The Science Behind Covid-19 Vaccine Recalls: Do We Really Need An Extra Injection ?, World News & Top Stories


It is only at the beginning of the year that “Have you been vaccinated?” has become the standard greeting in many countries. Now this should be repeated as: “Do you have your booster shot?”

Some countries, including Singapore, Israel, Germany and France, have started giving an extra dose of a Covid-19 vaccine to the elderly and the immunocompromised as studies show decreased immunity to the coronavirus in the over time after the first injections.

The move sparked a debate over whether the boosters are really necessary and whether it is ethical and fair.

The discussion took a new turn this week as new data corroborated earlier findings – which had yet to be peer reviewed – that the efficacy of Pfizer and Moderna’s vaccines declines within months, and that ‘An extra dose of Pfizer vaccine can reduce infection rates by 11 times and serious illness by 20 times in the elderly.

There are many arguments for and against boosters, but what primarily concerns policymakers and healthcare professionals is whether science shows them to be a necessity.

In considering this, we look at three key questions: Are immunity levels really going down? Will additional injections really help and are they safe? What are the broader implications of giving another injection to those already vaccinated?

Immunity: antibody levels and real world data

Scientists generally view antibody levels as an indicator of vaccine effectiveness. Early studies have shown that the levels of antibodies generated by Covid-19 vaccines decrease over time. But this is perfectly normal.

“There is no vaccine where you don’t see a drop in antibody titers over time,” Professor Rafi Ahmed told the science journal Nature, referring to the unit of measurement for antibodies.

“There is always a drop,” said the immunologist and director of the Emory Vaccine Center in the United States.

It’s not so much about the quantity of these antibodies, but rather their quality – whether they effectively protect the body from the ravages of the invading virus. But how to measure this with certainty is less clear, say the scientists.

“If you had high levels of antibodies against every pathogen you come across, your blood would be mud,” said Dr. Jane O’Halloran, assistant professor of medicine at Washington University School of Medicine in St. Louis. “Sometimes the easy to measure bit isn’t the thing that gives us the best window into what’s going on in the body.”

With science still unclear as to whether antibody levels are directly proportional to protection against infection and the severity of disease, experts have turned to examining real-world data.

A new study published by Moderna this week showed higher infection rates in U.S. volunteers vaccinated with its vaccines about 13 months ago compared to those vaccinated about eight months ago.

The vaccine maker also reported a downward trend in the rate of severe cases among those most recently vaccinated, but said the result was not statistically significant.

Recent studies in Israel have also shown that people vaccinated with Pfizer injections earlier in the country’s vaccination schedule were significantly more likely to catch Covid-19 and even to suffer from severe illness from the virus over time. month.

Some experts point to other factors at play, such as the arrival of the more transmissible Delta variant and the fact that many of those people vaccinated earlier were either healthcare workers who tended to be more exposed to the virus, or people who are immunocompromised.

But others also note that the number of severe cases in Israel, which had increased after the arrival of the Delta strain, stabilized weeks after the rollout of the booster shots began in mid-August. New weekly hospitalizations have now fallen to around 1,200, from a peak of over 1,400 in late August.

Risks: Side effects and immune depletion

There is little evidence that booster injections elicit stronger immune responses. But with the initial doses already preventing most people from going to the hospital, the benefits of an additional injection may be marginal for a large majority of people.

In Israel, nearly six in ten Covid-19 hospital patients had been fully vaccinated, reports showed last month. This is in part due to the country’s high vaccination rate, at 62 percent of its total population. But the data also revealed that nearly 90% of those hospitalized were over 60 and had chronic illnesses.

Experts note that some immunocompromised people are simply unable to produce sufficiently high levels of antibodies, even after a full vaccination. Even with a third dose, their antibody levels – although improved – tend to remain lower than those seen in other vaccine groups, according to a study of organ transplant patients on immunosuppressants published last month in the New England Journal of Medicine.

These results can scientifically justify the offer of additional vaccines to the elderly and those with co-morbidities, however marginal the protection may be. However, the jury is still out on whether healthy adults should get them as well.

So far, trials suggest that the side effects of an extra jab won’t be too different, said Professor Ahmed of the Emory Vaccine Center. For most people, the side effects were mild, but a small proportion suffered from more serious problems, such as blood clots and inflammation of the heart.

Each additional injection also carries a risk of immune depletion, which means the immune system learns to tolerate the virus rather than recognizing it as a threat and working to destroy it.

“There is obviously a risk in continually trying to increase an immune response,” Dr. Marion Pepper, immunologist and associate professor at the University of Washington, told The New York Times. “If we go into this boost cycle every six months, it’s possible that it works against us. “

Wider implications

Essentially, when deciding whether or not to offer booster injections, decision-makers should keep in mind their ultimate goal: is it to prevent serious illness and death, reduce transmissions, or stop them altogether. infections?

All three would be ideal, but which one is the most critical?

Vaccines have never promised to eradicate infections – vaccinees can still catch Covid-19 – so stopping them altogether would be a pipe dream in modern society with its porous borders and geographically mobile people.

There is some hope in reducing transmissions, however, as research to date has shown that vaccinated people may be less likely to be infected, and if they catch the virus they can produce lower viral loads and therefore be less contagious to others.

While booster injections, by boosting the immune response, can help further reduce the chances – however small – that a fully vaccinated person will become infected or become more infectious, it may also better protect members of the public, especially those who are , for medical reasons can not be vaccinated.

“(A reminder) will ultimately prevent others from going to the hospital, and that will ultimately benefit the way the country is going,” said Professor Michel Nussenzweig, immunologist and senior physician at Rockefeller University in the United States. .

U.S. Food and Drug Administration advisers have recommended Pfizer boosters for people aged 65 and over and those at high risk of serious illness, although they rejected granting more approval. large, citing a lack of evidence in the American context.

If stronger data emerges or the pandemic worsens, everyone may eventually need boosters. But until then, it seems to be good for some but not necessarily for others.

Critics of the recall deployments view countries offering extra doses at the expense of millions of others around the world who are sorely lacking in doses at all as selfish and unfair. After all, no one can need a third dose more than someone who needs the first.

But if you consider only the science of the matter, it’s no wonder that policymakers are inclined to offer booster shots to some.

As Dr Dvir Aran, assistant professor of biomedical data science at the Technion-Israel Institute for Technology, said: “The risk is low, the benefit is high.

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