In the race to develop new and better vaccines and boosters to block COVID-19, scientists are eagerly seeking laboratory tests that can measure immune responses to quickly show how well these shots are working, instead of waiting months for results of clinical trials involving tens of thousands of people.
Now, a group of top scientists, including Dr. Peter Gilbert, a biostatistician at Seattle’s Fred Hutchinson Cancer Research Center, are reporting that they have defined such measurements — or correlates of protection — for the widely used Moderna mRNA vaccine.
Correlates of protection are laboratory-derived numbers that are widely used to measure performance and update vaccines against dozens of common diseases ranging from whooping cough to influenza.
Results of their study were posted on Aug. 10 on the preprint server medRxiv, where researchers present their work without peer review, meaning it has not been subject to rigorous vetting by independent scientists prior to publication. Instead, this open science “crowd sourced” peer review can take place quickly, speeding the dissemination of important findings, while subject to public critique.
The vaccine research community has been eagerly awaiting these results since April. That is when Gilbert and his colleagues began processing immune system-response data collected from 1,391 participants in blood draws during last year’s huge, 30,000 person clinical trial for the Moderna COVID-19 vaccine.
Four tests using blood samples from trial
That trial found it 94% effective in preventing symptomatic COVID-19 disease, leading the Food and Drug Administration to issue an Emergency Use Authorization in December 2020. As of June, Moderna has shipped 217 million doses of that vaccine to the U.S. government.
Using methods developed in collaboration with Gilbert’s team, researchers at Oxford University have developed similar correlates of protection for the COVID-19 vaccine produced by AstraZeneca, which has yet to be approved in the United States. Their results, published in medRxiv in June, are being used in further studies of that vaccine.
The newly released research on the Moderna vaccine involved four different tests on samples of blood from the participants. Two of the tests measured concentrations of antibodies — tiny immune proteins induced by the vaccine — that latch onto the notorious spike proteins that dot the surface of the coronavirus. The two other tests measure the concentration of antibodies needed to block, or neutralize, the virus from infecting via its chosen target, a protein called ACE2 found on the surfaces of human cells in the lung and nose, among other locales.
Each of the four tests yielded numbers that were higher in vaccine recipients who did not experience COVID-19 than in vaccine recipients who did. Data from these tests therefore helped researchers find specific levels of antibody activity that correlated with the level of protection from disease afforded by the vaccine at set points in time after each dose.
Equipped with tools to measure whether future vaccines or boosters have raised the level of protection in the blood of volunteers, vaccine developers using these correlates might obtain early evidence on whether and how well a new formulation might work against a new COVID-19 variant.
