Paper and Threads

There are many types of antibody tests available, each using one of 3 different methods.  They can measure 2 different types of antibodies:  Immunoglobulin M (IgM), which usually appears first, and /or Immunoglobulin G (IgG) which usually doesn't appear until after 2 weeks.  The Infectious Disease Society of America expert panel currently recommends testing sometime between the 3rd and 4th week after symptoms develop in patients in which this information is important.  It is most helpful in symptomatic patients whose SARS-CoV-2 virus test is negative. 

But these antibody tests are not routinely recommended for an individual patient, because the presence of antibodies doesn't mean that they are immune and may give a false sense of security.  These serologic tests are most useful when screening large populations of people in order to assess the prevalence of past infections by region. Continue Reading

I live in New York City and results of 1.5 million antibody tests were recently released from the Dept of Health.  Antibody tests for Covid-19 were positive in more than 27% of NYC residents, and the numbers varied by zip codes, and boroughs.  In one zipcode more than 50% of the antibody  tests were positive, demonstrating a high incidence of Covid-19 at some time during the Spring or Summer. 

Posted by Shirley at 5:41 AM | Permalink | Comments (2)

At this time convalescent plasma is either a therapeutic "breakthrough" for Covid-19 or an unproven therapy to passively transfer antibodies from a recovered Covid-19 patient, because no randomized control trials were completed.  Thousands of patients have been given convalescent plasma and yet  Phase 3 randomized, placebo-controlled trials have not been done.  

Very specific monoclonal antibodies, which are directed against the spike protein of coronavirus, are now entering Phase 3 Clinical Trials, and hopefully these will be both effective, safe, and scientifically proven.    

Monoclonal Antibodies:

This technology was first developed in the 1970s and is now being used to create many types of therapy, including cancer "drugs".  In the classic method, cells from previously infected patients are fused with a antibody producing cells that are grown in cell cultures.  These cells become a protein factory which manufacture just one potent neutralizing antibody against the virus. They can then be infused into patients.

Several monoclonal antibody phase 3 trials were just started and everyone is hoping that these highly specific antibodies against SARS-CoV-2 will be able to prevent infection after a close contact.  Continue Reading: 

One of the monoclonal antibodies is from Lilly-NIAID (NIH) and contains one antibody to the spike protein that was made from blood of an early Covid-19 patient. They started enrolling patients on Aug 2nd and they plan to enroll 2400 subjects.  Subjects must be at high risk of infection either residing at, or working in a skilled nursing home or an assisted living facility. This is a randomized controlled study with half the patients receiving placebo.  It is also double blind meaning neither the patient, nor staff know what was administered.  Subjects will be followed up for 24 weeks.

The second monoclonal antibody, developed by Regeneron, is actually a "cocktail" of two antibodies which are directed against different places on the virus spike protein.  It too was manufactured from a recently infected Covid-19 patient. They plan to enroll 2000 asymptomatic adult patients who were exposed to a Covid-19 patient living at the same address.  The Phase 3 trial is randomized, placebo-controlled, and blinded to patient, staff, and oversight board so they won't know who received antibodies or placebo until the end of the study.  They will assess subjects for infection at 1 month and continue to follow them for 7 months for safety data.  They started enrolling patients on July 13th. 

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Some scientists and epidemiologists believe that the pandemic would be even more rapidly controlled by a simple at home antigen test that could be used like a pregnancy test.  Nasal swabs or saliva must be added to a tube containing a liquid.  A paper strip coated with the virus antibody is then dropped into the liquid/test tube, and 15 minutes later the paper strip coated with a SARS-Cov-2 antibody will tell you if the virus protein antigen is present. 

In the one video I've seen, a positive control on the strip turns pink, and the adjacent strip also turns pink if the sample reacts with the antibody - meaning the virus is present in the sample.  The sensitivity is less than the molecular test, but the test becomes positive just about the same time as the virus replicates enough to be infectious and transmissible  (read more at rapidtest.com).  That makes it a very good test for "testing, tracking, and isolating,"

       Example of positive test - paper strip in the tube.

The FDA doesn't yet have a way to evaluate these home tests - but the tests offer an easy, less expensive way to alert people who are infectious and should quarantine.  It is estimated that the paper strips could be very inexpensive ($1-2), meaning this test could be repeated every 1-2 days.   This test is a public health tool.  The current molecular Covid-19 tests are the gold standard, but are taking too long to complete, so they aren't as helpful for controlling the epidemic.

Posted by Shirley at 7:43 AM | Permalink | Comments (2)

It is hard to sort out the various tests available - but they still fall into two categories: molecular tests that amplify and then measure the virus nucleotides, and antigen tests that use a specific antibody to recognize the virus protein in the nasal sample.  Last Saturday the FDA gave Emergency Use Approval (EUA) to a Saliva Molecular Test developed by Yale and used by the NBA.  This would be lots easier, but it probably won't be widely available until they scale up production.

The Point of Care Rapid Tests (POC) are antigen tests, that must be done in Doctors Offices, Clinics, Nursing Homes, etc.  They require machines that have been developed by a company for a specific type of test, and employees must be trained to use the machines.  Antigen tests are not as sensitive as molecular tests.  They are most commonly positive when patients begin shedding virus, and turn negative within 10-14 days.  The molecular tests are positive earlier and remain positive later, even when there is dead virus in the nasopharyngeal swab sample.  Positive antigen tests should be confirmed with a molecular test if there are any questions about the diagnosis. A rapid point of care test can be done immediately, and a molecular test may take more than 4 days to a week to get a result.  The rapid tests mean that infected patients can be quarantined, their contacts traced, and isolated making it easier to control the pandemic.  Continue Reading.

Next post I will describe a rapid at "home test" that is like a pregnancy test.  But this test needs a special FDA approval and the FDA will have to give emergency use approval as a public health tool instead of a highly sensitive and reproduceable molecular diagnostic test. 

Posted by Shirley at 7:29 AM | Permalink | Comments (0)

Coronavirus testing can be done by PCR, a method to detect the genetic material of the virus, or by detecting the antigen of the virus.  The tests have different sensitivities, PCR can detect the virus when the viral load is too low to be easily passed on - or when it is detected at the end of the infection when only remnants of the virus are present.  The antigen tests are less sensitive and at the onset of the infection may be falsely negative.  But these tests can be done quickly, and in Nursing Homes, Medical Offices, and other places that have the machines and some training.

It is taking many days to get the results of the PCR test results almost everywhere, and this is unacceptable. if the tests are being done to quarantine infected people to prevent further spread, it is too late to have an impact on the infection rate.  The antigen tests are more rapid, but may need to be repeated and confirmed with a PCR test - depending on the circumstances.  Read more below.

In order to get PCR tests back faster it is possible to pool samples from different people if the virus levels in the community are low.  NYC is testing 1000s of people every day and only 1% of the tests are positive.  If samples were pooled, here from 5 people for example, and the pooled sample tested negative, time and supplies could be saved.  If the pooled sample is positive, each sample would need to be tested.  But if the pool were larger and negative, even more time and supplies would be saved. Right now in states with a high percentage of positive tests, pooling wouldn't be feasible.  But if infected patients could be identified, isolated, and their contacts tested faster, we might be able to control the pandemic better. Is there a will to do this in our country?

Could we ever have at home tests, like a pregnancy test, that cost only $1-2, and could be done each day?  They were developed, tested, and can identify patients at the time they are infective.  But it is unclear where the funding would come from to scale up these tests. We can't even get our country to wear masks to decrease the number of infections.

Next time Point of Care Antigen Tests and Rapid At Home Tests. 

Posted by Shirley at 8:34 AM | Permalink | Comments (1)