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Saturday, November 26, 2022

Do you need a fourth dose of the COVID vaccine? an epidemiologist has evidence

In late March 2022, the US Food and Drug Administration authorized a second booster shot of COVID-19 vaccines for vulnerable populations in the US, a move that followed soon after endorsed by the Centers for Disease Control and Prevention.

People 50 years of age and older and certain immunocompromised individuals who are at high risk for serious illness, hospitalization, and death are eligible for four months after receiving the initial booster shot.

A second booster shot is equivalent to a fourth dose for people who have received Pfizer-BioNtech or Moderna mRNA series, or a third dose for people who have received the single-shot Johnson & Johnson vaccine.

In Israel, people from these same vulnerable groups began receiving the fourth dose in January 2022. The UK recently began giving a fourth dose for people aged 75 and over and called it a “spring booster”. In Germany, people over the age of 60 are now eligible for a fourth shot of the mRNA chain.

I am an epidemiologist at the University of Texas Health Science Center School of Public Health and the founder and author of Your Local Epidemiologist, a newsletter translating the latest public health science for daily use.

The latest recommendations have left many wondering about the importance of boosters for protection against COVID-19. Does the third shot wear out over time? Is a fourth dose necessary? What if you already have an infection?

After reviewing a growing body of research on how the immune system changes over time after each dose, it is clear that for vulnerable populations another booster has a meaningful benefit with very little risk.

Vaccine effectiveness after first booster dose

There is clear evidence that the third dose of the mRNA chain – or the first booster dose – was and is still important to ensure a strong immune response against the Omicron type for all age groups. This is partly because the immune response tends to diminish over time and partly because Omicron has been shown to be effective partly in developing immunity from existing COVID-19 vaccines and prior infections.

But then the question becomes: How good is immunity from the first booster over time?

The best real-time data to follow on vaccine effectiveness over time is in the UK. The UK Health Protection Agency currently has follow-up data for 15 weeks after the third dose or the first booster shot.

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In its latest report, the effectiveness of vaccines against infection drops significantly after the third dose. In the UK report, the effectiveness of the vaccine against hospitalization is much better than the effectiveness against infection.

But with the passage of time, the safety of hospitalization is also decreasing a bit. While this data is practical, the 15-week follow-up data is not very helpful in the US because many Americans got their third dose by 24 weeks ago.

A recent study assessed the durability of a third dose of Moderna after six months. The researchers found the level of neutralizing antibodies to be low six months after the booster. The CDC also found significantly weaker protection against emergency department and urgent care visits five months after the first booster.

The vaccine’s effectiveness against hospitalization decreased slightly, but remained substantially five months after the booster.

The studies described above pooled all age groups. But researchers do know that older adults do not have as durable immune responses as younger people. This explains why breakthrough infections have occurred at a much higher rate in people 65 years of age and older.

a recent study in Knife assessed the durability of the third dose in people aged 76 to 96 years. The researchers found that the third dose improved neutralizing antibodies, but in the face of Omicron, the antibodies still decreased significantly after the booster.

Data on second booster dose/fourth shot

Now that Israel has been delivering a fourth dose for several months, researchers have few data to rely on to assess its effectiveness. So far three studies have been released, one of which has not yet been reviewed.

In a study published in New England Journal of MedicineThe scientists assessed rates of infection and serious illness after the fourth dose — or second booster — among more than one million people aged 60 and older in Israel.

The researchers found that after the fourth dose, the rate of COVID-19 infection was two times lower than after the third dose. However, this protection quickly lapsed after six weeks. They also found that the rate of serious illness was four times lower than for those who received only three doses. However, it is important to note that the number of hospitalizations was very small between the two groups.

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Importantly, another study assessed the effectiveness of a fourth dose among young health care workers in Israel. The results confirmed that the antibody levels decreased significantly five months after the third dose.

Unfortunately, the effectiveness of the fourth dose was indistinguishable from the effectiveness of the third dose in this population of young health care workers. In other words, there may not be a meaningful benefit of another booster of the same formula for a younger, healthier population.

Researchers conducted a third study, which has not yet been reviewed, among people aged 60 to 100 in a larger health care system in Israel.

Of the 563,465 patients in the health care system, 58 percent received a second booster. During the study period, 92 people who received the second booster died, compared to 232 people who only had the first booster. In other words, the second booster equates to a 78 percent reduction in deaths compared to the first booster alone.

What if you got a COVID-19 infection from Omicron?

The combination of being vaccinated and experiencing a COVID-19 infection is called “hybrid immunity.”

Over 35 studies have shown that hybrid immunity provides complimentary and comprehensive protection. This is because immunity from vaccines targets the spike protein – after which COVID-19 vaccines were designed – and infection-induced immunity targets the virus as a whole more broadly.

Therefore, it is not unreasonable to leave a second booster with a confirmed infection of Omicron. This does not mean that people should purposefully acquire SARS-CoV-2, the virus that causes COVID-19. But it is clear that hybrid immunity is a viable route to protection.

In short, there is strong evidence that the fourth dose – or second booster – provides meaningful protection among vulnerable populations, including those over 60. So another booster is appropriate for some groups.

And while the fourth dose may benefit a select group, it is far more important that people receive their first, second, and third doses.Conversation

Caitlin Zetlina, assistant professor of epidemiology, University of Texas Health Sciences Center at Houston.

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