Google+ Facebook Twitter Twitter

Jabs and long Covid

Vaccines reduce the odds of SARS-CoV-2 infection, but also long COVID, says Dr Rose Penfold, discussing her new study.

Vaccinating populations worldwide against SARS-CoV-2 is a pivotal strategy to change the course of the COVID-19 pandemic and reduce mortality. Since the first vaccines were approved in late 2020, there has been hope that the spread of the virus would soon be controlled.

This has proved more challenging to achieve than expected, due to the emergence of more contagious variants and the rise of anti-vaccination movements weakening the success of vaccination campaigns. Furthermore, while COVID-19 vaccines show very good efficacy in clinical trials and effectiveness in real-world data, some people are still infected, even though they have been vaccinated. But there’s cause for optimism.

The study

In a recent study published in The Lancet Infectious Diseases, scientists have shown that vaccination not only reduces the odds of contracting SARS-CoV-2 infection, but also hospitalisation, as well as symptoms associated with more severe disease. For the first time, the data also suggest that vaccines are effective in reducing the risk of long-duration symptoms, often referred to as “long COVID”, as co-author Dr Rose Penfold tells us.

This prospective, case–control study was based on self-reported data from UK-based users of the COVID Symptom Study mobile app. When people first register on the app, they are asked to fill in details regarding their demographics (age, sex, ethnicity, weight, height, and health-care worker status), geographical location and health risk factors. After this first step, they are regularly prompted to answer questions via the app on their health and symptoms, and to give information on COVID-19 test results and vaccination status.

“Using this data, we aimed to identify risk factors for post-vaccination SARS-CoV-2 infection and describe the characteristics of post-vaccination illness. What factors confer an increased risk of SARS-Cov-2 infection, even after first or second vaccination? In those individuals who are infected after vaccination, what’s the difference in disease severity? These are the questions we were hoping to answer,” says Penfold. 

The researchers analysed data from over 8000 participants to look at risk factors for post-vaccination infection. Two groups of cases were selected. The first included people who had received a first or second dose of vaccine after 8 December 2020 and a positive COVID-19 test at least 14 days after their first vaccination (but before their second).The second included vaccinated individuals who had reported a positive test at least seven days after their second dose. These groups were matched to two control groups of vaccinated adults – one with people who had reported a negative test result at least 14 days after the first dose and the other with people with a negative test result at least seven days after their second dose. No participant had a positive test before vaccination.

The authors again selected two control groups. The first included people who had received a first or second dose of vaccine after 8 December 2020 and a positive COVID-19 test at least 14 days after their first vaccination (but before their second), while the second included vaccinated individuals who had reported a positive test at least seven days after their second dose. These groups were matched to two control groups of unvaccinated adults contemporaneously reporting a positive COVID-19 test.


When it comes to preventing infection,the data suggest that vaccination is highly effective, especially after two doses. “Although we are unable to tell with what variant our participants had been infected, and these numbers may have varied a little if we had only focused on the delta variant, our study period does overlap with the period when delta became the dominant UK variant. This suggests that findings remain highly relevant”, Penfold says.

People who did get infected following vaccination were less likely to get severely ill. Indeed, the study found that almost all individual symptoms of COVID-19 (such as fever, dry cough and tiredness) were less common in vaccinated versus unvaccinated participants, and more people in the vaccinated than in the unvaccinated groups were completely asymptomatic. Disease was less severe, with a lesser number of symptoms and a reduced risk of needing hospitalisation in vaccinated individuals compared with unvaccinated individuals.

But this study goes one step further. It also demonstrates that the odds of having symptoms for 28 days or more after infection – what is often referred to as long COVID – were approximately halved by having two vaccine doses. “Our study is the first to suggest that the risk of long COVID is reduced in individuals who have received double vaccination. This is an important argument to convince young people and those generally less at risk of getting severe COVID-19 that vaccination is beneficial,” Penfold says.

Dr Rose Penfold
  • Academic Clinical Fellow in Geriatric Medicine working clinically as a doctor at Guy’s and St Thomas’ Hospital.
  • Currently undertaking research with the COVID Symptom Study team at King’s College London, United Kingdom.
  • Interests include cognition and frailty. She has been able to apply clinical insights as second author on this paper on risk factors and illness profile of post-vaccination SARS-CoV-2 infection.

Targeted public health policies

The researchers also studied risk factors for reporting a positive COVID-19 test after vaccination. In line with previous studies showing that people in more socio-economically deprived areas – with higher density and more ethnic diversity – are more vulnerable to infection and COVID-19 mortality, this research suggests that greater area-level deprivation is associated with increased odds of SARS-CoV-2 infection after a single vaccine dose. One hypothesis is that these areas might have lower vaccination coverage overall, with increased viral transmission.

“These findings highlight the need to come up with health policies specifically targeting those at greater risk of post-vaccination infection. The findings are also relevant as we move into the post-vaccination era, when thinking about enhancing immunogenicity in individuals more at risk,” Penfold explains.

“The risk of long COVID is reduced in individuals who have received double vaccination”

Another important risk factor for infection, after one and two doses of vaccine, was frailty, which can be defined as a common clinical syndrome in older adults who carry an increased risk for poor health outcomes, including falls, incident disability, hospitalisation, and mortality.  Frail older adults were at higher risk of infection after vaccination, perhaps because of altered immune function, which may prevent them from responding fully to vaccines or as a result of increased exposure to the virus, during carer visits or attendance at healthcare facilities. “With much of the public debate focused on whether a third booster dose might be beneficial, our study is important to help identify who is more vulnerable and to target at-risk populations,” Penfold concludes.

The team will now work with data collected through the app to continue looking at the immediate impacts of COVID-19, as well as at wider individual and societal effects of the disease and to follow up individuals reporting long-duration symptoms. 


Image credit | Getty

Related Articles

“Diabetes in COVID-19 patients may be transitory”

Many COVID-19 patients newly diagnosed with diabetes during hospital admission may in fact have a temporary form of the disease related to the acute stress of the viral infection, it is claimed.

New diagnoses have plummeted in the pandemic

New diagnoses of common chronic conditions have dramatically declined during the COVID-19 pandemic, according to a new study.

"Common cold T cells protect against Covid"

A new study led by Imperial College London researchers provides the first evidence that T cells from common colds could cross-protect against infection with SARS-CoV-2.

mRNA injection to make CAR T cells

An experimental immunotherapy can temporarily reprogramme patients’ immune cells to attack a specific target via a single injection of messenger RNA (mRNA), similar to the mRNA-based COVID-19 vaccines, according to a new study.