Many Won¡¯t Need A 4th COVID-19 Jab As They¡¯re Hitting A Vaccine Ceiling: Here¡¯s What It Means

Researchers have hinted that some individuals who have already received three jabs of the novel coronavirus vaccine could be approaching a vaccine ceiling, indicating that they won¡¯t need a fourth jab against COVID-19.

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This is according to a new study conducted by the University of Southampton (reported first by The Independent) that assessed the protection levels of over 150 people before and after vaccination.

The study

Researchers also looked at people who had two doses of the AstraZeneca vaccine, followed by a Pfizer booster who then either received a Modena or Pfizer vaccine for their fourth jab.

They also looked at people who had three doses of Pfizer followed by a fourth Pfizer shot or a half Modena jab. No one experienced any severe side effects, apart from pain or fatigue.

Blood samples were collected and examined for antibody levels at various time points -- 28 days after the third jab, just before the fourth booster was administered (around 200 days later) and then 14 days after they had their fourth jab.

The ¡®vaccine-ceiling effect

For several participants, their antibody count in the period between the third and fourth dose was waning. However, 14 days after the booster jab saw the levels rise to new heights, over and above what was previously recorded.

In fact, some had 12 to 16 times higher levels of antibodies in the blood for 14 days after their fourth shot, compared with the day it was delivered.

There were also some participants who maintained high levels of humoral and cellular responses even before the fourth dose and saw limited boosting from the fourth dose, hitting a vaccine-specific ceiling effect.

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What could be responsible for it?

Professor Saul Faust, the leading scientist of the CovBoost trial, stated that this would be based on the type of vaccines, previous dosage volumes, as well as immunity levels developed due to vaccination and natural infection.

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He explains, ¡°There¡¯s a hint from some of the people in the trial and some of the people in the trial who had had Covid ¡­ that vaccines might reach a ceiling and that will depend on the vaccine and the host immunity and the dose, and that is true for the over-70s and the under-70s.¡±

According to him, a fourth dose might not ¡®boost humoral and cellular responses if the baseline response is already high.

He added, ¡°These individual data are important for policymakers as the benefit of a fourth dose might be less in people who already have high levels of immune responses from recent infection or vaccination.¡±

Scientists call for the ¡®vaccine ceiling effect¡¯ to be further explored with the help of newer studies.

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