Study confirms that combining booster vaccines provides greater protection against COVID-19

A study carried out in Chile has shown that, in general, the application of a booster dose of the vaccine against COVID-19 provides high protection against infection (spreading), hospitalization, ICU admission, and death, compared to those who only received two doses.

In addition, the research evaluated the effectiveness of the application of a third dose of Sinovac, AstraZeneca and Pfizer after a scheme of two applications of Sinovac’s inactivated virus vaccine, which uses the same technology as Sinopharm, used in Peru.

The combination of vaccines from different manufacturers and technologies is known as a heterologous scheme. In this case, the study compares the effectiveness of applying a homologous booster (the same vaccine: Sinovac) versus a heterologous one (AstraZeneca or Pfizer) in people who have received two doses of an inactivated virus vaccine.

“Our results suggest that a homologous or heterologous booster dose for people with a primary vaccination schedule with CoronaVac [Sinovac] provides a high level of protection against COVID-19, including illness and death,” the authors of the study published in the journal Lancet Global Health.

The results show that the Sinovac reinforcement has an effectiveness of 65.6%; Pfizer’s, 93%; and that of AstraZeneca, 88.9% compared to the two-dose scheme. The heterologous scheme was more than 90% effective in preventing death and between 82 and 95% against hospitalization and admission to the ICU.

The researchers point out that “heterologous boosters showed greater vaccine effectiveness than a homologous booster”which supports the decision of several countries de apply a third dose of a different brand.

“The first thing to note about this study is that it analyzes a vaccine similar to Sinopharm, which is Sinovac. In addition, the important thing is that it is proven that having a booster dose increases protection against death by more than 90% than those who have only two doses, and that the use of a different vaccine for the booster is more effective than applying the three equal doses”explains the medical researcher Percy Mayta-Tristán, director of research at the Universidad Científica del Sur.

“This study confirms the importance of advancing with the booster dose (third dose) in the population to increase protection against serious illness and death”, adds the expert.

In Peru, the health authorities administer a heterologous scheme for reinforcements in those people who received Sinopharm. The vaccines used for this purpose are AstraZeneca, Pfizer and Moderna.

The study analyzed data from more than four million Chileans who received the first two doses of Sinovac and then a booster from AstraZeneca, Pfizer (heterologous), and Sinovac (homologous).

The authors also recommend that the immunization schedule against covid with inactivated virus vaccines such as Sinovac and Sinopharm must be three doses and not just two, which is the original formulation.

The period covered by the study does not include the time when the Omicron variant of SARS-CoV-2 became dominant in the world.