📄 infectious diseases

Inequalities in childhood pneumococcal conjugate vaccine uptake in England before and after the change from a 2+1 to 1+1 schedule: a longitudinal study

This longitudinal study reveals that England's 2020 transition from a 2+1 to a 1+1 pneumococcal conjugate vaccine schedule led to deteriorated booster retention and widened socioeconomic inequalities in vaccine uptake, resulting in a disproportionate increase in susceptibility to invasive pneumococcal disease among children in deprived communities.

Original authors: Ilechukwu, P., Hungerford, D., French, N., Hill, E. M.

Published 2026-01-30

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CC BY 4.0

Original authors: Ilechukwu, P., Hungerford, D., French, N., Hill, E. M.

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine England's childhood vaccination program as a two-step safety net designed to protect children from a dangerous germ called pneumococcus. For years, this net had three strands: two early doses (at 8 and 16 weeks) and a final "top-up" dose at 12 months. This was called the "2+1" schedule.

In January 2020, the government decided to simplify the net. They removed one of the early strands, changing the plan to a "1+1" schedule: just one early dose (at 12 weeks) and the same final top-up at 12 months. The idea was that if the final top-up was given on time, the single early dose would be strong enough to hold the fort.

However, this study acts like a detective, looking at what happened to this safety net between 2013 and 2025. Here is what they found, using simple analogies:

1. The "Top-Up" is Getting Lost

Think of the vaccination schedule like a relay race. The first runner (the early dose) passes the baton to the second runner (the booster dose).

Before 2020: When there were two early runners, the baton usually made it to the finish line. About 91% of children got their final top-up dose.
After 2020: When they switched to one early runner, the baton started getting dropped more often. The number of children who got the final top-up dropped to about 89%.
The Gap: The difference between how many kids got the first shot and how many got the final shot (called the "booster gap") more than doubled. It went from a small 2% gap to a larger 5% gap. It's as if the race became harder to finish, and more children are stopping halfway.

2. The "Rich vs. Poor" Gap is Widening

Imagine the vaccination program as a school bus that picks up children from different neighborhoods.

The Trend: For a long time, children from wealthier neighborhoods were slightly more likely to stay on the bus than children from poorer neighborhoods.
The Change: After the schedule changed, this gap got wider. The children in the most deprived (poorest) areas were the most likely to miss the final top-up dose.
The Result: The study found that the "safety gap" between the richest and poorest areas grew from about 2-3% to 4-6%. It's like the bus is now leaving more children behind in the poorer neighborhoods than before.

3. The "Shield" is Thinner in Some Places

The researchers built a model to estimate how many children are still vulnerable to the disease (susceptible). Think of this as measuring how "leaky" the safety net is.

The Finding: Because fewer children are getting the final top-up, the safety net has more holes in it.
The Inequality: These holes are not spread evenly. They are much bigger in the poorest areas. This means children in disadvantaged communities are at a higher risk of getting sick from the pneumococcus germ compared to children in wealthier areas.
The London Factor: The study noted that London boroughs (city districts) had some of the biggest drops in getting the final dose, making the problem particularly visible there.

4. Why Did This Happen?

The study suggests a few reasons for this "leaky net":

Confusion: When you only get one early shot, parents might think, "I've done the main part," and forget the final top-up is still crucial.
Timing: The schedule change happened right when the COVID-19 pandemic started. The chaos of the pandemic disrupted normal healthcare visits, and the poorest communities were hit hardest by these disruptions.
Hesitancy: Some parents who got the first shot might be confused or hesitant about needing a second one later, especially since the final dose is often given at the same time as the MMR (Measles, Mumps, Rubella) vaccine, which has its own history of controversy.

The Bottom Line

The paper concludes that while the new "1+1" schedule could work, it is currently failing to protect everyone equally because too many children are missing the final dose. The system is struggling to keep up, and the children who need protection the most (those in poorer areas) are the ones most likely to miss out.

The authors suggest that to fix this, the health system needs to be more like a diligent coach: sending better reminders, going directly to the neighborhoods that are struggling, and making sure no child is left behind on the bus. They warn that other countries thinking about similar changes should look at these inequality gaps first, or they might end up with a safety net that has too many holes.

Technical Summary: Inequalities in Childhood Pneumococcal Conjugate Vaccine Uptake in England

Problem Statement
Pneumococcal conjugate vaccines (PCVs) have significantly reduced the burden of invasive pneumococcal disease (IPD) in England since their introduction in 2006. Historically, England utilized a "2+1" schedule (two primary doses at 8 and 16 weeks, plus a booster at 12 months). In January 2020, the schedule transitioned to a "1+1" regimen (a single primary dose at 12 weeks and a booster at 12 months). While immunogenicity studies suggested comparable protection, this reduction in primary doses places greater reliance on the timely uptake of the booster dose to maintain herd immunity and individual protection. Concurrently, childhood vaccination rates in England have declined since 2019, with widening socioeconomic inequalities. This study investigates whether the transition to the 1+1 schedule, occurring alongside the COVID-19 pandemic, exacerbated inequalities in vaccine uptake and increased susceptibility to vaccine-type IPD (VT IPD), particularly in deprived communities.

Methodology
The authors conducted a longitudinal ecological study analyzing quarterly PCV uptake data from 2013 to 2025.

Data Sources: Vaccine uptake data were extracted from the UK Health Security Agency's Cover of Vaccination Evaluated Rapidly (COVER) programme, covering 149 upper-tier local authorities (UTLAs) in England. These data were linked to the 2019 Index of Multiple Deprivation (IMD) to stratify areas into five deprivation quintiles.
Analytical Approach:
- Temporal and Spatial Trends: The study examined national and local trends in primary (12-month) and booster (24-month) coverage, comparing the pre-schedule change period (2+1 era, 2013–2020) with the post-change period (1+1 era, 2020–2025).
- Booster Retention: The "booster gap" was calculated as the percentage point difference between primary coverage at 12 months and booster coverage at 24 months.
- Susceptibility Estimation: A mathematical model estimated the proportion of children susceptible to VT IPD. This calculation combined observed uptake data with published vaccine effectiveness (VE) estimates. The model accounted for unvaccinated children ( $p_0$ ), those with only primary doses ( $p_1$ ), and those fully vaccinated ( $p_2$ ), applying VE estimates for primary and booster doses.
- Sensitivity Analysis: The study tested robustness using different VE assumptions for the 1+1 primary dose (baseline vs. alternate assumptions) and lower/upper bounds of VE estimates.

Key Contributions and Results
The analysis yielded three primary findings regarding the impact of the schedule change and socioeconomic factors:

Deterioration in Booster Retention: Following the transition to the 1+1 schedule, booster retention significantly declined. The mean booster gap increased from 2.32% during the 2+1 period to 4.79% during the 1+1 period. This deterioration was systematic across many local authorities rather than driven by a few outliers. The largest gaps were observed in London boroughs (e.g., Brent, Greenwich, Lewisham), where gaps exceeded 12% in some areas post-2020.
Widening Socioeconomic Inequalities: While a deprivation gradient existed in both periods, the gap between the least and most deprived quintiles widened. Pre-2020, the gap was approximately 2–3%; post-2020, it expanded to 4–6%. The most deprived communities (Quintile 5) and certain middle-deprivation areas (Quintile 3, heavily influenced by London boroughs) showed the slowest recovery and lowest booster coverage.
Increased and Inequitable Susceptibility: Susceptibility calculations revealed a growing proportion of children vulnerable to VT IPD, with significant geographical and socioeconomic variation. Under baseline assumptions, mean population susceptibility rose slightly from 27.1% (2+1 period) to 27.8% (1+1 period). However, the burden was disproportionately concentrated in deprived areas. Sensitivity analyses confirmed that while absolute susceptibility numbers varied with VE assumptions, the pattern of higher vulnerability in deprived quintiles remained consistent.

Significance and Claims
The paper claims that the success of the 1+1 schedule is contingent upon maintaining high, equitable booster uptake, a condition that has not been met in the post-pandemic landscape. The authors argue that the observed decline in booster retention and the widening of socioeconomic gaps threaten the overall effectiveness of the vaccination program.

The study highlights that reducing primary doses without addressing underlying inequalities in healthcare access and vaccine confidence risks concentrating the burden of preventable disease in the most disadvantaged communities. This erosion of coverage not only increases individual risk but may also weaken herd immunity, potentially affecting older, vulnerable populations who rely on community protection.

The authors conclude that other nations considering similar schedule reductions must account for existing inequalities in uptake and booster retention before implementation. They recommend system strengthening, including enhanced call-recall systems, targeted equity-focused interventions in deprived areas, and real-time monitoring of booster gaps as key performance indicators. The paper emphasizes that without these measures, the full protective potential of the 1+1 schedule may not be realized.