A few days ago, Israeli official agencies and British official agencies respectively published the latest research results on the effectiveness of Pfizer vaccine in their country: The Israeli Ministry of Health pointed out that the vaccine is only effective in preventing infection with the new coronavirus “Delta” (δ) strain. 39%, the effectiveness of preventing symptomatic infections is about 40%; almost at the same time, researchers from the National Institutes of Health, Oxford University and other researchers published in the “New England Journal of Medicine” that the Pfizer vaccine is effective in preventing the delta strain. The effectiveness of symptomatic infections is as high as 88%.
The difference between 40% and 88% is more than doubled. Why is the performance of the same vaccine so different in different countries? In this regard, Professor Cyril Cohen, a member of the Advisory Committee of the New Crown Vaccine Clinical Trial of the Israeli Ministry of Health, gave the following explanation in an interview with the “Jerusalem Post”:
First, the time of vaccination is different. The British vaccinations are late, and the immunity is not severely weakened, so the effectiveness is higher. It was not until the beginning of July that half of the population was vaccinated in the UK, more than three months later than Israel. Studies have shown that the immune effect of the vaccine is significantly weakened after 6 months, and the protection rate of Pfizer vaccine for the population vaccinated in January this year is only 16%. According to the Ministry of Health, from July 11 to 17, among the 1.8 million people who completed vaccination before January 31, as many as 1,181 were infected, accounting for 20% of new infections.
The second is that the vaccinated population is different. In the UK, the main audience of Pfizer vaccines is people under the age of 40, and the elderly are mainly vaccinated with AstraZeneca vaccine. In Israel, Pfizer vaccine is widely vaccinated among people of different ages. People over 60 years of age have poor immunity, and the protective effect of the vaccine is more attenuated. The immune barrier established by the vaccine is more likely to be broken by the delta strain, and symptoms are more likely to occur after being infected by the virus. Therefore, this is one of the important reasons why Pfizer vaccines seem to be less effective in Israel.
Third, the level of virus detection is different. Israel uses a more sensitive and rigorous PCR test than the UK. The genetic material of the virus is amplified by PCR test cycles. The more cycles run, the more likely the laboratory will detect the virus. Israel uses 37 amplification cycles with high detection sensitivity. Cohen said Britain may miss some cases, or Israel may find more cases.
In addition, another reason may be the different vaccination methods. Israel strictly implements the immunization program with an interval of 3 to 4 weeks between the first dose and the second dose of vaccination, while the United Kingdom has extended the interval between the second dose to 4 to 12 weeks in order to increase the number of people receiving at least one dose of the vaccine. Recent studies have shown that the second dose of vaccine in 6 to 14 weeks produces higher levels of neutralizing antibodies than in 3 to 4 weeks. However, Cohen does not agree with this practice of extending the vaccination time during the pandemic. He said that a dose of Pfizer vaccine is only about 30% effective, which will leave the population in a vulnerable state for a long time.
