Is a third dose really needed?


TThe UK is enjoying real success with COVID-19 vaccine coverage. About 85% of adults (44.8 million people) have received a dose of vaccine and 63% (33 million people) both doses, with about 160,000 doses a day still in administration.

Two-dose vaccination helps prevent infection and, in those who are still infected, decreases the impact of the virus by reducing the severity of the disease, infection transmission, and death.

Still, he plans to give people a third shot have been revealed by the Joint Vaccination and Immunization Committee of the United Kingdom (JCVI). The two main arguments for supporting a third dose are that the effectiveness of the first two strokes decreases over time and that new vaccines need to be taken to deal with viral variants, such as the delta variant. But what does the evidence say?

Several studies have investigated the durability of immunity against COVID-19, and its results are encouraging. Researchers have focused on specialized white blood cells called lymphocytes. Lymphocytes enter two main varieties: B cells, which make antibodies, and T cells, which can help the B cells respond or directly kill the COVID-19 virus.

Antibodies play a key role in stopping viruses from entering the body’s cells, which is what the virus needs to do to replicate. You can easily measure a person’s antibody levels in a blood sample, but data on a typical person’s antibody levels after vaccination or COVID-19 infection have been variable.

Most people have good persistent levels of detectable antibodies at least seven months. However, some other people have fairly low levels of antibodies or their levels they fall quickly after infection or vaccination. This variability makes it difficult to know the usefulness of antibody data to measure lasting immunity to infection.

A clearer picture can emerge if other indicators of immunity are taken into account: our B and T cells. recent prepress (research that is still pending review by other scientists) suggests that observing both antibodies and T cells provides a clearer picture of whether immunity has persisted.

And in a reassuring way, functional responses of T cells against COVID-19 have been detected. six months after infection. In the same way, memory B cells – Long-lasting cells in the hand in case the immune system encounters COVID-19 in the future – have been detected in people even when their antibody levels have dropped so low that they cannot be detected (although this research is also pending review). This suggests that even after antibodies have diminished over time, these people have the means to produce new ones quickly if they are confronted with coronavirus again.

Older people (> 80 years) tend to have less effective immune responses when they are infected or vaccinated, which means their overall immunity may be lower and they may disappear more quickly. In any reinforcement campaign it is likely to be prioritized. However, so far the data on the elderly has been encouraging. Another recent prepress has shown that older people produce a strong immune response after vaccination.

All of these studies are very reassuring. Added to what we know immune responses to viruses more broadly, there is growing confidence that immunity to COVID-19 is lasting, although long-term studies will still be needed. However, right now there is no strong evidence that people’s immunity needs to be completed.

Can current vaccines handle variants?

There are now several variants of the coronavirus in circulation, to date, four (alpha, beta, gamma and delta). variants of concern (VOC). They are variants that spread more easily, cause worse diseases or are less well managed by vaccines.

Initial studies on the effectiveness of vaccines against the alpha variant – one of the first discoveries – they have been encouraging. And while early data on the gamma variant suggests it may be a bit capable of escaping immunity, a later prepress suggests that the vaccines still protect them.

However, there have also been concerns about the delta variant data from Public Health England (also still in prepress) suggests that vaccines offer solid protection against it. Even when vaccines offer reduced protection – as seen with the beta variant – month early research (again awaiting review) suggests that they still protect against the worst impacts of the disease.

Tests show that vaccination works: immunity is durable and protects us from the worst effects of COVID-19. So why does the UK plan to make third reinforcement shots when there is no clear evidence that they need it? A major concern should be that most people in the world remain unvaccinated. In many low-income countries, only 1% of the percentage eligible adults they have received a dose of vaccine.

Poor vaccine coverage allows the virus to thrive. When it infects and reproduces in many thousands of people, it causes the virus an opportunity to mutate, which can lead to the emergence of new variants. It is no coincidence that all VOCs arise from areas with high levels of viral transmission. There are also at least seven variants of interest which have also emerged from areas with high levels of viral transmission. These are viruses that can be VOCs and are therefore being monitored to see what threats they could pose.

To prevent more VOCs from appearing, we need to spread the virus urgently, not just in the UK, but everywhere. Evidence so far does not suggest that there is an urgent need to give people a third dose of COVID-19 vaccine in rich countries like the UK. It would be better to give these doses to countries with low coverage, rather than launching a booster program. Because until we have high vaccine coverage around the world, we can never really expect to escape this pandemic.

Sheena Cruickshank, Professor of Biomedical Sciences, University of Manchester

This article is republished from The conversation under a Creative Commons license. Read the original article.

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