COVID-19: Decoding the dwindling efficacy of Pfizer’s vaccine

Data from the Israeli health ministry released recently has showed that the efficacy of the Pfizer-BioNTech vaccine against COVID-19 had shown a significant drop in recent weeks. The efficacy of two shots in preventing symptomatic infection were found to be only 64% against 94% earlier this year. However, the vaccine remains 93% effective in stopping hospitalisation, albeit slightly lower than 97% earlier.

The new data comes on the back of a research by Hebrew University, which found that the vaccine was 70% effective against the dominant Delta variant, reportedly responsible for more than 90% of the recent cases in Israel. The country has already vaccinated 57% of its entire population and lifted restrictions in June.

A study in The Lancet last month had found that a dose was only 32% effective against the Delta variant, compared with 79% against the original strain. The level of neutralising antibodies generated even after two doses was more than five times lower against the Delta variant than that against the original strain. Other studies, including one conducted in June by Public Health England, corroborate the findings that the Pfizer vaccine offered a high level of protection from hospitalisation, even against the Delta variant.

The data from Israel is based only on “preliminary” figures that were gathered between June 6 and early July. Ran Balicer, chair of the country’s national expert panel on COVID-19, , said it was too early to assess precisely the vaccine’s efficacy against the Delta variant. Pfizer spokesperson Dervila Keane reportedly said so far, their evidence suggested the vaccine would continue to protect against the variants.

Israel now plans to conduct a detailed study of vaccinated people in an attempt to assess the vaccine’s efficacy. Pfizer CEO Albert Bourla has already said people might need to get a third shot within 12 months of the second.