Natural immunity from contracting coronavirus provided Israelis with longer-lasting protection against the Delta variant than two shots of the Pfizer vaccine given early this year, new Israeli research suggests.
The study by Maccabi Healthcare Service looked at individuals who had either gotten two shots of the vaccine by the end of February or tested positive for COVID-19 by that time.
It compared 46,035 Maccabi members who caught the coronavirus at some point during the pandemic and the same number of double-vaccinated people.
People who had two vaccine shots had a six-fold higher chance of getting infected with Delta than patients who hadn’t been vaccinated but previously contracted the coronavirus, according to the research.
The study, published online but not yet peer reviewed, is the largest of its kind. It doesn’t take booster shots — now widely given in Israel — into account, but given that most of the world is still giving a two-dose regimen, has international relevance.
But experts are stressing that the results shouldn’t be interpreted as discouragement from vaccinating. Immunologist Prof. Cyrille Cohen of Bar Ilan University, who was not involved in the study, told The Times of Israel: “Certain people who are not inclined to get vaccinated might be mistaken and think that this means you’d better get sick a priori and not get a vaccine. Such a thinking is medically wrong, and the results of the study do not mean that people should expose themselves on purpose and get sick.
“As with other disease, it is much safer to get the vaccine and prevent COVID-19, a disease that puts one at risk of hospitalization, death and long-running after-effects.”
In the two groups, there were 748 cases of SARS-CoV-2 breakthrough infections, 640 of which were in the vaccinated group and 108 in the previously infected group, which was relying on natural immunity alone.
The vaccine-dependent people had a seven-fold higher chance of symptomatic infection, and a 6.7-fold higher chance of being hospitalized.
In addition, a sample of 16,215 who were infected during Israel’s third wave in January-February 2021 was compared to an equal number of people vaccinated during that period. The contrast for these two groups was even starker: It showed that Delta had a 27-fold higher chance of breaking through vaccine protection from January and February and causing symptoms than breaking through natural immunity acquired in the same period and causing symptoms.
The study also found that when recovered patients boosted their natural protection with a single vaccine shot — as recommended by Israeli health officials — their protection reached new highs, and they had approximately half the infection risk of other recovered patients.
“Individuals who were previously infected with SARS-CoV-2 and given a single dose of the vaccine gained additional protection against the Delta variant,” the study suggested.
“The long-term protection provided by a third dose, recently administered in Israel, is still unknown.”
The authors, led by Dr. Sivan Gazit, deputy head of Maccabi’s research arm, noted that their study is significant for taking a wide time-frame and using a large data sample. They wrote: “Our large cohort, enabled by Israel’s rapid rollout of the mass-vaccination campaign, allowed us to investigate the risk for additional infection — either a breakthrough infection in vaccinated individuals or reinfection in previously infected ones — over a longer period than thus far described.”
Cohen said of the study: “The data presented is important and can draw a kind of immune hierarchy. From the most protected to the less, there are vaccinated convalescent, convalescent, then vaccinated and then preople who choose not to vaccinate, who are the most vulnerable.”