The degree to which an immune response to the virus indicates a protective immunity to subsequent infection is not yet understood.
By MAAYAN JAFFE-HOFFMANInjecting syringe for vaccination (illustrative)(photo credit: INGIMAGE)
A report about someone who could be the first Israeli to die after catching COVID-19 a second time has raised questions about the degree of protective immunity conferred by infection and its implication for vaccinations.Late Wednesday, a 74-year-old man who had been admitted to Rabin Medical Center in August with coronavirus died at Sheba Medical Center in Tel Hashomer. He had tested positive for coronavirus three weeks before.According to Sheba, Prof. Galia Rahav, head of the hospital’s infectious disease laboratory, is awaiting a thorough analysis of the patient’s blood samples to determine whether the original virus was hiding in the bloodstream and reappeared, or whether this was a case of second exposure.Whatever the outcome of this particular case, it brings to the forefront that the degree to which an immune response to the virus indicates a protective immunity against subsequent infection is not yet understood.The answer could have implications for the role of vaccination in response to COVID-19. If initial exposure to the virus does not result in 100% immunity or gives only short-term immunity, effective vaccination could pose a challenge.“The assumption is that the antibodies [developed against COVID-19] stay for a longer period of time,” Eytan Ben-Ami, a senior physician at Sheba, told The Jerusalem Post. “Otherwise, there would not be vaccines being developed all over the world.”However, time could prove otherwise, said Prof. Tal Brosh, head of infectious disease at Samson Assuta Ashdod Hospital. It could be that immunity fades in a shorter time, he said.“The first people to ever get vaccinated [were inoculated] in April or May, so we only have about six months or a little more of follow-up on these people,” Brosh said. “We don’t know what will happen in a year or two years after these vaccinations.”From his perspective, there are three possible scenarios. The first is the most optimistic one: The vaccine will be effective and last an exceedingly long time without ever needing to be reactivated.In a second scenario, the vaccine will provide protection but wane over time as antibody levels decline. This would be similar to the smallpox vaccine, which proved initially effective but required that people be re-dosed after three to 10 years as protection dropped.
A final scenario would be that the vaccine loses effectiveness within as little as a year. This would be more like the flu, where the virus mutates, rendering the vaccine from the previous season ineffective against it. When the virus changes its antigens, scientists have to change the vaccine to attack the new strain.“It would mean we have to re-dose people every year,” Brosh said. “It’s bad, but it is not so bad. We can deal with revaccination.”The current vaccine candidates developed by Pfizer and Moderna offer excellent, better-than-expected 95% protection in the time frame of three to six months, during which people who were vaccinated have been monitored, he said. They also are built around modern vaccinal technology that makes it simple to change the vaccine every year.“You really don’t need to try to start from the beginning, because if the virus mutates, that means the RNA code becomes a little different,” Brosh said. “The factory can easily just change the composition of the RNA in the vaccine. It is a strength of the RNA vaccine that did not exist in all old vaccines.”If SARS-CoV-2, the scientific name for the novel coronavirus, acts anything like the 2002 SARS coronavirus, immunity is likely not so short-lived. In the 2002 SARS outbreak, those who came down with the virus were naturally immune for more than a year. Immunity started to wane between one and three years after contracting the virus.However, this 74-year-old Israeli patient is not the first person to be reinfected, hence the questions.In October, the peer-reviewed medical journal The Lancet published an article about a 25-year-old male patient from Nevada who tested positive for coronavirus on April 18, 2020, and again 48 days later on June 5. His positive tests were separated by two negative tests done during follow-up visits in May.According to The Lancet, genomic analysis of the virus showed genetically significant differences between each variant associated with each instance of infection. The 25-year-old American’s second infection, like that of the 74-year-old Israeli’s, was symptomatically more severe than the first, though he did not die.The Lancet offered several hypotheses for why the disease might have been more severe, including the possibility that “a very high dose of virus might have led to the second instance of infection and induced more severe disease”; the infection was caused by a more virulent version of the virus; or it was the result of an antibody-dependent enhancement, whereby the virus’s protective antibodies ultimately amplified the infection.Other repeat coronavirus cases have been reported from Belgium, the Netherlands, Ecuador and Hong Kong. But in most of those instances, there was no increase in the severity of symptoms.“Right now, reinfection seems like a very rare event,” Brosh told the Post. “We have more than 60 million cases of COVID around the globe and only a few dozen cases of reinfection. It is interesting and exotic, but likely has no bearing on real epidemiology.”However, since people who are diagnosed with coronavirus are not randomly rescreened for the virus after their recovery, if they were reinfected and asymptomatic, it is likely that no one would know, he said.
