The risk of severe COVID-19 in England is extremely rare for completely vaccinated individuals.

A team of UK-based researchers has recently calculated the incidence of vaccine breakthrough infections as well as severe illness in a large number of people who are completely vaccinated against coronavirus infection 2019 (COVID-19) in England. The findings reveal that the majority of vaccine breakthrough cases are mild with only a very small percentage of patients who develop severe COVID-19. The preprint server currently hosts the study.


In December 2020 the UK started a mass vaccination campaign against COVID-19. Initial vaccinations were given to healthcare workers and elderly adults, as well as people at risk and residents of care homes. Afterward, the remaining adults received the vaccination in order of decreasing age. In September 2021, around 75% of people over 16 years old were fully vaccined.

The real-world evidence of vaccine effectiveness has shown that COVID-19 vaccinations have been proven to be extremely efficient in preventing severe acute respiratory syndrome coronavirus 2 infection (SARS-CoV-2), and other serious diseases. However, the rise of vaccine breakthrough cases has highlighted the necessity of finding the risk factors that are that reduce the effectiveness of vaccines.

In the current study, the researchers have determined the frequency of vaccine-related breakthrough cases and COVID-19-related hospitalizations and deaths in a significant number of fully vaccinated people in England.

Study design

The researchers gathered vaccination data from the database OpenSAFELY-TPP, which contains information of around 40 percent of the England population. Total of 10,782,870 people were considered to be fully vaccinated. After 14 days, a person was considered fully vaccination-free. The participants were followed on average for 43 days.

The scientists compared the rates of hospital admissions, breakthrough infections, and deaths among fully vaccinated subjects. The participants were categorized into seven priory groups that included residents of care homes, older adults over 80 years old 70-79 years, 70-79 years, and 50 – 69 years healthcare/frontline workers, clinically highly vulnerable individuals, and other at-risk individuals.

Important observations

About 0.2% of people who had been fully vaccinated were found to have breakout infections. The time required to get a positive SARS/CoV-2 test result was 23 days. For every 1000 years of patient follow-up , the rate of incidence was 12.33. In the various groups of patients, the highest incidence of breakthrough infections was seen in patients who were clinically vulnerable and the less in older adults above 80 years. After 150 days after study initiation, the overall incidence was less than 0.01%.

As we age, the rate of vaccine breakthrough infections decreases. In addition, the rate was significantly higher for females than males, and decreased in White people than those of other ethnic groups.

With a variety of co-morbidities, renal replacement therapy, organ transplantation, hematological malignancy and immunosuppression were all associated with the highest rate of new infections. The highest risk of infection was found within the first 4 weeks following complete vaccination. The risk of infection diminishes with each subsequent week after the last vaccination.

Kaplan-Meir plot of positive SARS-CoV-2 tests over time, by priority group

Hospitalization for severe COVID-19

About 0.01% of people who had been fully vaccinated were admitted to hospitals due to COVID-19. The average hospitalization was 33 days. In the hospitalized patients, around 73% had a positive SARS-CoV-2 test result in their medical records. Of these that occurred, 25% occurred prior to admission to the hospital 21% were detected within two days of admission, 38% happened between 3 and 29 days after admission and 16% were discovered after 30 days after admission.

With age, there was an increase in hospitalization rates. The risk was 3-fold higher for Asian and Asian British people compared to White individuals. The risk of hospitalization was also higher for those who were economically disadvantaged.

Hospitalization rates are also impacted by comorbidities that are associated with an increase in the infection rate. After full vaccination, the lowest rate of hospitalization was reported within four weeks. The rate has been increasing slowly over the time since the last vaccine.

Hospitalization due to severe COVID-19

The mortality rate of fully vaccinated individuals was much less than 0.01 percent. The average time to die was 40 days. Senior people over 80 who live in care homes had the highest mortality rates. The number of deaths among people aged under 60 years was nil. The mortality rate in the West Midlands was 5 times greater than that of the South West.

Hematological malignancy, kidney disease, and organ transplant were the most common co-morbidities. Patients suffering from respiratory diseases and immunocompromised patients were at greater risk of COVID-19-related deaths.

The significance of the study

Study results show that mild infections are the most frequent reason for breakthroughs in vaccines in England. Only a small percentage of people who have been fully vaccinated develop serious or fatal COVID-19.

Journal reference:

Content Source:

Gemma Wilson

Gemma is a journalism graduate with keen interest in covering business news – specifically startups. She has as a keen eye for technologies and has predicted quite a few successful startups over the last couple of years.

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