Covid-19 vaccine booster shots: what do we know so far?
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Covid-19 vaccine booster shots: what do we know so far?

By Darcy Jimenez 25 Aug 2021 (Last Updated September 14th, 2021 11:50)

The US is recommending booster shots of Pfizer and Moderna jabs in response to evidence that protection against Covid-19 is waning.

Covid-19 vaccine booster shots: what do we know so far?
US health officials say “boosters will likely be needed” for individuals who received Johnson & Johnson’s one-shot vaccine. Credit: Shutterstock.com

In August, US officials announced that from September, double-vaccinated adults aged 18 and older would be offered Covid-19 vaccine booster shots, pending data to confirm the safety and efficacy of a third dose of either the Pfizer or Moderna jab.

The decision was made in response to evidence that protection against coronavirus is decreasing, which public health officials noted is likely due to “both waning immunity and the strength of the widespread Delta variant”.

Booster shots: what’s the evidence?

While data shows that two vaccine shots are largely effective at protecting against severe Covid-19, data on the benefit of booster shots is currently unclear. To establish whether a booster dose would offer significantly increased protection, experts first need to understand the level of antibodies and other immune defences needed to prevent severe illness and death from Covid-19. Once this has been measured, and immunity is seen dropping to this level, a case for routinely administering booster shots can be made.

A recent Israeli study found a third dose of Pfizer’s vaccine to be 86% effective in people aged over 60, and a UK trial assessing whether a third shot of different Covid-19 vaccines could boost immunity against the virus is ongoing, with results expected in September.

Preliminary data from an Oxford University-led study evaluating the AstraZeneca vaccine has also found that third dose of the jab boosts antibodies against Covid-19.

What are countries’ plans for booster shots?

At this time, the US Centers for Disease Control (CDC) only recommends booster vaccine doses for those who are moderately to severely immunocompromised.

Provided the Food and Drug Administration (FDA) and CDC give the US’s September plan the green light, Americans will receive third doses of either the Pfizer or Moderna mRNA vaccines. Pfizer and BioNTech last week submitted initial data to the FDA to support the approval of a booster dose of the companies’ vaccine.

US health officials say “boosters will likely be needed” for individuals who received Johnson & Johnson’s one-shot vaccine, but a plan for these jab recipients will be made once more data is available.

The UK health regulator has approved the AstraZeneca and Pfizer vaccines as safe and effective for third shots, and the Joint Committee on Vaccination and Immunisation (JCVI) has recommended that boosters should be offered to all over-50s and people at severe risk of illness from Covid-19.

Health secretary Sajid Javid previously announced that a vaccine booster scheme is likely to commence in September. Javid said the exact date will be announced following final advice from the JCVI, but that the most at-risk populations will be offered third doses first.

Israel has already kicked off a booster shot programme for older members of the population, while both France and Germany plan to offer third doses to the elderly and vulnerable from September.

The World Health Organization, however, has said booster vaccination schemes will “exacerbate inequities by driving up demand and consuming scarce supply”. Introducing third vaccine doses should be “firmly evidence-driven and targeted to the population groups in greatest need”, the organisation said.