COVID-19 immunity lasts only six months, reinfection possible - study

Since there is no treatment or vaccine for the novel coronavirus, the only way to stop its spread is through social distancing and good hygiene.

Shoppers wear face masks and walk around a fashion shopping center in Ashdod, as restrictions over the coronavirus disease (COVID-19) ease around Israel, May 5, 2020.  (photo credit: AMIR COHEN/REUTERS)
Shoppers wear face masks and walk around a fashion shopping center in Ashdod, as restrictions over the coronavirus disease (COVID-19) ease around Israel, May 5, 2020.
(photo credit: AMIR COHEN/REUTERS)
Getting re-infected by the novel coronavirus could be possible within six months of recovery, according to a new study published by a team in Amsterdam. If that is the case, then Israel’s hope of testing 1 million Israelis for antibodies to SARS-CoV-2 partially to keep the economy open in any subsequent rounds may be shattered.
A team of 13 researchers recently uploaded a paper to Medrxiv, an internet site that distributes unpublished manuscripts about health sciences, after monitoring 10 subjects who had contracted at least one of four species of seasonal coronaviruses over a time span of 35 years (1985 to 2020).
In “Human Coronavirus Reinfection Dynamics: Lessons for SARS-CoV-2,” they claim that “an alarmingly short duration of protective immunity to coronaviruses was found... We saw frequent reinfections at 12 months post-infection and substantial reduction in antibody levels as soon as six months post-infection.”
Since there is no treatment or vaccine for the novel coronavirus, or COVID-19 – the disease to which it leads – the only way to stop its spread is through social distancing and good hygiene. As such, long-term protective immunity could impact the overall course of the pandemic, the post-pandemic period and any subsequent waves. Until now, this concept has been a key component of the Health Ministry’s second wave strategy.
The Health Ministry recently revealed that it had purchased serological tests with the aim of surveying as many as 1 million people to determine how much of the public has been infected. Since around 80% of people who get the virus show little or no symptoms, they can carry and spread it without knowing.
However, “serology-based tests that measure previous infections for SARS-CoV-2 may have limited use if that infection has occurred more than one year prior to sampling,” the Amsterdam researchers explained.
Relatedly, there has been ongoing discussion about herd immunity, the idea that when a threshold proportion of a population is immune to a certain pathogen this protects even non-immune individuals against the infection by limiting the overall spread. Such a concept has proven effective with a variety of other viruses, including hepatitis and influenza A. However, achieving herd immunity may be challenging due to rapid loss of protective immunity, if the Amsterdam study is correct.
“It was recently suggested that recovered individuals should receive a so-called ‘immunity passport,’ which would allow them to relax social distancing measures,” the authors explained. “However, as protective immunity may be lost by six months post infection, the prospect of reaching functional herd immunity by natural infection seems very unlikely.”
Moreover, if the study is correct, then a seasonal rather than one-time vaccine may be necessary to circumvent ongoing transmission.
Oren Kobiler, a senior lecturer in the Department of Microbiology and Immunology at Tel Aviv University’s School of Medicine told The Jerusalem Post that the study does not surprise him.
“We know that people can be infected with human coronaviruses time after time,” he said. “One question is whether, like with these coronaviruses, immunity to SARS-CoV-2 does not last long. But a better question is whether the immunity is sterile or non-sterile.”
Sterile immunity means that a person cannot be re-infected. Non-sterile immunity means that a person can be re-infected but that he or she will not develop a serious case of the disease.
“You don’t really need sterile immunity,” Kobiler said. “With non-sterile immunity, you could be re-infected and have two days of common cold – no severe symptoms – and that would be good enough for all of us, I think.”
He explained that the seasonal influenza vaccine has about a 50% to 70% success rate for preventing infection. However, when one looks at how many people who got the vaccinations develop severe cases, the percentage is much lower.
This suggests that people who contracted the novel coronavirus, even if they are re-infected, would likely not be in grave danger or pose the risk of overwhelming the health system.
“But we are not sure this really happens with this coronavirus,” Kobiler said, noting that it has only been around five months since the first recorded cases of SARS-CoV-2, and therefore “there is no good evidence yet.”
Since the start of the pandemic, there have been examples of reinfection but most of the time they were assumed to be tied to faulty testing. In mid-April, South Korea reported more than 100 people had been re-infected.
At that time, Prof. Ronit Sarid, an expert in virology at Bar-Ilan University, told the Post that, “We don’t know any virus that causes reinfection within a month or two after the first infection.”
Kobiler added that there is reason to believe that this coronavirus may be different from the four strands tested by the Amsterdam team, since administering plasma to patients with acute COVID-19 has been shown to improve outcomes.
Since the beginning of April, Israel has been using plasma as a “passive vaccine” to treat Israelis who are severely ill.
“When people are exposed to any disease, they develop antibodies,” Magen David Adom deputy director-general of blood services Prof. Eilat Shinar explained.
Passive immunization is when you get those preformed antibodies. An active vaccine, in contrast, is when you are injected with a dead or weakened version of a virus that tricks your immune system into thinking that you have had the disease and your immune system creates antibodies to protect you.
Kobiler said that if this is the case then serological testing could still be valuable, especially if we assume that a second wave could occur by as early as December.
“If these people have immunity even for six months, so they could not be re-infected in a second wave – but in a third or fourth,” he said.
Furthermore, Dr. Elon Ganor, a medical professional and serial entrepreneur, told the Post that the public should be cautious in taking the new study as fact, describing it as “an assumption with no absolute proof.”
He said, “This article does not give us any … proof of the length of the COVID-19 immunity and the chances for reinfection. It is highly speculative.”