How long do antibodies last? Which patients get hit the hardest? How does the vaccine handle the Delta variant? The latest scientific findings from Israel.

Israel has led the world in getting its citizens vaccinated, so it’s no surprise that it has also become a center for groundbreaking research into the effects and effectiveness of the Pfizer-BioNTech vaccine against the novel SARS-CoV-2 coronavirus.

How did the vaccine stand up to the original Wuhan variant, then the British and South African variants, and now the Indian (Delta) variant of the virus? How long do antibodies last? In which patient populations are infections worst and vaccinations least effective?

All these questions, and more, are being investigated in Israeli labs.

Here’s a synopsis of research published between January and July:

• COVID-19 antibody levels vary according to age and gender, reported Tel Aviv University computational genomic researcher Noam Shomron and Shamir Medical Center’s Dr. Adina Bar Chaim. Analyzing more than 26,000 blood samples revealed that infected females with symptoms have the strongest immune reaction after age 50. Symptomatic infected males have the strongest immune reaction around age 35. The scientists believe hormones account for these differences. They also noted that the immune response was four times stronger in vaccinated people than in recovered COVID-19 patients.
• Older individuals with many underlying medical conditions and immunosuppression are more prone to coronavirus infection and a severe case of COVID-19, even after being fully vaccinated, according to a 17-hospital study published in July, led by Dr. Tal Brosh, head of the Infectious Disease Unit at Samson Assuta Ashdod Hospital.
• mRNA vaccines such as Pfizer’s do not negatively impact fertility, according to an observational study published in Reproductive Biology and Endocrinology, by a team led by Dr. Raoul Orvieto, director of Sheba Medical Center’s IVF Fertility Clinic. Fully vaccinated couples in the study showed no differences in sperm quality, semen volume, ovarian stimulation or proportion of high-quality embryos compared to their IVF cycles prior to vaccination. A Hadassah-Hebrew University Medical Center study similarly found the vaccine to have no effect on sperm parameters.
• When all people living in the same house are vaccinated, the chance of any household member contracting COVID-19 is reduced from 57% to 4%, according to a study conducted by Sheba Medical Center in collaboration with the Pasteur Institute and Sorbonne Universit? in France. Even when only one household member was inoculated with the Pfizer vaccine, the risk to unvaccinated household members was reduced significantly. An earlier study indicated that fully vaccinated people seem to be protected from COVID-19 even when exposed to infected family members.
• In early July, the Israeli Health Ministry reported a decrease in the effectiveness of the Pfizer vaccine in preventing infections and symptomatic illness, to 64% from a high of 95% reported in May. This is probably a result of the Delta variant entering Israel. A report released July 22 found the percentage of effectiveness against infections and symptomatic illness had dropped to about 40%, perhaps because the vaccinations given in January and February are wearing off over time. While the early July report found the vaccine 93% effective in preventing serious illness from COVID-19, this number had dropped only to 91% in the late July report. Furthermore, the ministry observed that healthy vaccinated individuals have at least a one-third lower chance of developing severe COVID-19 than do healthy unvaccinated individuals.
• Underlining the above findings, analysis of medical records of tens of thousands of members of Israeli HMO Leumit Health Fund suggests that people vaccinated before late February are now twice as likely to experience a breakthrough SARS-CoV-2 infection than are people vaccinated since late February. It is unknown whether this is because most early vaccinators were elderly and/or had chronic health issues, or because the effect of the Pfizer vaccine may be waning over time. Rare cases of myocarditis, a heart muscle inflammation, have been seen in men under 25 after receiving the second dose of the Pfizer-BioNTech COVID-19 vaccine, a panel of Israeli researchers reported to the Ministry of Health. Most cases were mild and resolved within a few weeks.
• Health Ministry data released in late July indicates that 80% of the vaccinated individuals who experienced breakthrough COVID infections did not infect people with whom they came in contact at public places such as concerts, restaurants, gyms or event halls.
• Israeli studies at the start of the vaccination rollout found that immunity from the Pfizer vaccine was strongest 14 days after the first of two doses. People who got infected after one vaccine dose showed a significantly lower risk of transmitting the virus to others. Furthermore, the first dose boosted immunity even in people who had recovered from COVID-19.
• Employees of Sheba Medical Center who received both doses of the Pfizer vaccine were found to have more antibodies against the SARS-CoV-2 virus than did people who’d recovered from COVID-19.
• A small study at Tel Aviv Sourasky Medical Center found that nursing mothers who were fully vaccinated produced antibodies in their breast milk, potentially protecting their babies.
• A February study showed that people who received the Pfizer vaccination were significantly less likely to “shed” or transmit virus particles that may be in their nose or throat.

By Abigail Klein Leichman/Israel21c