Another group, writing in The new English medical journal earlier this month, he detailed the path of the virus in a 45-year-old man with an autoimmune disease for which he was receiving immunosuppressants. In this case, they found that there was an “accelerated” evolution of the virus in the individual, and many of the mutations occurred in the peak protein. Most immunocompromised people eliminate SARS-CoV-2 infections without further complications, they wrote, but “this case highlights the potential for persistent infection and accelerated viral evolution associated with an immunocompromised state”.
The same phenomenon has been observed in other conditions where the immune system is impaired. HIV attacks immune function, which allows it to evolve at a surprisingly high rate, making it even more difficult for the body to continue producing antibodies that bind and neutralize the virus. By the same mechanism, HIV infections allow other viruses in the individual to last and transform. The herpes simplex virus can develop unusual drug resistance in AIDS patients, for example.
Still, we need to better understand exactly which immunocompromised patients are most vulnerable to prolonged SARS-CoV-2 infection. The category of “immunocompromised” captures a wide range of different conditions and not all of them can confer the same risk of persistent Covid-19. Brian Wasik, a virologist at Cornell University, points out that the term may include people born with rare diseases that diminish their ability to fight pathogens, as well as those who are taking immunosuppressants to enable a transplant or suppress an autoimmune disease.
Evidence for the links between immunocompromised individuals and persistent SARS-CoV-2 infections and between persistent infections and viral evolution is compelling enough to be considered in discussions about vaccine priority. On Sunday, a panel from the United States Centers for Disease Control and Prevention recommended that immunocompromised people be placed in “Phase 1c” – the third wave – of vaccine launch. This means that they must receive the injections at the same time as those with cancer, coronary heart disease or obesity, among other conditions. This decision aimed to address the specific risks posed by Covid-19 for people with immune system problems, but left out the possibility that vaccinating these individuals could help prevent the development of new variants of SARS-CoV-2 that would make this pandemic even worse than it already is. For this reason, although there are only a handful of directly relevant case reports, public health officials should consult virologists about whether it would be wise to transfer immunocompromised people to the previous Phase 1b group.
At the very least, we need to better monitor possible changes in SARS-CoV-2. The US government must do more to help organize viral sequencing efforts. The CDC has a program called Spheres that tried to capture sequence data during the pandemic, but it falls short: where the UK has sequenced about 10% of its Covid-19 cases, the United States has managed just 0.3%. “It’s a little irregular,” says Adam Lauring, of the University of Michigan School of Medicine, who adds that his team has loaded about 2% of the data for sequence variants in the U.S. “There are vast areas of the country where there are no people who spend a lot of time and effort” on this task. Better monitoring of viral evolution can also help to clarify the question of where exactly – in which sick people – these changes are most likely to accumulate.
While monitoring SARS-CoV-2 mutations, we have to recognize that understanding its epidemiological and clinical significance requires more work. Meanwhile, the virus is still rampant, which offers more opportunities for mutation, even as it spreads from person to person. But long-term infections in some immunocompromised individuals and the associated potential for viral evolution should be a focus of attention.
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