JERUSALEM (BLOOMBERG) - Israel, with the highest proportion of citizens vaccinated against Covid-19 in the world, found it took three weeks for the Pfizer Inc-BioNTech SE shot to start curbing new cases and hospitalisations.
Researchers in the Middle Eastern country reported preliminary observations Wednesday (Feb 3) from a national immunisation programme that began Dec 20.
Improvement in the number of new cases and hospitalised patients occurred 21 days following the vaccination campaign, the scientists said, noting that the real-life effect of vaccines may take longer than what was demonstrated in clinical trials.
"To our knowledge, no study thus far has studied the impact of the vaccination campaign on the population level and its effect on the patterns of pandemic dynamics," scientists from the Weizmann Institute of Science in Rehovot said. "As Israel is one of the first countries to implement a vaccination campaign on this magnitude, we believe that this quantification may be of major interest for many countries worldwide."
Israel's vaccination drive began just before a more transmissible Sars-CoV-2 strain emerged, fuelling infections and leading to a third lockdown on Jan 8.
As of Tuesday, 28 per cent of Israelis - including three-quarters of those 60 years or older - had either received two doses of the vaccine or had recovered from an infection. At the peak, 229,508 doses were administered in one day.
Efforts to estimate the true real-world effectiveness of the vaccine have been hampered by disease dynamics and social-economic discrepancies, according to Dr Dvir Aran, an assistant professor in the biology department at Technion-Israel Institute of Technology in Haifa.
Using tallies of cases and hospitalised patients among vaccinated individuals, Dr Aran found the shot was 66 per cent to 85 per cent effective in reducing the number of Sars-CoV-2 positive cases and was more than 90 per cent effective in reducing severe hospitalisations, he said Friday in a separate paper, published before peer-review and publication.
"There is little doubt that the vaccine is highly effective in reducing cases, hospitalisations and deaths," Dr Aran concluded.
Efficacy might differ slightly from the clinical test data in real-life settings for several reasons, the Weizmann researchers said. Logistics, including the refrigeration, storage, transportation and administration of the vaccines during a rapid rollout may be imperfect, lowering effectiveness, they said.
The US Centres for Disease Control and Prevention recommends the Pfizer-BioNTech vaccine be stored at -80 deg C to -60 deg C.
The researchers also noted that older people - who were prioritised earlier in Israel's vaccination campaign - potentially had a reduced or delayed response to vaccination due to age-related deterioration in their immune function.
Infectious variant
It's also possible that the efficacy of the vaccine is reduced in the face of some of the emerging virus strains, including the B117 variant discovered in the UK that's now prevalent in Israel, and the 501YV2 first observed in South Africa, the researchers said.
They also noted that vaccinated individuals may alter their behaviour and decrease adherence to public health prevention guidance, such as physical distancing and wearing face masks, thereby increasing viral transmission.
"Moreover, viral transmission may also occur in the vaccination areas themselves," the researchers said. "The vaccination sites should be large and ventilated in order to decrease the probability of transmission on site."
Parts of Israel with higher infection rates and a lower socioeconomic status had lower uptake even with adequate vaccination availability, the researchers found, noting a need to encourage citizens in these areas and to make shots even more accessible there.
The researchers concluded that more studies aimed at assessing the effectiveness of vaccination on reducing the transmission of Sars-CoV-2 are needed both on the individual and on the population level with larger follow-up and in additional populations.
