Covid-19: why transmission among those who have 3 doses should not alarm – Health

When the omicron variant first emerged in South Africa in November 2021, there was great alarm at the exponential spread of the infection. That phenomenal speed of propagation surpasses what we have observed in previous variants.

The trend has been replicated in other parts of the world, including the UK where the number of infections doubled every other day in early December. What increased concern was that this rapid spread was occurring among a highly vaccinated (and hence, in theory, highly immune) population. Could the protection that the vaccine gave us be failing?

At first glance, it appeared that the vaccines weren’t working. But that depends on how the protection of a vaccine is defined. First, does the vaccine protect against infection?

There is currently ample evidence showing that vaccines are not very effective in preventing vaccinated people from getting infected or from spreading the infection.

That was graphically illustrated by the super-spreading event that took place in the Faroe Islands where 21 out of 33 health workers who were triple vaccinated and attended a private meeting got omicron. Furthermore, it happened despite the fact that several had had a PCR or antigen test 36 hours before the event.

Some – especially the anti-vaccines – might take this as proof that vaccines don’t work. However, that is not unexpected. Even against other variants, such as delta, it is known that vaccines do not offer “sterilizing immunity”, that is, a total prevention of infection.

No one has claimed that covid vaccines offer sterilizing immunity and that it may be an achievable goal. At best, they offer weak protection against infection. However, this weak protection could help slow the spread of the infection.

The role of the third dose

What vaccines do do is provide excellent protection of another kind. So far, vaccines have been shown to be very good at preventing severe disease. This protection is just as important, if not more so, because it keeps most infected people away from hospitals and death.

Against the delta variant, the protection of the vaccines against severe illness and death from covid was more than 90% with relatively little decay of protection over at least five months after two doses.

When omicron was first discovered, there were concerns that the mutations it would produce could allow it to bypass the protection of vaccines. Indeed, the data suggest that two doses of the Pfizer or AstraZeneca vaccines offered limited protection against omicron.

Fortunately, this protection of the vaccine was quickly restored by the booster dose, and therefore there is an urgency to “boost” the population.

This is especially important for those who are most vulnerable, such as the elderly, who, compared to the general population, are at higher risk of contracting severe COVID to begin with. A person 80 years of age has a 300 times higher risk of contracting severe covid compared to an adult under 40 years of age.

It is also vital not to forget that while omicron may be less severe for the vaccinated, it is still a dangerous infection for the unvaccinated.

The fact that sterilizing immunity against COVID does not currently exist probably casts doubt on whether “herd immunity” will end the pandemic.

What is believed here is that if enough people acquire immunity and this immunity blocks transmission, the virus will die off as there will be fewer and fewer people to infect.

Health systems under pressure

However, as omicron has shown, reinfections can occur even among highly vaccinated populations such as those in the UK and Israel. Omicron is reported to have a higher reinfection rate than other variants, and five times higher compared to delta.

Although omicron infections appear to be less severe, their increased risk of contagion means that more people are becoming infected. What’s more, the UK is registering its highest levels of infection in the last two years.

While these are not translating into higher levels of admission to intensive care units, the large number of patients with less severe illness can still put a lot of pressure on already depleted health services.

On top of that, the higher levels of illness among staff and more who have to isolate themselves due to infection add further pressure to the healthcare system.

This problem is not limited only to health care but to the width and length of society in general where high infection rates can cause significant alterations.

So vaccines are not the only solution. Other protective measures, such as face masks, more testing, and better ventilation, play an important role.

The weeks ahead portend to be challenging as people return to work and schools after the holidays, which could lead to more infections.

Better than a year ago

But the whole picture is not gloomy, and the current situation is certainly better than a year ago. In many high-income countries with extensive immunization coverage, the pandemic is gradually transitioning to endemic status.

At that time, the virus will still be present, but the disease will be more predictable. There will be high levels of the population with immunity either due to vaccination or natural infection that will mean fewer hospitalizations and deaths related to covid.

Annual immunizations against covid, particularly of the most vulnerable, will be required to maintain immunity protection for them. But we haven’t gotten to that yet.

Viruses mutate all the time, and other variants of covid will likely emerge in the future that can evade immunity and cause reinfections, as is the case with common human coronaviruses and influenza flu.

Although omicron luckily seems to be less severe, the risk remains of the emergence of more variants that may include a more severe one. Vaccines are still the best option against these.

* Andrew Lee is Professor of Public Health at the University of Sheffield, UK. His original article was published in The Conversation whose English version you can read here

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BBC-NEWS-SRC: https://www.bbc.com/mundo/noticias-59901838, IMPORTING DATE: 2022-01-07 11:20:05

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