As battles over Covid-19 mandates roil the country, it is vital that policies be scientifically based. Well-established legal precedent gives state governments and private entities the authority to impose vaccine mandates in appropriate circumstances, but mandates must be rationally related to a legitimate health aim—protecting against the spread of an infectious disease. A recent legal battle at George Mason University, a public university in northern Virginia, illustrates what happens when they aren’t.

GMU’s reopening policy requires all students, faculty, and staff to verify their vaccination status unless they obtain a religious or medical exemption—or risk disciplinary measures including unpaid leave, loss of merit pay, and termination of employment. Todd Zywicki, a longtime professor at GMU’s Antonin Scalia Law School, objected. He had already contracted and fully recovered from Covid-19 and, as a result, acquired natural immunity, confirmed by multiple positive SARS-CoV-2 antibody tests. His physician advised him that vaccination was unnecessary.

GMU insisted. Zywicki sued, claiming that the university could not show a compelling interest that should override his autonomy and constitutional rights to refuse a vaccine made unnecessary by his naturally acquired immunity.

GMU blinked. It granted Zywicki a medical exemption allowing him to hold office hours and attend in-person events provided that he maintains six feet of distance and that he undergo free, weekly Covid tests.

The GMU policy exemplifies the type of rigid, irrational rule-making that has characterized much of the pandemic response. If an individual can demonstrate immunity via circulating antibodies after a previous Covid infection, there is no compelling reason to require him to undergo an invasive vaccination.

The CDC acknowledges that reinfection of recovered Covid-19 patients is rare. Nevertheless, it still recommends that recovered patients be vaccinated. The agency cites two reasons: first, that experts don’t know how long natural immunity protection lasts; and second, that vaccination provides a strong boost to natural immunity. The first— uncertainty about the duration of protective natural immunity—is not, by itself, a convincing reason for vaccinating previously infected individuals. The second, while true, does not provide a rationale for a vaccine mandate.

No one yet knows how long natural Covid immunity will last—but the same holds true for vaccine immunity. Indeed, the duration of follow-up of people after infection is far longer than the follow-up after vaccination; it shows that natural immunity after infection is durable and long-term, lasting at least a year. Comparison with other coronaviruses indicates that natural antibody-mediated protection in Covid-19 will likely last one to two years, and that other mechanisms of immunity (such as relying on T and B cells) persist far longer.

The recent CDC announcement recommending booster shots for vaccinated people is based on data showing waning vaccine effectiveness in halting infection over time. This may be related to the gradual decline in circulating antibodies over seven months. The increasing prevalence of the Delta variant has also clearly played a role. Vaccines are moderately less effective against the transmission of Delta. The good news, though, is that the vaccines show sustained, strong effectiveness against severe Covid disease, hospitalization, and death for all variants, including Delta.

Booster shots appear to lift antibody levels and should enhance protection against infection for fully vaccinated people. The same antibody increase appears to occur following vaccination of previously infected persons. But it is unclear when or whether such a boost is needed to protect previously infected people who have a demonstrated antibody response. Nor is it known exactly what the impact of the Delta variant will be on natural immunity.

A Kentucky study of previously infected people, some of whom were subsequently vaccinated and some of whom were not, compared 246 people who were re-infected with matched controls who were not re-infected. It found that vaccination significantly reduced the risk of re-infection. But the study relied on voluntary testing to assess re-infection. If vaccinated people were less likely to be tested, either because they believed they couldn’t be re-infected or because the vaccination made the re-infection less severe than in unvaccinated subjects, then the association between reinfection and lack of vaccination would be overestimated.

In contrast, a study of over 52,000 Cleveland Clinic employees found the incidence of infection was the same among previously infected unvaccinated employees and vaccinated employees, including those who had and had not been previously infected. None of the 1,359 previously infected subjects who remained unvaccinated was re-infected. The authors concluded that individuals with previous Covid-19 infections are “unlikely to benefit” from vaccination.

While the CDC is recommending booster shots, no one has yet suggested mandating boosters for fully vaccinated people. Even without boosters, the likelihood of vaccinated persons being infected and passing it on to others is simply too low to provide a compelling interest that should override personal autonomy.

Similarly, no institution should mandate a vaccine—in effect, a booster—for people with demonstrated natural immunity who represent a low risk of re-infection. GMU showed that it could easily accommodate professor Zywicki’s wishes. Yet, the measures the school is subjecting him to may be overkill, since he does not represent any bigger threat to his students and colleagues than those with documented vaccination. And he poses little threat to a school population that, because of the policy, is fully vaccinated.

Mandates should be imposed only when absolutely necessary and then should be applied as narrowly as possible. Institutional policies should conform with both the science and with respect for individual rights.

Photo by ROBYN BECK/AFP via Getty Images


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