Publicação: 18 de janeiro de 2022
Vaccines keep human immunological systems primed and healthy
Researchers at Weill Cornell Medicine and the University of Oxford announced on January 10, 2022, their new study shows that common vaccines could help reduce the health burden of the COVID-19 pandemic.
A peer-reviewed study published in the Proceedings of the National Academy of Sciences crystallizes decades of evidence suggesting that the generalized immune-boosting properties of many vaccines can cross-protect people against multiple pathogens.
While these researchers did not specify particular vaccines, they chose values for cross-protection consistent with data from earlier studies on measles, influenza, tuberculosis, and other immunizations.
Their model found that an unrelated vaccine providing just 5% protection against serious COVID-19 would have produced a substantial reduction in caseloads and hospital usage.
“We know that unrelated vaccines have these heterologous effects, and a reasonable person could tell you that if you used them during a pandemic, it would benefit,” said Dr. Nathaniel Hupert, an associate professor of population health sciences at Weill Cornell Medicine and lead study author, wrote in a press release issued on January 10, 2022.
“This modeling study shows the potential power of all vaccines in keeping the immunological system primed and healthy, and reinforces the need for everyone to keep their vaccination history up to date, particularly during a pandemic.”
However, it wasn’t clear how much such an intervention would actually help.
Using the winter 2020-21 COVID-19 wave that struck the U.S., the investigators modeled the likely effects of a non-COVID-19 vaccine intervention at different times and targeting diverse populations.
The research team used the COVID-19 International Modeling Consortium (CoMo) system to address those questions, a sophisticated computer modeling platform they’d built in response to the pandemic.
“If you have a model that can be customized to a particular place and time in the context of an outbreak, you can start to experiment with different conditions of population immunity and see how things might have played out,” Dr. Hupert added.
“Surprisingly, we found a couple of really interesting emergent results from what we put in the mix,” Dr. Hupert said.
While COVID-19 severity correlates tightly with age, an experimental scenario that modeled vaccinating everyone over the age of 20 was more effective than strategies targeting only the elderly.
That could be because younger people tend to have more social contacts across age groups, making them more likely to spread the virus to more vulnerable populations.
The timing of the vaccinations also mattered, with delivery during the rising phase of the wave of infections having the most significant impact.
Some of the best-studied heterologous vaccine actions are from “off-target effects” from the Bacillus Calmette–Guérin (BCG) vaccine.
Epidemiological evidence, including several randomized controlled trials (RCTs), has assessed the effect of BCG vaccination on reducing neonatal mortality. For example, in Guinea-Bissau, two RCTs of BCG given to low weight neonates showed a reduction in neonatal mortality after BCG, mainly because of fewer cases of neonatal sepsis, respiratory infection, and fever.
A meta-analysis of three RCTs of BCG-Denmark showed a reduction in a mortality rate of 38% at 28 days of life; marked reductions in mortality were also seen within three days after vaccination and at 12 months of age.
Interestingly, a BCG vaccination before influenza vaccination can boost influenza-specific immunity.
Because of the nonspecific benefits of BCG vaccination, a phase III trial called “ACTIVATE-2” assessed whether BCG could protect against COVID-19 in the elderly; prepublication findings suggest a 68% risk reduction for total COVID-19 clinical and microbiological diagnoses.
A separate study showed that a history of BCG vaccination was associated with a decreased SARS-CoV-2 seroprevalence across a diverse cohort of healthcare workers and reduced COVID-19 symptoms.
The magnitude of protective effect against the symptomatic disease was similar in both studies: a reported range of 10 to 30% reduction in all respiratory infections in the former and a 34.5% reduction in the self-reported diagnosis of COVID-19 in the latter.
‘These results may be generalizable beyond COVID-19 and the US to indicate how even minimally effective heterologous immunization campaigns could reduce the burden of future viral pandemics,’ wrote these Weill Corneil Medicine researchers.
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