As massive amounts of vaccines continue to arrive in the country, talk about booster shots became stronger, even the issue of “mix-and-match.” Are “booster” shots the same as “third shot?” Is it safe to use a different vaccine after being fully vaccinated with another? Who should be prioritized in getting extra shots?
Dr. Rolando Enrique “Eric” Domingo, Director-General of the Philippine Food and Drug Administration (FDA), reminded during the Stop Covid Deaths webinar of the University of the Philippines titled “Covid-19 Booster na, Mix-and-Match ba?” that all the eight vaccine brands now in the Philippines are still under Emergency Use Authorization (EUA) and are still undergoing clinical trials.
“There is no completely certified vaccine brand yet in the Philippines. In the world, Pfizer is completely certified but only in the US FDA, and they have not yet applied for full certification, or not yet approved, in other countries. But even if still under EUA, their benefits far outweigh the risks. We focused on two areas: safety and efficacy before we gave them EUA,” explained Dr. Domingo.
Amendments to EUA
Of the eight vaccine brands in the country, only two, Pfizer and Moderna, were given amendments to their EUA for use on children aged 12 to 17 years old. Pfizer is also expected to apply for an EUA within the month for use on children five to 11 years old, he said. Of the eight brands, six are under a two-dose regimen while Sputnik Light and Janssen are given as single dose.
Dr. Domingo noted that the hot topic these days are the booster shots, or additional shots. The Health Technology Assessment Council (HTAC) decided to separate them into two categories. For the “Additional” dose, he cited Sinovac (CoronaVac) as an example.
“An interim recommendation of the World Health Organization (WHO) is to give a third dose as part of the primary series. They said that in the elderly and the immunocompromised, after giving the second dose, they did not see an immune response that’s high enough compared to the younger people so there’s a need for a third dose to be given at least 28 days after receiving the first two doses to get optimum effect of the vaccine,” he pointed out.
Immune response
As for the booster shot, Dr. Domingo said the next dose for booster is at least six months after the first two doses. Even if the immune response after the first two was good, there may be a possibility of the waning of the immune response so there’s a need for a booster.
The Department of Health (DOH) is targeting to give booster shots during the last quarter of the year with the AI (healthcare workers) and A2 (elderly) as priority because they are the most likely to experience breakthrough infection. Then by early 2022, the target will be the A3 to A5 of the population.
“There’s no need to immediately give boosters, and also, the objective is to vaccinate first the unvaccinated, at least 50 percent of the population, before giving extra doses, and that extra doses need not be given to everybody. Only those who are high risk and frequently exposed to the virus,” he said.
Final recommendation
The experts’ group of the DOH also advised to wait for the final recommendation of the WHO-SAGE (Strategic Advisory Group of Experts on Immunization) on giving the third dose, which will come out this month, and to have the unvaccinated get their jabs first before giving out an extra dose. “We will not achieve herd immunity if only 35 percent are vaccinated and with boosters, while 65 percent of the population are still unvaccinated.”
On the issue of mix and match, Dr. Domingo said here in the Philippines, more studies are needed because there are several vaccine brands in use here, compared to the US where there are only three brands.
Right now, Pfizer, AstraZeneca, Sinovac and Sputnik were the ones that applied for variations in their EUA for the third booster of the same brand. However, the HTAC already asked the FDA to study the “heterologous” vaccines. This means AstraZeneca is the primary vaccine, and the booster is Pfizer; Sinovac, then either Pfizer or AstraZeneca as booster; Moderna, with Pfizer as booster. “All these are being studied by the country’s vaccine experts,” Dr. Domingo noted.
He explained that there are many possible permutations and combinations that is why they passed on the data to the vaccine experts, who asked for about two weeks to look at it.
Right now, the DOH is already preparing guidelines for the roll out. “Possibly by the end of the month or by December, the boosters can be given first to health-care workers who are exposed to Covid, the elderly and vulnerable individuals, and then to the other segments of the population.”