Omicron variant, third dose Pfizer raises the shield

First two doses protect up to 70%

Third dose of Pfizer raises the defense against the Omicron variant. Already with two doses the protection should be at 70% according to a study, conducted on ‘real world’ data from South Africa. Two other papers, not yet published and therefore not peer-reviewed, also observe the impact of the third dose, showing after the booster an increase in the ability to neutralize Omicron compared to double dose, albeit at lower levels than those found against Delta.

In one of these two studies, an Israeli research available on the ‘Medrxiv’ platform, the authors used isolates of different variants including Omicron to study the neutralization capacity of the Pfizer / BioNTech vaccine. Experts demonstrate “the importance of the third dose”, since after the booster they detect a “100-fold increase in neutralization efficiency” towards the Omicron variant. But this neutralization is “reduced by 4 times” compared to that obtained against Delta. The duration of the effect is yet to be determined. The authors also note “a low neutralization efficiency against Delta and the wild-type virus” after more than 5 months from the second dose, “without any neutralization efficiency against Omicron”.

The results of the second study, which instead comes from Australia and is available on the ‘Biorxiv’ platform, are also online. The sera collected one, 3 and 6 months after two doses of Pfizer / BioNTech showed also in this case “a limited capacity to neutralize” the virus. However, the authors continue, “4 weeks after the third dose, neutralizing antibody titers are enhanced. Despite this increase, neutralizing antibody titers are reduced 4-fold for Omicron.”

To trace a picture of the shield effect of the two doses is a work conducted by Discovery Health, the largest health insurer in South Africa, on 211 thousand positive cases, of which 78 thousand attributed to Omicron. The analysis, bounced in the international press, showed a protection against hospitalization from Omicron that is described by the authors of the work as still “very good”. Furthermore, the risk of hospitalization among adults with Covid was 29% lower than the initial pandemic wave. However, the study also found that the vaccine appears to have provided only 33% protection against infection, far less than the level achieved compared to other variants in the country.

The data from South Africa, Ryan Noach, Chief Executive of ‘Discovery Health’ told a news conference, “shows an exponential increase in both new infections and test positive rates during the first 3 weeks of this wave,” elements that appear suggest that Omicron is “a highly transmissible variant with rapid community diffusion”. But, Noach added, “what is encouraging at this stage is the flatter trajectory of hospital admissions, probably indicating a lower severity of this wave.”