Vaccine efficacy is lower with the Omicron variant, but increases with booster dose

Explanation was given by Ana Paula Rodrigues, from the National Institute of Health Doctor Ricardo Jorge (INSA)

The effectiveness of the vaccine against Covid-19 is lower in the Omicron variant than estimated for Delta, but after the booster dose it increases and varies depending on the vaccine and the time since the last dose, according to experts.

In her presentation today at the meeting of Infarmed experts, Ana Paula Rodrigues, from the National Institute of Health Doctor Ricardo Jorge (INSA), explained, citing several studies, that the effectiveness of the vaccine against infection in the case of the Ómicron variant lies between 40% to 70% and is considered “moderate against symptomatic infection”.

The specialist also said that immunity drops more quickly in the Omicron variant than what was seen in Delta, due to the greater ability to escape the immune system.

The efficacy against hospitalization, regardless of the type of vaccine, in the case of Ómicron, and after the vaccine booster, is 88%. After the second dose, it is between 52% and 72%, «depending on the time that elapsed between the last dose of the vaccine», said Ana Paula Rodrigues.

The data point to lower values ​​in the effectiveness of the vaccine compared to what was seen in the Delta variant, “but after the boost it gets closer. However, it is not known yet what is the decrease in the risk of hospitalization over time, but it is expected that it will be smaller”, he added.

During the presentation she made about the seriousness of the infection, the effectiveness of the vaccination and the expected impact, Ana Paula Rodrigues also said that taking into account that in the age group between 50 and 59 years, 70% still do not have a vaccine booster for this group. "should be extra careful in the measures of individual protection".

He also underlined that, despite the lesser effectiveness of vaccines, a high burden of disease is expected, but with a lower severity, as "there are several signs of less seriousness in Omicron infection".

"It is more benign than what we had before", considered the specialist, insisting that "individual protection measures are justified, regardless of age, as well as the reinforcement of the vaccine and the continuity of vaccination in the current target groups".

Before Ana Paula Rodrigues, João Paulo Gomes, also from INSA, explained why the severity of disease with the Omicron variant is lower, despite the greater transmission capacity, noting that this variant has more mutations in the cell-binding zone human beings, hence it escapes more from the immune system and spreads more easily, but it has less capacity to replicate in the lungs due to the «low affinity for specific proteins in the lungs».

Citing experimental data from the University of Hong Kong, the expert indicated that, in the case of the Omicron variant, the replication process in the upper airways is 70 times faster than in the Delta variant, but 10 times slower in the lower lung cells, the which explains the lower severity of the disease.

He also added that "there is no significant difference between those infected with Omicron and Delta in terms of viral load".

João Paulo Gomes also said that Ómicron already represents 90% of infections in Portugal and pointed out the «great heterogeneity, both in timings as in the spread in the various regions», giving the example of the Algarve, which in Christmas week still had a 40% share of one of the strains of the delta variant, “imported” from the United Kingdom and linked to tourism.