Meanwhile, two conflicting studies leave question of antibody response post-Covid infection up in the air

As Covid-19 cases continue to skyrocket across the U.S., a trial of Eli Lilly’s antibody cocktail in patients hospitalized with severe SARS-CoV-2 infection has fallen flat; meanwhile, the question of how long Covid-19 antibodies stick around in patients who previously contracted the disease — and what those antibodies mean for immunity — is still up in the air.

LY-CoV555 a No-Go for Severe Covid-19

The National Institute of Allergy and Infectious Diseases (NIAID)-sponsored ACTIVE-3 trial testing Eli Lilly’s antibody drug in hospitalized Covid-19 patients is shutting down due to a lack of efficacy.

Enrollment in this trial of Eli Lilly’s antibody cocktail, LY-CoV555, was paused earlier this month due to a potential safety issue; however, NIAID clarified that this early end to the study has nothing to do with the drug’s safety and everything to do with its seeming inability to help patients hospitalized with severe coronavirus infection, Associated Press reported.

While trials for the drug are being halted in this particular population, the manufacturer noted that other studies of LY-CoV555 are moving ahead, including a National Institutes of Health (NIH)-sponsored study of the drug in patients recently diagnosed with mild-to-moderate Covid-19 — and Eli Lilly Chairman and CEO Dave Ricks holds out hope that the drug will still be beneficial for other populations with Covid-19, according to reporting from CNBC.

“It’s disappointing, of course,” Ricks told CNBC when asked about the failed trial. “We would have liked to have shown a benefit in the hospital. It doesn’t appear that that benefit is there, so this chapter of that study will close.”

Eli Lilly submitted a request for an emergency use authorization (EUA) for the drug earlier this month based on interim data displaying efficacy in recently diagnosed Covid patients with mild to moderate disease. Regeneron, which has been developing a similar antibody treatment for Covid-19, filed for an EUA of it’s own earlier this month, on the same day that President Donald Trump credited the antibody cocktail with curing his own bout with Covid-19, which landed him in Walter Reed Hospital at the start of October.

How Long Do Covid Antibodies Remain?

As pharmaceutical companies scramble to find effective therapies for Covid-19 and the race for a viable vaccine candidate continues, the question of whether Covid-19 herd immunity is even on the table continues to divide experts. For example, a recently published study from Science Immunology found that serum and saliva IgG antibodies to SARS-CoV-2 were still present in the majority of Covid-19 patients for at least 3 months prior to symptom onset; meanwhile, preliminary findings from a study of more than 350,000 people by Imperial College London — which has yet to be peer reviewed — found that the number of patients with Covid-19 antibodies declined by more than 26% over a period of three months.

In the study from Science Immunology, Jennifer L. Gommerman, PhD, of the Department of Immunology at the University of Toronto, and colleagues “profiled by enzyme-linked immunosorbent assays (ELISAs) IgG, IgA and IgM responses to the SARS-CoV-2 spike protein (full length trimer) and its receptor-binding domain (RBD) in serum and saliva of acute and convalescent patients with laboratory-diagnosed Covid-19 ranging from 3–115 days post-symptom onset (PSO), compared to negative controls,” they explained.

“We observed no drastic decline in levels of anti-spike, anti-RBD or anti-NP IgG levels over a 3-month period,” the study authors wrote. “The same was true for the antigen-specific measurements in saliva (anti-spike and anti-RBD IgG). On the other hand, similar to other findings (28, 29), IgA and IgM responses to SARS-CoV-2 antigens were found to decline in both serum and saliva. In summary, our data show that a durable IgG response against SARS-CoV-2 antigens is generated in both the saliva and serum in most patients with Covid-19.”

“This study suggests that if a vaccine is properly designed, it has the potential to induce a durable antibody response that can help protect the vaccinated person against the virus that causes Covid-19,” Gommerman said in a statement to SciTechDaily.

Meanwhile, Helen Ward, FRCP, FFPH, and colleagues from Imperial College London conducted the REACT-2 study in England, U.K., in which 365,104 adult patients self-administered three rounds of lateral flow immunoassays (LFIA) to test for IgG.

“There were 17,576 positive tests over the three rounds,” Ward and colleagues found. “Antibody prevalence, adjusted for test characteristics and weighted to the adult population of England, declined from 6.0% [5.8, 6.1], to 4.8% [4.7, 5.0] and 4.4% [4.3, 4.5], a fall of 26.5% [−29.0, −23.8] over the three months of the study. There was a decline between rounds 1 and 3 in all age groups, with the highest prevalence of a positive result and smallest overall decline in positivity in the youngest age group (18-24 years: −14.9% [−21.6, −8.1]), and lowest prevalence and largest decline in the oldest group (75+ years: −39.0% [−50.8, −27.2]); there was no change in antibody positivity between rounds 1 and 3 in healthcare workers (+3.45% [−5.7, +12.7]).”

These findings suggest the possibility that population immunity decreases over time, leading to a potential for increased risk of reinfection, the study authors argued.

“This very large study has shown that the proportion of people with detectable antibodies is falling over time,” Ward said in a statement to CNBC. “We don’t yet know whether this will leave these people at risk of reinfection with the virus that causes Covid-19, but it is essential that everyone continues to follow guidance to reduce the risk to themselves and others.”

And the question remains as to whether Covid-19 antibodies actually translate to immunity from the virus, noted Paul Elliott, FFPH, FRCP, FMedSci, coauthor of the study.

“Testing positive for antibodies does not mean you are immune to Covid-19,” he told CNBC. “It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts… If someone tests positive for antibodies, they still need to follow national guidelines including social distancing measures, getting a swab test if they have symptoms and wearing face coverings where required.”

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