Study says delay in 2nd dose can reduce death rate – under two conditions

MANILA, Philippines — A predictive modeling study has found that delaying the administration of the second dose of a COVID-19 vaccine among those age 65 and lower could lead to an overall lower mortality rate in a population, but only if certain conditions are met.

The US study, which was published in the British Medical Journal, said the conditions must be that the vaccine should have a one-dose efficacy of at least 80 percent, and that the population in question should have a daily immunization rate of between 0.1 percent and 0.3 percent of the total population. If these conditions are met, researchers said mortality rate can be reduced by up to 20 percent.

“The results suggest that under [these] specific conditions, a decrease in cumulative mortality, infections and hospital admissions can be achieved when the second vaccine dose is delayed,” wrote the researchers led by the Thomas Kingsley of the Mayo Clinic in Rochester, Minnesota.

83K daily in PH

On Thursday, the National Task Force chief implementer and vaccine czar Carlito Galvez said the country was inoculating about 83,000 individuals daily. With the Philippine population estimated at 110.59 million in 2021, this would place the average rate of daily immunization at 0.07 percent, or less than the required 0.1 to 0.3 percent mentioned in the US study.

Galvez said the daily inoculation “will increase over the [next] days, considering that we are increasing our capacity and we are activating vaccination sites.”

As of Tuesday, data from the Department of Health showed that 2,025,038 people in the country have gotten their first dose. This represents 78 percent of all available first doses of the vaccine.

Meanwhile, 514,655 people have gotten their second dose, which accounts for 20 percent of the country’s allocation of second dose vaccines.

The delayed delivery of the vaccines has slowed down the country’s vaccination drive and has led to earlier fears that the second dose, particularly for those who received AstraZeneca vaccines as their first dose, would not arrive on time. (See related story on this page)

At a briefing in early April, Health Undersecretary Maria Rosario Vergeire said the delay in the shipment of additional AstraZeneca vaccines would not affect the administration of the second dose which, she said, can be given up to 12 weeks after the first jab.

‘Mix and match’

A separate Oxford University-led study meanwhile reported its first findings on the symptoms experienced by those who received vaccine shots from different manufacturers for their two doses. The most common postvaccination symptoms are a sore arm, chills, and fatigue.

The Oxford study found that people vaccinated with a shot of Pfizer’s vaccine followed by a dose of AstraZeneca’s, or vice versa, were more likely to report mild or moderate symptoms, such as headaches or chills, than if they received two doses of the same type of vaccine.

Pfizer and AstraZeneca were the first vaccines available in Britain to undergo trial in the “mix-and-match” study. Shots by Novavax and Moderna have since been added to the research.

Key data on immune responses generated by the different combinations of mixed or regular dose schedules are expected to be reported in the coming months, according to Matthew Snape, the Oxford University professor leading the trial. —With a report from Reuters