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By Select Laboratory Partners
ANTIBODIES AND VACCINES
Infection with SARS-CoV-2 causes the body to produce two different kinds of antibodies: binding antibodies and neutralizing antibodies. The most commonly measured binding antibodies are IgM and IgG.
Neutralizing antibodies have been shown to prevent the coronavirus from infecting our cells. COVID-19 vaccines, such as mRNA-1273 by Moderna, NVX-CoV2373 by Novavax, and BNT162b1/2 by Pfizer, have been shown to increase the neutralizing antibody level in patients treated with the vaccine, and the levels of neutralizing antibodies in the vaccine trials generally reached or exceeded the levels obtained in patients recovering from COVID-19.1-5 Therefore, high levels of neutralizing antibodies appear to be important in our body’s ability to fight off coronavirus infection.
ANTIBODY TESTING
Currently, there is only one neutralizing antibody test approved by FDA EUA6 and the clinical application is limited by its technical challenges and costs.
Alternatively, IgG antibody testing has been proposed as a reliable, cost-effective solution to estimate the levels of neutralizing antibodies. Multiple clinical studies have shown that IgG antibody levels essentially mirror the neutralizing antibody level. In fact, the CDC has recommended using IgG antibody testing as a way
to estimate neutralizing antibody levels in a recent statement – “…because direct assessment of neutralizing antibody activity requires specialized laboratories, SARS-CoV-2 IgG titers from relatively easy-to-perform commercial assays may serve as a surrogate for assessment of neutralizing activity”.7
CLINICAL STUDIES
Studies have shown that IgG and neutralizing antibody levels are generally sustained for at least 3 months in a
study of 65 COVID-19 infected patients.8 The same studies also showed that peak levels of neutralization antibodies were achieved between 20-25 days after the onset of symptoms.8 However, the percentage of patients with high levels of neutralizing antibodies dropped from 60% to only ~17% after 65 days.8 According to the CDC, “decreasing neutralizing antibody levels over time raise concern for re-infection and could impact the implementation of immunization programs and monitoring for herd immunity”.9
Based on the clinical studies and the limited amount of clinical testing data available for the upcoming COVID-19 vaccines, it is unclear how long the vaccines will provide us with sustained, high levels of neutralizing antibodies to fight off infection. As more studies are performed and the vaccine is introduced into the general population the answer to this question will become clearer, but it is difficult to provide a definitive answer to the question with the data currently available.
Ultimately, what the clinical studies suggest is that we are unsure of how long people who receive the vaccine will remain immune to the coronavirus without additional vaccine treatment.
POST VACCINE STRATEGY
Until more clinical data is obtained from vaccine studies and a more cost-effective neutralizing antibody test becomes available, a reasonable strategy to monitor resiliency to the coronavirus in people who receive the vaccine is to follow the CDC suggestion of using the relatively easy-to-perform IgG antibody testing as means to estimate the level of neutralizing antibodies. This strategy would appear to be even more critical for at risk populations such as the elderly or people with known underlying comorbidities (e.g. hypertension, diabetes, cardiovascular disease, metabolic syndrome, obesity, etc.) who are at dramatically increased risk after contracting COVID-19.
Ultimately, frequent monitoring of how long vaccinated individuals will remain protected against the disease is extremely critical in the implementation and sustainment of COVID-19 surveillance plans and mitigation strategies.
SLP OFFERS IgG ANTIBODY TESTING BY CHEMILUMINESCENCE
. Antibody levels indicate an immune response.
. Specimen tested is serum collected in a centrifuged serum separator tube (SST).
. Serum lgG testing is a monitoring tool post-vaccine to ensure protection against COVID-19.
. FDA EUA-approved automated chemiluminescence antibody testing is one of the most sensitive at detecting low levels of antibodies in serum.
. Testing is performed in a highly complex, CLIA laboratory by qualified and highly trained laboratory technicians, eliminating the uncertainty of results identified in finger-stick, cartridge testing.
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REFERENCES:
1. Corbett, K. S., et al. Evaluation of the mRNA-1273 vaccine against SARS-CoV-2 in nonhuman primates. N Engl J Med. 2020 Oct 15;
383(16):1544-1555.
2. Jackson, L. A. et al. An mRNA vaccine against SARS-CoV-2—preliminary report. N Engl J Med. 2020; 383(20):1920-1931.
3. Keech, C., et al. Phase 1–2 trial of a SARS-CoV-2 recombinant spike protein nanoparticle vaccine. N. Engl. J. Med. 2020;
383(24):2320-2332.
4. Widge AT., et al. Durability of Responses after SARS-CoV-2 mRNA-1273 Vaccination. N Engl J Med. 2020 doi:
10.1056/NEJMc2032195.
5. Sahin U, et al. COVID-19 vaccine BNT162b1 elicits human antibody and TH1 T cell responses. Nature. 2020; 586(7830):594-599.
6. https://www.fda.gov/media/143583/download
7. https://www.cdc.gov/library/covid19/pdf/2020_10_20_Science-Update_Final-Public.pdf
8. Seow J., et al. Longitudinal observation and decline of neutralizing antibody responses in the three months following SARS-CoV-2
infection in humans. Nat Microbiol. 2020(12):1598-1607.
