When the new Green Pass rules for who can enter certain venues take effect in Israel Sunday, recovered coronavirus patients will no longer be eligible for the pass unless they recovered less than six months ago or have received one dose of the vaccine.
More than 1.2 million Israelis have recovered from the virus. About 443,000 recovered more than six months ago but haven’t been vaccinated. And though there are questions about exactly how protected recovered patients are, experts agree that a single vaccine dose increases their protection level.
How protected are recovered patients?
Experts generally agree that recovery provides good protection over time, especially against severe illness. Reinfection has consistently proven rare, and a preliminary study published in America in November predicted that this immunity would last for years.
During the latest wave of the virus, however, this immunity began to crack, either because of the time that had passed since recovery or because the delta variant is more infectious. Recovered patients are still infected at much lower rates than people who received two doses of the vaccine, but the rate is rising.
Has this subject been studied in Israel?
Yes, repeatedly. One study by the Gertner Institute, whose findings were presented to the government’s expert advisory panel on the virus September 2, examined infections contracted between July 11 and August 27.
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The study found that of 96,845 people who contracted the virus during the first wave (March-April 2020) but weren’t vaccinated, only 880 got reinfected this summer and only two were seriously ill. And of 96,882 recovered patients who also got one dose of the vaccine, only 246 were reinfected while three became seriously ill.
Similarly, of the 184,969 unvaccinated people who became ill during the second wave (the alpha variant), only 796 were reinfected and nine became seriously ill. And of the 55,423 recovered patients who had also gotten one vaccine dose, only 89 were reinfected while none were seriously ill.
What did the experts say about the Green Pass?
Based on the above data, the experts concluded that unvaccinated recovered patients still enjoy high protection against serious illness and are somewhat less likely to be reinfected. Consequently, at that September 2 meeting, most of them voted against requiring recovered patients to be vaccinated in order to keep their Green Pass.
However, they agreed that recovered patients should be allowed to get one vaccine dose if they had recovered more than three months ago.
When did they change their minds, and why?
By September 14, most of the experts had changed their mind and concluded that after some period of time, recovered patients should be required to get one vaccine dose to keep their Green Pass. But they disagreed over the length of that period.
The change was because the study presented on September 2 had since been expanded and included new data. The new data showed that people who recovered and received one vaccine dose had the same protection as people who were never infected but received three vaccine doses.
Unvaccinated recovered patients were also fairly well protected for the first 10 months, though only about half as protected as people vaccinated with three doses. But after 10 months, the protection level dropped to only a quarter of the level enjoyed by people vaccinated three times. The study also found that reinfection rates were rising among younger recovered patients.
How significant are antibody levels?
Antibody levels are considered a key measure of how protected people are against the virus. Though antibodies aren’t the only factor in the body’s immune response, studies do show a correlation between low antibody levels and lower protection against the virus.
How quickly and how far do recovered patients’ antibody levels decline?
The answer isn’t clear, because it can depend on many variables, including age, preexisting conditions and length of exposure to the virus.
But some clues are provided by Magen David Adom’s blood bank, to which recovered patients have been donating for almost a year to help coronavirus patients. Around 8,000 have done so, many more than once.
“We saw that only a third of [unvaccinated] recovered patients had medium or high antibody levels,” said the blood bank’s director, Prof. Eilat Shinar. “Moreover, we see a decline in antibody levels in the same person from donation to donation, of about half a percent per day. We invite donations only until they fall to a certain antibody level below which we decided not to accept donations anymore. This phenomenon spans ethnic communities, genders and age.”
Another study, of 1,000 children hospitalized at Jerusalem’s Shaare Zedek Medical Center for various reasons, found that among children whose date of infection with the virus was known, most had no measurable antibodies after four months.
“We still have a limited understanding of everything to do with antibodies,” said Prof. Yechiel Schlesinger, the head of Shaare Zedek’s pediatric hospital. “With regard to the coronavirus, there are still many things we don’t know about the immune system. What we do know is that giving one dose of the vaccine dramatically increases the antibody level.”
Why aren’t recovered patients given blood tests before they get vaccinated?
There are several reasons. One is that it’s still not clear when antibody levels begin waning, so a person who currently has a high antibody level could see it plummet soon afterward. There are also financial and logistical arguments against it. Moreover, the vaccine is considered both safe and effective for recovered patients, so there’s no reason not to give it even if the patient’s antibody level is still high.
Why are recovered patients now being required to vaccinate after six months?
The reason for this decision isn’t clear, as the experts didn’t explain it in the minutes of the meeting at which the decision was made. What is known is that some experts thought six months was too short a time, and that recovered patients should be allowed more time before they have to get vaccinated to keep their Green Pass. After all, the Gertner Institute study found that the major drop-off in antibody levels occurred only after 10 months.
“I would have extended this to a year,” said Prof. Gili Regev-Yochay of the Gertner Institute. “Even our initial data shows that it’s closer to a year than half a year. And we know beyond doubt that they are more protected than people who were vaccinated with only two doses.”
But other experts argued that given the likely arrival of new variants, it was better not to wait too long to vaccinate recovered patients.
In the end, since the experts couldn’t agree, the decision was made by Health Ministry officials.