowing Americans to resume normal life.
Vaccinations, obviously, are starting to make a difference. Over 2.1 million of Illinois’ 12.7 million people have had at least their first vaccination. That’s about 17% of the state.
But something far bigger is at work: the huge number of Illinoisans who have acquired natural immunity because they were already infected, mostly without knowing it. That’s probably over 7.6 million Illinoisans – about 60% of the state.
How can that be? It’s because the actual number of infections is about 6.5 for every reported case because most cases go unreported. That’s the current number used by Marty Makary, a professor at the John Hopkins School of Medicine, who wrote in the Wall Street Journal last week. Illinois has about 1.73 million reported cases, so you just multiply that by 6.5.
The virus, in simple terms, is finding nowhere to go. Far over half of its potential victims are either naturally immune or have been vaccinated.
What will it take to finally halt the spread of the coronavirus in the U.S.? To answer that question we’ve created a simulation of a mock disease we’re calling SIMVID-19.
When you click “Run Simulation” above, you are witnessing how a disease can spread through a population and how increased levels of vaccination can stop it in its tracks.
We’re chosen to simulate a fake disease since there are too many unknowns to simulate the course of COVID-19. There are common features in how any infection spreads. When enough people are immune — through vaccination or natural immunity — a population achieves herd immunity. The disease stops spreading efficiently and starts to fade away.