Most anti-Covid vaccines are two-dose, and the usual vaccination strategy is for all people to get both doses of the same vaccine. But the Com-Cov study, led by Oxford University, recruited over 800 participants from the UK to investigate the effects of two different dosing vaccinations.
The study considered two vaccines: Pfizer and AstraZeneca. The combination of the two doses is not only safe but also protects more against Covid-19, reports abcnews.al
However, the exact benefits depend on which dose is taken first and which second. If people take the first dose of AstraZeneca and then Pfizer the level of antibodies against coronavirus spike protein will be higher compared to two doses of AstraZeneca or Pfizer vaccination.
The first dose of AstraZeneca and then the second dose of Pfizer resulted in a better T cell response than all other dose combinations. T cells – also known as T lymphocytes – are immune cells that help destroy foreign pathogens (such as the coronavirus) and produce antibodies.
The study will further examine whether the combination of doses provides better results if there is a gap between the two doses. The interval between doses in this initial trial was 28 days.
Several other researchers have also studied the combination of different types of vaccines to combat COVID-19. According to a Spanish study, people who first received the AstraZeneca vaccine had increased immunity when given a second dose of the Pfizer vaccine – providing more evidence that Pfizer works better as a booster, reports abcnews.al
To understand why these beneficial effects can occur, it is important to understand how the AstraZeneca and Pfizer vaccines work. Both vaccines have a key element of the coronavirus – spike protein – in the immune system.
Pfizer “accumulates” the genetic code for coronavirus spike protein in fatty nanoparticles. When these particles enter the cells of the body, the code is deciphered and copies of the spike protein are produced, leading to an immune response.
The AstraZeneca vaccine has the same genetic code but uses an attenuated form of a common virus (an adenovirus) from chimpanzees to transmit the code to cells. When you receive the first doses of the vaccine, there is a possibility that an immune response is produced not only against the S protein but also against the transporters used to send the signal, reports abcnews.al
If the second dose is the same, the developed immunity against the carrier will react against the second dose, eliminating some of it before strong, protective, and long-term immunity develops.
That is why Russia’s Sputnik V vaccine – which has the same method as the AstraZeneca vaccine – uses two different adenoviruses as carriers for its first and second doses, and has achieved impressive results.
Why is combination of doses so important?
There are additional benefits to combining vaccine doses in addition to protection. Logistical problems may arise when a second dose of vaccine should be identical to the first. Producing the same two doses takes time, so taking another dose can speed up vaccination of the population.
Second, if a person reacts badly after receiving the first dose they are more likely to take the second dose of another vaccine to provide better protection. Governments can also determine if a vaccine is not very suitable for certain groups of people, as has happened with AstraZeneca.
Supplying vaccines to some low- and middle-income countries can also be difficult, especially if they do not have the necessary storage requirements at the right temperatures.
Incorporating vaccines into the distribution plan that do not require storage at very low temperatures may make their distribution easier. But the combination of vaccines has many benefits. However, this study looked at only two types of vaccines – but over time, each combination must be tested, in every age group and in every ethnicity.
This study suggests that the combination of anti-Covid vaccines is beneficial and effective. /abcnews.al