The sheer number of vaccinated Israelis means some breakthrough infections were inevitable, and the unvaccinated are still far more likely to end up in the hospital or die. But Israel’s experience is forcing the booster issue on to the radar for other nations, suggesting as it does that even the best vaccinated countries will face a Delta surge.
Now, the effects of waning immunity may be beginning to show in Israelis vaccinated in early winter; a preprint published last month by physician Tal Patalon and colleagues at KSM, the research arm of MHS, found that protection from Covid-19 infection during June and July dropped in proportion to the length of time since an individual was vaccinated. People vaccinated in January had a 2.26 times greater risk for a breakthrough infection than those vaccinated in April. (Potential confounders include the fact that the very oldest Israelis, with the weakest immune systems, were vaccinated first.)
Cases in the country, which were scarcely registering at the start of summer, have been doubling every week to 10 days since then, with the Delta variant responsible for most of them. They have now soared to their highest level since mid-February, with hospitalizations and intensive care unit admissions beginning to follow. How much of the current surge is due to waning immunity versus the power of the Delta variant to spread like wildfire is uncertain.
What is clear is that “breakthrough” cases are not the rare events the term implies. As of 15 August, 514 Israelis were hospitalized with severe or critical Covid-19, a 31% increase from just 4 days earlier. Of the 514, 59% were fully vaccinated. Of the vaccinated, 87% were 60 or older. “There are so many breakthrough infections that they dominate and most of the hospitalized patients are actually vaccinated,” says Uri Shalit, a bioinformatician at the Israel Institute of Technology (Technion) who has consulted on Covid-19 for the government. “One of the big stories from Israel [is]: ‘Vaccines work, but not well enough.’”
Boosters are unlikely to tame a Delta surge on their own, says Dvir Aran, a biomedical data scientist at Technion. In Israel, the current surge is so steep that “even if you get two-thirds of those 60-plus [boosted], it’s just gonna give us another week, maybe 2 weeks until our hospitals are flooded.” He says it’s also critical to vaccinate those who still haven’t received their first or second doses, and to return to the masking and social distancing Israel thought it had left behind—but has begun to reinstate.
Aran’s message for the US and other wealthier nations considering boosters is stark: “Do not think that the boosters are the solution.”