The second booster, i.e. the fourth tranche of the vaccine of Pfizer/BioNTech further reduces - compared to the third dose - the likelihood that people over 60 years of age will be infected with coronavirus and get sick because of Covid-19. But protection against at least the possibility of infection seems short-lived, according to a major new Israeli scientific study, which looks at the prevalence period of the Omicron variant of the coronavirus (January-March 2022). Instead, the increased protection against the severe disease seems to last longer - for an unknown amount of time.
The researchers, who analysed data on about 1.25 million people over 60 and published the study in the American medical journal “The New England Journal of Medicine”, according to Reuters and the New York Times, reported that the protection of the fourth dose against infection appeared to peak in the fourth week, then to decrease and almost disappear by the eighth week.
On the other hand, protection against severe disease does not decrease during the first six weeks after the fourth dose. The likelihood of severe disease was 3.5 times higher for those who had three doses than for those who had four, while six weeks later it was 4.3 times higher. The study did not include comparative data on deaths, and it is not clear how long the protection against severe Covid-19 disease lasts, as further study will be needed.
The findings, according to the scientists, support the view that the additional doses of vaccine provide increased but temporary protection against Omicron and that the efficacy of the fourth dose decreases more rapidly against the likelihood of infection than against the risk of severe disease.
An earlier Israeli study in March showed that elderly people who took a fourth Pfizer/BioNTech dose had 78% less mortality than those who had taken three doses. Israel began administering a fourth dose of the vaccine to those over 60 years of age as of January 2, 2022.
The new data comes amid debate - and disagreement - in the US and Europe over the fourth tranche, when to give it and to whom. In March, the US Food and Drug Administration (FDA) approved giving a fourth dose to those over 50 years old and immunocompromised people over 12 years old at least four months after the third dose, as well as giving a booster third dose to those who have had two doses of Johnson & Johnson's mono vaccine.
The director of the US Centers for Disease Control and Prevention (CDC) said it “really encourages people over 50 years old with underlying medical problems and those over 65 years old to get a second booster dose”. In the EU, health ministers are generally in favour of a fourth dose in the over-60s.
