It has been more than two years since the covid-19 pandemic began, and since then, more than 6 million people around the world have died from the SARS-CoV-2 virus. The other side of the coin is that we currently have a wide range of treatments y vaccines highly effective drugs that have helped reduce the number of severe cases.
Even so, some people are more likely to become seriously ill or die from the SARS-CoV-2 virus than others. Our research on this topic, carried out before the start of vaccination against covid-19, showed that the obesity significantly increases the risk of hospitalization or death from this disease.
Obesity is classified by body mass index (BMI). It is a simple measure of body fat that is calculated by dividing weight in kilograms by height in meters squared. A person with a BMI of less than 18.5 is considered underweight; the range of 18.5 to 25 is classified as a healthy weight; above 25, overweight; and above 30, obesity.
These early results on the most vulnerable individuals were used to justify and support policies that prioritized vaccination of certain groups of people. This was the case with those who had a BMI greater than 40, who were considered high risk.
However, to date we did not know if this strategy had worked and if changes are needed to ensure that those most at risk can access vaccines in upcoming booster campaigns.
Some research done before the pandemic showed that people with obesity tend to be less vaccinated against seasonal flu. Furthermore, there is evidence to suggest that these vaccines they do not work as well in obese individuals, although the exact reasons are not fully understood.
In this sense, we wonder if the rates of vaccination against covid-19 and its effectiveness are different in people with different body weights. Therefore, we formulate a new study published in The Lancet Diabetes & Endocrinology to investigate this highly relevant question. We also studied the risk of severe disease after immunization across the body weight range.
To do this, we use the anonymous health records of more than 9 million people over the age of 18 in England. Our data spanned from December 8, 2020 (the date of the first vaccine administered in the UK) to November 17, 2021. During this time, 566,461 people with SARS-CoV-2 were registered, of which 32 808 were hospitalized and 14,389 died as a result of covid-19.
The efficacy of the vaccine is high, although it decreases slightly in people with low weight
To investigate the effectiveness of the vaccine, we compared people who were immunized with individuals of the same age, sex, and other characteristics who had not been immunized within the same BMI group. The results showed that the vaccines were highly effective against severe COVID-19 disease in all BMI categories, especially after the second and third doses.
For example, after the second shot, vaccinated people who were healthy weight, overweight or obese had almost 70% less chance of being hospitalized for COVID-19 compared to those who were not immunized with the same body weight.
Similarly, vaccinated individuals in the healthy weight, overweight, and obese groups were 60% to 74% less likely to die from this disease than unimmunized individuals with the same BMI.
The results, however, indicated that the effectiveness might be lower in underweight vaccinated people. They were about 50% less likely to be hospitalized and about 40% less likely to die than unvaccinated individuals in the same BMI range. Regardless, those efficacy estimates are still pretty good.
Additionally, underweight people were also the least likely to be immunized. The proportion of unvaccinated with low BMI was higher in all age groups, while the percentage of individuals fully vaccinated with the second or third dose was higher between the overweight and obese range.
–source, Author provided
Vaccinated with a healthy weight are better protected against severe covid
We also looked at the risk of severe COVID-19 disease only among people who had been vaccinated with at least one dose. Although immunization greatly reduced the number of severe cases, underweight and obese people still had a higher risk of hospitalization or death from COVID-19 than those vaccinated at a healthy weight. These associations are very similar to those found before vaccination.
After the third dose, these associations faded and were less conclusive. The reason is that very few cases were recorded (53 deaths and 381 hospital admissions), since not all people at the time of the study had been able to access that third dose.
Therefore, future research is needed to confirm whether these associations persist after booster doses. In addition, our research also did not allow us to explore differences between the different vaccines or between the variants of the virus. Finally, it is necessary to clarify the mechanisms by which body weight influences the immune response to vaccination.
–source, Author provided
Implications of the results
These findings provide new evidence that can help people make the right decision about whether or not to get vaccinated. They can also serve as information for current vaccination programs to establish different priority groups for future booster doses.
People who have two doses receive a high level of protection against severe illness from covid-19, regardless of their body weight. Given the slight reduction in the effectiveness of the vaccine in people with low weight, it is possible that it is necessary to influence this group to increase the vaccination rate in them.
Although a reduced number of severe cases of the disease were reported among vaccinated individuals, those in the underweight or obese groups had a significantly higher risk of severe COVID-19 compared to those of healthy weight.
It is necessary to continue promoting public health policies that help people maintain a healthy weight, which can bring numerous benefits. One of them could help reduce the added burden of covid-19 disease in the vaccinated population.
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