Text by Henrylito D. Tacio
Although COVID-19 vaccination for adults remains effective in preventing severe disease, recent data suggest vaccination is less effective at preventing infection or milder illness with symptoms over time.
Emerging evidence also shows that among healthcare and other frontline workers, vaccine effectiveness against COVID-19 infections is also decreasing over time. “This lower effectiveness is likely due to the combination of decreasing protection as time passes since getting vaccinated,” states the US Centers for Disease Control and Prevention (CDC).
In the United States, COVID-19 vaccine boosters and additional vaccine doses are now authorized by the US Food and Drug Administration (FDA). The CDC recommends them for certain people.
“A COVID booster shot is an additional dose of a vaccine given after the protection provided by the original shot(s) has begun to decrease over time,” explained Dr. Lisa Maragakis and Dr. Gabor Kelen, senior director of infection prevention and director of the Johns Hopkins Office of Critical Event Preparedness and Response.
“Typically, you would get a booster after the immunity from the initial dose(s) naturally starts to wane,” they added. “The booster is designed to help people maintain their level of immunity for longer.”
The Philippines is following suit. Starting last November 17, health workers fully vaccinated for COVID-19 have started to get their booster shots. This was after the FDA had issued an emergency use authorization for the booster doses.
“(The booster shots are) only for healthcare workers for now,” said Dr. Edsel Maurice Salvana in his social media account. He emphasized that it is “voluntary,” meaning it is given only to those who are interested in having it.
Dr. Salvana is the director of the Institute of Molecular Biology and Biotechnology at the National Institute of Health at the University of the Philippines Manila. He is a clinical associate professor and research coordinator at the section of infectious diseases of the Department of Medicine at the Philippine General Hospital.
“Whatever primary series you got, you are eligible for only one shot of one of these three vaccines only: Sinovac, Pfizer, and Moderna,” said Dr. Salvana. “Only those who are at least six months from their second dose are eligible. This may change depending on the final release since some studies have given boosters as early as three months.”
From a pure safety standpoint, homologous boosters are more predictable, according to Dr. Salvana.
In simpler terms, “if you got Sinovac, Pfizer or Moderna, you should go for a third dose of the same vaccine,” he pointed out. “There is data that mixing (heterologous vaccination) is more likely to cause reactions.”
Frontline workers who are involved with COVID-19 patients and were vaccinated with Sinovac, “there is marginal preliminary data (which showed) that a single shot of Pfizer booster has an added 10% clinical protection compared to a third dose of Sinovac,” Dr. Salvana claimed.
However, he said, the protection against severe disease is the same. “The efficacy data is only for 14 days from the booster dose so these may change,” he said.
“For non-frontline healthcare workers, the decision point is whether you think the marginal added clinical benefit (but equal protection from severe disease) is worth the added risk of severe reactions,” he said.
Bottom line, here are the recommendations of Dr. Salvana:
· Got two doses of Sinovac after six months, more frontline, no allergy/adverse drug reaction (ADR) history: Pfizer booster
· Got two doses of Sinovac, more frontline, after six months with allergy/ADR history: a third dose of Sinovac
· Got two doses of Sinovac after six months, not a more frontline, no allergy/ADR history: either Sinovac or Pfizer (personal choice)
· Got two doses of Sinovac after six months, not a more frontline, with allergy/ADR history: a third dose of dose Sinovac
· Got two doses of Pfizer or Moderna after six months ago, either frontline or non-frontline health care worker (HCW): use the third dose of the same brand (note, Moderna booster is half dose)
· Fully vaccinated HCW with any other vaccine, non-frontline or frontline (Janssen, Astra, Sputnik V, etc.): no clear preference on what booster to take (Pfizer, Moderna, Sinovac), might want to wait for more data. If with allergy/ADR, Sinovac might be safer.
“These recommendations are subject to change as the science trickles in, and are by no means final,” Dr. Salvana said. “If you have a hard time deciding, it might be safer to wait for more data.”
What will happen after you get your booster or additional dose?
“So far, reactions after getting a booster shot were similar to that of the 2-shot or single-dose initial series,” CDC says.
“Fever, headache, fatigue and pain at the injection site were the most commonly reported side effects, and overall, most side effects were mild to moderate. However, as with the 2-shot or single-dose initial series, serious side effects are rare, but may occur,” CDC says.