Covid -19: How often should we get the vaccine – What a new study shows – 2024-03-09 21:53:59

A computer model developed by researchers at the Stanford University School of Medicine reveals when older people, younger people and even the immunocompromised should get an updated vaccine to be protected.

Many patients kept asking the same question to infectious disease expert Nathan Law, an assistant professor at Stanford School of Medicine: “When should I get a booster shot for COVID-19?”

“It’s a question that everyone asks. My patients, my friends and relatives. And we experts refer them to the national vaccination recommendations, although this particular question is becoming increasingly difficult to answer as time goes by,” said Dr. Lo in a press release.

The new simulation model

Trying to find a scientifically documented answer, he and his colleagues resorted to computer models. They developed a simulation model based on COVID-19 surveillance and vaccination efficacy data collected by the US Centers for Disease Control and Prevention (CDC). The model as well as the findings resulting from its use are published in the scientific journal “Nature Communications”.

At least once a year for those over 65

So based on the results, people over 65 or those with weakened immune systems for different reasons need booster doses more often – at least once a year – to protect against hospitalization or death. For younger people, the benefit of frequent booster vaccination against severe disease is less.

For each of us but also for the authorities

The researchers hope that the model they developed will help both individuals know when they should get a booster dose of the COVID-19 vaccine and public health policy makers. “We’re now in the fourth year of the pandemic, and we’re turning to longer-term containment strategies,” said Stanford University data scientist Haley Park, lead author of the new study, adding, “We know that vaccination protection declines with over time and we also know that the risk of serious illness is very heterogeneous in the population. So it’s next to ask when is the right time for re-vaccination”.

Doing micro-simulation

The new model does so-called micro-simulation in which a large population is simulated but the results are valid at the individual level, Dr. Park explained. The research team used weekly CDC surveillance data from September 2022, when the bivalent booster vaccine first became available in the US, and their model predicted how many serious infections resulting in hospitalization or death would occur in different age groups over a two-year period. years. The calculations were based on different scenarios: receiving only one booster dose, receiving a booster dose once a year or a booster dose every six months.

Vaccine twice a year for those over 75

It found that for people over 75, getting a booster shot once a year reduced serious infections from about 1,400 per 100,000 people to about 1,200 per 100,000 people per year. But if people in this age group got a booster shot twice a year, serious infections dropped to about 1,000 per 100,000 people. The results were similar for people with moderately to severely weakened immune systems, while in people aged 65 to 74 the reduction in serious infections was about half.

The benefit of annual vaccination for the youngest is small

For younger healthy people, however, the reduction in serious infections was much smaller: annual booster vaccination or twice-yearly booster vaccination appeared to reduce serious infections in people aged 18 to 49 by just 14 to 26 cases per 100,000 people .

Lots of parameters

“In this particular study we focused on reducing serious infections that lead to hospitalisation. However, there are many other parameters that influence the decision to vaccinate,” noted Professor Lo.

Everyone benefits from ‘real’ updated vaccines

The researchers considered how new variants of the SARS-CoV-2 virus as well as its transmission affect the decision to receive a booster dose. They looked specifically at the effect of the new variants on escaping the immune system and found that the benefit of more frequent booster doses was greater for all age groups if the updated vaccines contained variants of the virus that were at the time possibly “related” to the most recent ones circulating in the population.

Reduction of mild infections in all age groups

In addition, the research team looked at the effect of booster vaccination on virus transmission and found that more frequent vaccination for all age groups led to less overall transmission, which had an additional benefit for “high-risk” groups.

The researchers also noted that frequent booster vaccination also appeared to reduce mild infections in all age groups.

“Shield” the previous illness

The scientists also included previous infection with COVID-19 in their model and saw that there was less benefit from frequent vaccination against severe disease in people who had previously been ill compared to those who had never been ill with SARS-CoV-2.

The variables that were not taken into account

However, there were variables that were not included in the study: for example, the probability of infection for each group was assumed to be the same over time, even though the risk of infection differs in real life. Also, people with immune system problems were divided into only two groups, although this population is much more heterogeneous, and the model also did not take into account hesitancy to get vaccinated or the risks of developing long COVID.

Update (and) the model

Dr. Lo and his colleagues (which also included researchers from the Yale School of Public Health, the University of California, San Francisco, and the California Department of Public Health) plan to update their model with new data as it becomes available with in the hope of shedding more light on the difficult question of booster vaccination. “In science there are some questions that become easier to answer as time goes by and some that become more difficult to answer as time goes on. The specific question belongs to the second category” concluded the professor.