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COVID-19: Why countries have different outcomes from similar vaccines

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Vaccination speed, dose intervals, demographics of the vaccination programme and natural immunity may be some of the factors behind the variations.

COVID-19: Why countries have different outcomes from similar vaccines
The effectiveness of vaccines against the COVID-19 pandemic has been well-researched. Vaccination reduces hospitalisation, cuts chances of severe symptoms and death and gives overall protection against the SARS-CoV-2 virus. It is also known that the Delta variant of the virus can cause breakthrough infections -- which is why restrictions and masks are still important. Further, there is a marked difference in the post-vaccination scene across different countries, which has kept researchers busy.
What’s the difference?
In countries like the UK, Denmark and Germany, COVID-19 deaths have fallen to below 10 percent of their previous peaks, according to data collected and reported by Bloomberg. But at the same time, nations like the US and Israel only saw a moderate decrease of less than 50 percent in death rates.
In countries that have relied on the Russian-made Sputnik V and an assortment of Chinese vaccines, death rates have seen only a moderate decline, precipitated mostly by the breakthrough Delta variant.
Why the difference?
The difference in the infection and death rates cannot only be put down to the different vaccines being used, rather a variety of factors are responsible. While some factors may have been identified, more research is needed for a better understanding of the disparate outcomes.
“There are a lot of factors beyond vaccinations that contribute to different outcomes across locations,” Natalie Dean, an assistant professor of biostatistics at Emory University, told Bloomberg.
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“Even in places with high vaccinations, we see Delta can cause a spike in cases. But do you see a strain on the health care system? And in the end, I think we are seeing more variability in that outcome as well,” she said.
The most likely factors, based on the data collected, are dose intervals, vaccination speed, age demographics, and levels of natural immunity, according to an analysis by Bloomberg, the news organisation reported.
What do these factors mean?
Research has shown that increasing the interval between two doses, at least for the AstraZeneca vaccine and the Pfizer-BioNTech vaccine, leads to a stronger immune response. In countries where the interval was approved to be on the longer side of the spectrum, cases and deaths may have been lower due to a stronger immune response from these vaccines.
“They (vaccinated individuals) may have had a much more superior response because we know immunologically that people’s immune systems may be much better primed for that second dose if they wait until that whole maturation process is accomplished,”  said Michael Osterholm, Director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
While the US and Israel were among some of the countries that were lauded for their quick vaccination uptakes, these countries also faced a higher number of cases than previously expected during the Delta spike. The counterintuitive reason behind the higher breakthrough infections is the quick vaccination pace in these countries.
With research now confirming that the Delta variant is able to break through more easily in people who were vaccinated much earlier, it is easy to see why these countries have also been quick to take up the mantle of booster doses for their population. The waning immune response causes more breakthrough infections, and immunity can be restored with booster doses.
Countries that focused on immunising their vulnerable population like the elderly, immunocompromised and those with co-morbidities found that they suffered fewer deaths. As more people who were susceptible to severe symptoms were protected, COVID-19 found fewer opportunities to cause deaths.
Natural immunity, the presence of antibodies in individuals due to exposure to the virus or previous infection, also plays a large yet mysterious role. Countries that managed to pass through the first wave of COVID-19 without much of a struggle are now cautious about the possible spread of the Delta variant, as the populace now lacks the additional protection of natural immunity.
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