EXPLAINER: Why do COVID-19 vaccines require 2 doses with different intervals?

By NG Seruela

The Philippines’ available COVID-19 vaccines for inoculation require two doses to reach full efficacy.

According to the Department of Health (DOH), the following are the vaccines’ intervals between the first dose and the second dose:

  1. Sinovac: 2 doses, 4 weeks (28 days) apart
  2. AstraZeneca: 2 doses, 4 to 12 weeks apart
  3. Gamaleya Sputnik V:  2 doses, 3 weeks apart
  4. Pfizer: 2 doses, 3 weeks apart

National Task Force against COVID-19 (NTF) Medical Adviser Dr. Ted Herbosa explained in a Laging Handa public briefing that the first dose will trigger the immune response of the body. He said that in the first jab, the body will produce antibodies against COVID-19.

“Ang unang dose ay magti-trigger ng tinatawag na immune response sa ating katawan. So…iyong Sinovac at iyong AstraZeneca, both of them mayroong tinatawag na antigens, iyong foreign body na nagku-cause ng aming immune response na mag-produce ng antibody,” he said.

He emphasized that the second dose is called the ‘booster dose’ because it intends to boost the immune system, therefore producing more antibodies. He added that the second dose also provides a longer protection from the virus.

According to an article (How do vaccines work? (who.int)) of the World Health Organization (WHO), vaccines have different intervals because the intervals are needed to “allow for the production of long-lived antibodies and development of memory cells.”

“In this way, the body is trained to fight the specific disease-causing organism, building up memory of the pathogen so as to rapidly fight it if and when exposed in the future,” it added.

Moreover, DOH-Technical Advisory Group (TAG) fellow Dr. Ed Salvana explained that “catch-up vaccination,” where the recipients receive their second dose at a later date than the recommended schedule, is not a big deal. However, he urged the public to follow the set schedule for their second dose.

“Ginagawa naman po talaga iyon in practice. Mas maganda pa ring sundin natin ang [recommended schedule] pero kung mahuli ng kaunti ay hindi naman malaking bagay iyon… E-epekto pa rin naman ang ating bakuna, bagamat mas maganda pa rin to get the second dose on time para ang full protection natin ay makuha na as soon as possible,” he said. -jlo

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