Coronavirus deaths can be reduced by making recovered patients work on frontline in high-risk settings: Study
'Shield immunity' strategy may help reduce deaths from 71,000 to 58,000 while an enhanced plan can cuts deaths to 20,000, say experts
Patients who have recovered from Covid-19 could be key to minimize the pandemic’s infection rate as stay-at-home orders are lifted, according to researchers. The experts say that recovered people could replace vulnerable individuals by working at the frontline in hospitals, nursing homes, pharmacies, grocery stores and other critical institutions in which the infection spreads easily, to lower the number of interactions between susceptible people and infected people.
This strategy, which is being referred to as “Shield Immunity,” could help reduce deaths in high-transmission settings from 71,000 to 58,000 and to 20,000 under intermediate and advanced shielding plans, respectively, says the analysis published in Nature Medicine.
The objective of a shield immunity strategy is to help sustain the interactions necessary for the functioning of essential goods and services while reducing the probability of transmission.
“The core idea is to leverage a mechanism of ‘interaction substitution’ by identifying recovered individuals who have protective antibodies to SARS-CoV-2 (the virus that causes Covid-19) and deploying them back into the community. The presumed immunity of those who have recovered from the infection could allow them to safely substitute for susceptible people in certain high-contact occupations such as healthcare,” say researchers in their findings.
“Dubbed “shield immunity,” the anticipated protection against short-term reinfection could allow recovered patients to expand their interactions with infected and susceptible people, potentially reducing overall transmission rates when interactions are permitted to expand. The number of Americans infected by the novel coronavirus is likely much higher than what has been officially reported, and that could be good news for efforts to utilize their presumed immunity to protect the larger community,” says the team. It includes experts from Georgia Institute of Technology, Atlanta, US; McMaster University, Hamilton, Canada; and Princeton University, NJ, US.
Study author Dr Joshua Weitz, a professor in the School of Biological Sciences and founding director of the interdisciplinary PhD in quantitative biosciences at the Georgia Institute of Technology, explains on Twitter that “unlike herd immunity (which would lead to disastrous consequences given the severity of Covid-19), the intent of shield immunity is to dilute transmissible interactions intentionally through elevating interactions with recovered, rather than depletion of susceptibles.”
There are, however, two important caveats to the strategy. The first is that the duration of immunity to reinfection by SARS-CoV-2 remains unknown. The researchers say the individuals who survived infections by related viral infections, like SARS, had persistent antibodies for approximately two years – and those who survived infection to MERS had evidence of immunity for approximately three years. The second issue is that determining on a broad scale who has antibodies that may protect them from the coronavirus will require a level of reliable serological testing not yet available in the US, say experts.
Serological tests measure the amount of antibodies or proteins present in the blood when the body is responding to a specific infection, such as Covid-19. In other words, the test detects the body’s immune response to the infection caused by the virus rather than detecting the virus itself. However, having antibodies is not the same as having immunity to the virus. The World Health Organization (WHO) has also warned that there is currently “no evidence” that people who have recovered from Covid-19 and have antibodies are protected from a second coronavirus infection.
In the current analysis, the researchers studied the potential impacts of presumed immunity among recovered persons using a computational model of Covid-19 epidemiological dynamics. The model outlined in the study describes ways in which serological tests used to identify individuals who have been infected by and recovered from Covid-19 could help both reduce future transmission and foster increased economic engagement, says the team. The idea is to think in advance about how identifying recovered individuals could help serve the collective good, using information collected on neutralizing antibodies in new ways.
The proposed model shows that shield immunity can potentially reduce fatalities and hospitalization burden, and can be used synergistically with social distancing. In a high-transmission scenario, the analysis predicts 71,000 deaths if disease spread is not checked. However, this drops under intermediate and advanced shielding. “In a population of 10 million citizens, for example, the model predicts that in a worst-case transmission scenario, implementation of an intermediate shielding strategy could help reduce deaths from 71,000 to 58,000, while an enhanced shielding plan could cut deaths from 71,000 to 20,000. The model also suggests that shielding could enhance the effects of social distancing strategies that may remain in place once higher levels of economic activity resume,” the findings state.
In a low-transmission scenario (and population of size 10,000,000), the predicted death toll is 50,000, and this reduces to 34,000 and 8,300 under intermediate and advanced shielding plans, respectively.
Based on their results, the experts have called for identifying and deploying recovered individuals as focal points for sustaining safer interactions to develop shield immunity at the population scale.
The identification of individuals who have protective antibodies against the novel coronavirus has begun only recently. The experts acknowledge that while antibody tests are not 100% specific, implying that tests can lead to false positives, targeted use of antibody testing in groups with elevated exposure will lead to increases in positive predictive value, even with imperfect tests. “The serological antibody test differs from widespread polymerase chain reaction (PCR) testing being done to determine whether people are actively infected with the virus,” they added.
The researchers argue that among healthcare professionals, serological testing could identify recovered individuals who might then be able to interact with patients with reduced concern for infection. Other recovered individuals could be used to help reduce transmission risk in nursing homes, the food service industry, emergency medical services, grocery stores, retailing, and other essential operations. Across society, the relatively small number of individuals with immunity could substitute for people whose immunity status is not known; reducing transmission risk both for recovered individuals and those who remain immunologically naive, says the study.
“We want to think about serology as an intervention. Finding out who is immune to the coronavirus could make a big difference in trying to reduce the risk to people who would be vulnerable by interacting with someone who could pass on the disease,” explains the team.
The researchers recommend serological testing to identify those with immunity might begin with healthcare workers, who may be more likely to have been infected by the coronavirus because of their exposure to infected persons. Because so many infections do not produce the distinctive Covid-19 symptoms, many people have likely recovered from the illness without knowing they have had it, potentially expanding the pool of recovered persons.
“What this model says is that if we could identify individuals who are immune, there is a chance that some individuals would not have to reduce their level of interaction with others because that interaction would be less risky. Rather than trying to keep reducing interactions, which is helpful for reducing transmission but bad for what it does for the economy, we might be able to maintain interactions while reducing the risk, combined with other mitigation approaches,” say researchers.
The research team says ultimately, addressing the coronavirus pandemic will require the development and mass production of a vaccine that could boost immunity levels beyond 60% in the general population. Until that is available, the team believes that countries will have to use a combination of strategies to combat Covid-19, and shield immunity could potentially become part of the approach to the challenge.
According to experts, there are also ethical issues with the shield immunity approach. Using antibody information about individuals would create potential privacy issues, and require that those individuals make informed decisions about accepting additional risks for the greater good of the community, caution experts.
“For the strategy to work, recovered antibody-positive people must be issued some sort of ‘corona certificate’ or, as some have suggested, a ‘corona passport’. This means informing others, including employers, about a person’s status as immune or not. Since there is no or little stigma attached to Covid-19 status, giving up the right to privacy, in this case, maybe a small cost relative to the substantial gains for others,” writes Ole F Norheim from the University of Bergen, Bergen, Norway, in a commentary. He was not involved in the study.
“However, if a proportion of patients suffer long-term complications as a result of Covid-19, protecting privacy against employers and insurance agencies will be much more important. Whether giving up the right to privacy in a crisis could lead to an erosion of this right to privacy for health-related data forever needs to be considered carefully. For these reasons, the ‘recovered-individuals’ strategy should not be mandatory, it should last for a short period, and there must be an opt-out mechanism in place,” says Norheim in the article published in Nature Medicine.
The expert argues that since a recovered status may provide additional benefits, such as employment, the strategy of allowing only those previously infected back into society “can create perverse incentives” such that some people might try to become infected to go back to work. “Ultimately, decision-makers must take a stand on whether to embrace the immunity strategy or not. As scientific understanding improves the safety and efficacy of this strategy, and even if there are some valid counter-arguments, I foresee wide acceptance of this strategy on ethical grounds. It will maximize lives saved at a lower cost and with burdens more fairly distributed, relative to most other alternative policies,” says Norheim.