A covid-19 vaccine dose is placed on a table at Hillel Yoffe Medical Center, in a photo taken December 20, 2019, in Hadera (Israel Photo: Amir Levy ( Getty Images)
Officials in Israel said Monday that the Delta strain of the coronavirus is more effective than previous strains in infecting fully vaccinated individuals. Outside scientists have not yet confirmed their findings, but vaccinated individuals are still protected from more severe illness and death due to the variant.
The Israel Ministry of Health claims that the Pfizer/BioNTech vaccine only 64% effective in preventing infection from Delta. This is a stark contrast to the 94% effectiveness of earlier versions of this virus. The health ministry said that the vaccine's effectiveness against serious illness or hospitalization had declined slightly. The Pfizer vaccine prevented serious illness from Delta at 94%, as compared to 98% in the past.
Delta is more transmissible that previous strains of coronaviruses, even earlier variants that were more transmissible that the ones that triggered the pandemic in the first half of last year. These aren't the first findings to show that Delta poses a greater challenge to an immune system that is trained to recognize wild-type strains. According to lab data, the immune systems of people who have been vaccinated produce less antibodies than those that are capable of neutralizing Delta. These antibodies play an important role in keeping infection from happening.
The public has not been provided with the data or the analysis that was used to arrive at these estimates from Israel. According to Haaretz, some Israeli experts have raised concerns that the Ministry of Health's model might be misleading about the Pfizer vaccines resilience in the face of Delta.
Public Health England has released case data from the UK that shows that two doses of either the Pfizer/BioNTech vaccines or the Oxford/AstraZeneca vaccinations provide the same protection against symptoms of Delta as the past strains (88% for Pfizer). Israel's data reflect both symptomatic as well as asymptomatic disease, so these numbers may not be in conflict. Delta may infect more people who have been fully vaccinated but is less likely to make them sick.
It is important to remember that these vaccines were initially tested for their ability to prevent infection from the coronavirus. Data began to emerge shortly after the vaccines were released to the public that showed the Moderna and Pfizer mRNA vaccines were highly effective in preventing infection. This reduced the risk of transmitting the disease. Although it is possible that silent infections are more common in Delta, it would not make the vaccines a failure. The overall data shows that the vaccines, including Johnson & Johnson's one-shot version, are about as effective in preventing the worst effects of Delta than they were against other strains.
Experts remain concerned that the emergence and spread of Delta could cause new outbreaks of illness and even death in highly vaccinated nations like the U.S., UK and Israel. Although most of the harm will be to those not vaccinated against the coronavirus have yet to be exposed, it is important to know the risks that covid-19 may pose to anyone who has been infected. There is always the chance that the virus could mutate sufficiently to escape our immunity if the pandemic is not controlled.