A new study is shedding light on the benefits of getting a fourth COVID-19 vaccine dose or a second booster amid the ongoing pandemic. The findings may strengthen the public’s trust as the medical community continues to figure out a long-term solution for the novel coronavirus.

The team behind the research aimed to investigate the reactogenicity and immunogenicity of the fourth dose on top of its safety, with a focus on individuals previously jabbed with Pfizer and AstraZeneca vaccines and received the Pfizer vaccine as their booster. A total of 166 people participated in the UK-based Cov-Boost trial. Half of them were given a full dose of the Pfizer vaccine as their fourth dose, while the remainder got half a dose of the Moderna vaccine.

After collecting data from the participants, the team analyzed the reports from 133 participants 14 days after receiving their fourth jab. Researchers found a 1.6-fold increase in antibodies among participants who received the full dose of the Pfizer vaccine and a twofold increase among those who were given the half-dose Moderna vaccine. The figures were derived from a comparison with the antibody levels of their first booster (third dose) at their peak.

“Fourth-dose COVID-19 mRNA booster vaccines are well tolerated and boost cellular and humoral immunity. Peak responses after the fourth dose were similar to and possibly better than, peak responses after the third dose,” the team wrote in their study published in The Lancet Infectious Diseases on Monday.

National Institute for Health Research (NIHR) Southampton clinical research facility director Prof Saul Faust, who led the trial, admitted that based on their analysis, the fourth dose of the COVID-19 vaccines did provide “a substantial boost” to the immunity of the participants from the virus. However, he acknowledged that timing plays a big part in this.

“We’ve demonstrated a fourth dose of Covid-19 vaccines can produce a substantial boost to both the antibody and cellular immunity when you give them more than six months after the third dose,” Faust told The Guardian.

The antibody boost was evident in participants over and below 70 years of age. The antibody and T-cell levels also substantially increased between a day before the fourth dose and 14 days after the second boosters were administered.

Faust pointed out that those who recorded only a minute dip in their immune responses before the fourth dose gained a limited boost in antibody levels. The same was observed in participants who had a recent COVID-19 infection before receiving the second booster.

There is an ongoing debate on whether or not everyone should be given the fourth dose and not just the middle-aged and immunocompromised. For Imperial College London immunologist Prof Danny Altmann, the findings of the study demonstrated the added value of a fourth dose amid the ongoing pandemic.

“Just because our first-generation vaccines wane rapidly and offer rather permeable protection nowadays, does not suggest we should give up and have no further boosters. On the contrary, [given] many of us, even with high apparent antibody levels, actually show [very little] protective neutralization of omicron, there is all the more urgency to use [fourth] doses – in all age groups – to boost levels back up into the protective range,” Altmann said.