- [Narrator] Chinese COVID-19 vaccines are being used

in dozens of countries.

- China has donated vaccines everywhere

for those countries who need help.

- [Narrator] But these shots have some

of the lowest efficacy rates

among globally used coronavirus vaccines,

ranging between 50 to nearly 80%.

Compare this with shots from Pfizer-BioNTech, Moderna

and Russia's Sputnik V.

The head of China CDC in early April said the efficacy

of some vaccines was not high.

And this also included ones from his own country.

So China is looking to bolster the protection rate

and one way is to mix and match different types of vaccines.

And this idea isn't new.

- We really welcome studies

that would look at mix and match regimens.

- [Narrator] Spain is also interested in combining vaccines

while researchers in the UK

and Russia are already studying this.

So as China joins the ranks

of countries looking to mix and match,

here's how it can be a key

to overcoming multiple vaccination challenges at once.

Most Chinese vaccines and other shots currently in use

require two doses, creating an opportunity to mix and match.

Some immunologists believe this could have a number

of benefits like boosting the immune response.

- The theory is that if you train the immune system

to recognize a virus in a slightly different way each time,

then you might get a broader

and more durable immune response.

- [Narrator] And a more robust immune response

is important since China has confirmed cases

of new and more transmissible variants

that were first identified in the UK and South Africa.

Mixing and matching for this reason has gotten support

from at least one Chinese drug maker so far.

Some immunologists also say

that mixing and matching could ease the pressure

from the vaccine supply chain.

So for example,

in countries that are rolling out Chinese vaccines

along with other supplies,

using two different shots could give doctors more options

when patients come in for the second dose.

But one of the most important reasons

is when there are severe side effects

from one of the vaccines.

- If someone perhaps has a strange

or severe allergic reaction to the first shot that they get,

perhaps then you could avoid that

by giving them the second dose from a different vaccine.

- [Narrator] The idea became particularly important

after regulators started investigating

rare blood clotting disorders linked

to AstraZeneca's COVID vaccine.

As of late March, 79 people in the UK

have had severe blood clots

out of the 20 million administered doses

of AstraZeneca's vaccine.

In France and Germany,

health authorities are advising younger people

who have received a first dose of AstraZeneca

to get a second dose of a different vaccine.

The drug maker said it's working with health regulators

and starting the rare blood clotting events

and possible causes.

While these upsides could bring China and other countries

closer to getting their population vaccinated,

health authority say there's still a lot to learn

about possible side effects or how it may affect efficacy

of the vaccines, especially when it comes

to combining shots made with different technologies.

- The vaccine, such as Chinese vaccine

and the vaccines by AstraZeneca and Johnson & Johnson

are vaccines that use a virus as the vector

to get the genetic instructions into your body.

- [Narrator] Whereas Pfizer-BioNTech and Moderna vaccines

use a new gene-base technology involving messenger RNA,

where molecules carry genetic instructions.

- So we're not too sure what happens

when you mix these two technologies together.

- [Narrator] Chinese health authorities have said people

can receive different brands that use the same technology,

but don't recommend mixing vaccines

with different technology so far.

But now trials with the combination

of two homegrown vaccines with different technologies

are underway in China with more than a hundred volunteers.

The country is also working on its own mRNA vaccine

and looking closely at approving Pfizer-BioNTech shot,

according to people familiar with the matter.

This would pave the way for China to mix and match

its more conventional vaccines with mRNA shots.

Similar to how researchers in the UK are studying

the combination of AstraZeneca

with Pfizer-BioNTech or Moderna.

Those results are expected as early as may

- Immunologists, when you speak to them

about this sort of process, are pretty enthusiastic about it

and optimistic that it's going to work.

But that's maybe the one big drawback

is we want to make sure that it works,

we want to make sure that it isn't worse,

you don't get a worse immune response

than if you had two doses of the same vaccine.

(gentle music)