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Following infection with the SARS-CoV-2 infection, the adaptive immune system produces neutralizing antibodies that attack the virus and prevent further illness in those who recover. Vaccination provides another means of developing long-lasting immunity. However, neutralizing antibody concentrations decline with time following vaccination or previous infection. Authors of a recent report created a model for predicting the decline of neutralizing antibody concentrations over time and what is needed to maintain long-term immunity.

Those who recover from SARS-CoV-2 infection have an estimated 89 percent protection from reinfection, while vaccine protection estimates range from 50 percent to 95 percent. There is concern that new variants may bypass immune protection in vaccinated and previously infected people. Predictive models of immunity may guide the distribution of vaccines and vaccine boosters as the pandemic progresses.

The researchers combined and standardized data from trials studying the neutralizing antibody response to seven different vaccines and data from a group of recovered participants. They created a model based on previous research of the influenza virus to estimate the concentration of antibodies needed to provide 50 percent protection against SARS-CoV-2 infection. Lastly, they used their model to predict the efficacy of a new vaccine released in March 2021.

The authors reported that the antibody concentration needed to provide 50 percent protection is just 20 percent of the average concentration in recovered people three to four months following infection. The concentration needed to prevent severe COVID-19 disease is only 3 percent of convalescent levels. Using their model, the investigators predicted a significant decline in antibody concentration over 250 days following vaccination; however, the predicted concentration is still high enough to prevent severe disease. The model was also highly effective in predicting the efficacy of a new vaccine (79 percent estimated efficacy, 81 percent reported efficacy).

The authors noted that methods for measuring neutralizing antibody activity and recovery status varied widely among the studies they used to create the model, which may decrease its efficacy; however, early use of the model provided accurate results.

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