A medical assistant prepares a dose of a COVID-19 vaccine to be given to a patient. Photo credit: Public Domain image courtesy of Lisa Ferdinando, Department of Defense
Delaying the second dose of COVID-19 vaccines, at least for those under 65, could result in up to 20% lower mortality, but only under certain conditions, according to a US study published today by the BMJ.
These conditions include a one-time vaccine efficacy (effectiveness) of 80% or greater and vaccination rates of 0.1% to 0.3% of the population per day. If these conditions are true, the researchers could say the strategy could prevent between 47 and 26 deaths per 100,000 people.
Both the Pfizer and Moderna COVID-19 vaccines in a standard two-dose regimen are highly effective in preventing symptomatic infections and death. However, global immunity remains low, partly due to low vaccination rates.
The longer it takes to effectively vaccinate the world’s population, the greater the likely risk that vaccine-resistant strains will develop. This has led to the need to prioritize vaccination with a single dose for as many people as possible, even if this means that a second dose is delayed beyond the period studied.
The justification for this is based on the assumption that reasonable protection against COVID-19 can be achieved after a single dose of vaccine, which is, however, the subject of intense debate.
To investigate this further, a team of US researchers set out to measure the effects of delayed vaccine guidelines for the second dose on infections, hospital admissions, and deaths compared to the current scheduled two-dose regimen.
Using a simulation model based on a “real world” sample population of 100,000 US adults, they ran a series of scenarios to predict potentially infectious interactions under various conditions over a six-month period.
These included different rates of effectiveness and administration of the vaccine, as well as different assumptions about whether the vaccine prevents transmission and prevents serious symptoms or only prevents serious symptoms, including death.
They also looked at the effects of delaying the second dose for those under 65 years of age, but not before the elderly were fully vaccinated.
The results suggest that, under certain conditions, a reduction in cumulative mortality, infections, and hospital admissions can be achieved if the second vaccine dose is delayed.
The study repeated the simulations several times and used this data to estimate different outcomes at the population level. For example, for a first dose efficacy of 80% and a daily vaccine delivery rate of 0.1%, 0.3%, and 1% of the population, the estimated all-cause mortality per 100,000 for delayed versus standard second dose administration was 402 versus 442, 204 versus 241 or 86 compared to 50.
These results suggest that a delayed second dose strategy is optimal for vaccination rates at or below 0.3% of the population per day when the vaccine effectiveness is 80% or greater at one dose.
In addition, the delayed second dose strategy for those under 65 years of age performed consistently well at all vaccination rates tested, resulting in an absolute cumulative mortality reduction of up to an estimated 48 per 100,000.
These two conditions seem reasonable based on the US Centers for Disease Control and Prevention (CDC) estimate that the vaccine effectiveness is 80% in the first dose, and only some countries like the US and United States Kingdom achieved a vaccination rate of close to 1% the researchers.
They acknowledge some limitations of the study based on the assumptions used in the model, but aimed to capture the relevant complex human interaction that is critical to COVID-19 transmission over a period of time that is essential for Decision maker is useful. As such, they say these findings could be largely informative for the COVID-19 vaccine strategy.
“Policymakers need to consider their local vaccination rates and weigh the benefits of increasing those rates by delaying a second dose versus the risks associated with remaining uncertainty in this strategy,” they write. “These decisions should continue to be re-evaluated as new data become available,” they add.
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DOI: 10.1136 / bmj.n1087 Effects of delaying the second dose of the vaccine BNT162b2 or mRNA-1273 COVID-19 on public health: modeling study based on a simulation tool, www.bmj.com/content/373/bmj.n1087 Provided by British Medical Journal
Quote: Delaying the second dose of COVID vaccine may, under certain conditions (2021, May 12), prevent deaths from occurring on May 13, 2021 at https://medicalxpress.com/news/2021-05-covid-vaccine-dose-deaths -conditions.html were retrieved
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