Delaying second Covid jab ‘saved thousands of lives’

The decision in early 2021 to delay people’s second Covid-19 jabs caused huge controversy, but research has now found that this saved thousands of lives.

At the time, many questioned why the government and Joint Committee on Vaccination and Immunisation was apparently going against the original clinical guidance. However, research from Imperial College has now suggested that decision was in fact an excellent call, as it potentially prevented tens of thousands of hospitalisations and thousands of deaths in England.

The findings come from a retrospective analysis from the Imperial College London Covid-19 Response Team, which aimed to quantify the impact of delaying the delivery of second vaccine doses on the epidemic in England.

Its analysis has estimated the decision may have prevented an average of 58,000 hospital admissions and 10,000 deaths between 8 December 2020 and 13 September 2021.

This was because extending the interval between the first and second doses of Covid-19 vaccine from three to 12 weeks enabled a greater number of people to receive a first dose and thereby gain partial protection.

This included younger age groups who were less vulnerable to severe disease, but who contributed more to transmission. Therefore, vaccinating them early indirectly protected the most vulnerable groups, the researchers argued.

As vaccine-induced protection wanes over time, the 12-week strategy had the added benefit of maintaining a higher population-level immunity during the Delta wave in summer 2021, they also found.

The findings, from researchers at the MRC Centre for Global Infectious Disease Analysis and Jameel Institute at Imperial, have been published in journal The Lancet Public Health.

The UK government began its rollout of Covid-19 vaccines in December 2020, with the initial guidance being that the first and second doses should be administered three weeks apart in line with clinical trial protocols.

However, following real-world evidence that a single dose of vaccine was effective and the emergence of the more transmissible Alpha variant over the 2020/21 winter, that policy was changed.

Dr Anne Cori, from the MRC Centre for Global Infectious Disease Analysis at Imperial and senior author on the paper, said: “Our analysis finds that in England, the early switch to a 12-week vaccine dose interval saved thousands of lives and prevented tens of thousands of hospitalisations from Covid-19, highlighting the benefits of being able to react swiftly as new data become available.

“This study demonstrates the value of mathematical models, calibrated to detailed epidemic data, to investigate control options not only prospectively, as our team has done continuously since early 2020, but also retrospectively,” she added.

Using a previously established model, the researchers used available data from the Department of Health and Social Care to estimate the transmission rates and model infections, hospital admissions and deaths in the population in England from the start of the vaccine rollout to just before the start of the booster campaign, in other words from December 2020 through to September 2021.

They estimated that following the original three-week interval strategy would have resulted in many more hospital admissions and deaths compared to the 12-week strategy.

Under the three-week strategy, there were a higher number of daily hospitalisations, peaking at an estimated 2,030 people hospitalised with Covid-19 on July 22, 2021.

Over the entire study period, the three-week strategy resulted in an estimated cumulative 291,000 hospitalisations and 64,800 deaths from Covid-19, compared with 233,000 hospitalisations and 54,700 deaths under the 12-week strategy.

Dr Natsuko Imai, honorary senior research fellow within the MRC Centre for Global Infectious Disease Analysis, and joint first author on the paper, said: “For the public, it can be confusing when policy seems to change frequently.

“But analyses like ours show the importance of being able to adapt health guidance when informed by new evidence and that continuous surveillance and reassessment is crucial to making informed decisions during health crises.”