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15th February 2023
According to the findings of a systematic review in the Lancet, COVID-19 vaccine effectiveness wanes over time, even following booster doses, indicating that in the longer-term, it may be necessary to continue with preventative measures such as face-mask wearing and physical distancing to help manage the pandemic.
While the introduction of COVID-19 vaccines had an enormous impact on hospitalisations and mortality due to infection with the virus, it has been recognised that induced antibody levels reduce over time. A previous systematic review in 2022 observed that while vaccine efficacy against severe disease only dropped by 10% from one to six months, it reduced by approximately 21% against infection after 6 months and by nearly 25% against symptomatic illness. However, the analysis did not consider the impact of COVID-19 booster doses. As a result, in the current study, researchers examined the effectiveness of vaccination against infection, hospitalisation and death among those who had received a booster dose.
The team examined studies that provided data on vaccine effectiveness for at least 112 days after the primary series of vaccinations or at least 84 days after receipt of a booster dose. They set the primary outcomes of interest as effectiveness against COVID-19 infection, hospitalisation and mortality.
Vaccine effectiveness against COVID-19 outcomes
A total of 68 studies were included in the final analysis.
Overall effectiveness against any strain of COVID-19 reduced from 83% after a primary series of vaccinations to 62% by 112 to 139 days. Similarly, baseline effectiveness against hospitalisation was initially high at 92% but dropped to 79% after 168 – 195 days, as did effectiveness against mortality (91% to 86%) over the same period of time.
Among those who had received booster doses and for which most studies included the omicron variant, vaccine effectiveness against infection was initially 70% but reduced to 43% after 112 days. Similarly, boosted doses against hospitalisation reduced from a baseline of 89% to 71% over the same period of time. The authors reported that there was insufficient data to assess the impact on mortality.
Commenting on their findings, the authors suggested that maintaining COVID-19 prevention behaviours including the wearing of face-masks and physical distancing as well as vaccination may be necessary to reduce transmission of the virus, given how immunity wanes over time. They called for future studies to investigate the effectiveness of simultaneously using multiple approaches such as vaccination and face-masks as transmission preventative strategies.
Wu N et al. Long-term effectiveness of COVID-19 vaccines against infections, hospitalisations, and mortality in adults: findings from a rapid living systematic evidence synthesis and meta-analysis up to December, 2022. Lancet Respir Med 2023
16th August 2022
According to a press release from the MHRA, an updated version of the COVID-19 vaccine made by Moderna and which targets two coronavirus variants (known as a “bivalent” vaccine) has now been approved for use as a booster dose for adults in the UK.
In each dose of the updated vaccine, ‘Spikevax bivalent Original/Omicron’, half of the vaccine targets the original COVID-19 strain from 2020 and the other half (25 micrograms) targets Omicron. The current MHRA approval was based on the findings of a phase 2/3 trial, which is available as a pre-print in which the bivalent vaccine was compared to the authorised 50-µg mRNA-1273 booster in adults who previously received 2-dose primary series of 100-µg mRNA-1273.
Earlier work with the bivalent COVID-19 vaccine had shown that it elicited a higher neutralising antibody response against the ancestral (or original) COVID-19 and the Beta variant than that after the second mRNA‑1273 dose (i.e., the original Moderna vaccine), as well as against the Omicron and Delta variants.
Clinical efficacy of the Bivalent COVID-19 booster
In the latest pre-print study, the bivalent COVID-19 booster was examined in a group of 437 individuals with a mean age of 57.3 years (41% male) and compared with a group of 377 patients (mean age, 57.5 years, 49.3% male), who received the mRNA-1273 (50 µg) vaccine.
The interim analysis is based on data 28 days after the booster vaccine doses. The results showed that the bivalent COVID-19 booster dose neutralising geometric mean titres (GMT) against Omicron were 2372.4 compared to 1473.5 for the mRNA-1273.
Additionally, the bivalent COVID-19 booster induced a more potent neutralising antibody response against omicron sub-variants BA.4/BA.5 and and higher binding antibody responses against alpha, beta, gamma, delta and omicron variants.
The authors of the pre-print concluded that the bivalent booster elicited a superior neutralising antibody response against omicron, compared to mRNA-1273, and potent neutralising antibody responses against the BA.4 and BA.5 omicron sub-variants, 28 days after immunisation.
Commenting on the approval, Dr June Crown, the MHRA chief executive said: ‘The first generation of COVID-19 vaccines being used in the UK continue to provide important protection against the disease and save lives. What this bivalent vaccine gives us is a sharpened tool in our armoury to help protect us against this disease as the virus continues to evolve.’