Over the past few days, we have had quite a lot of discussion about Sinovac, one of the vaccines in the national vaccine inventory that is now being used in Malaysia. A lot of questions have been running on social media on whether the vaccine works or not, which has of course driven many to try to ‘choose their vaccine’. This instalment provides more information on ‘old-school’ vaccines- of which Sinovac is just one of many being developed to fight Covid-19.

While most of us are familiar with Sinovac since it is already being used in Malaysia, there are a few other vaccines made with ‘old-school’ technology; and some of them such as Sinopharm (developed and manufactured in China) and Covaxin (developed and manufactured in India) may soon make their way to our shores as well.

In previous instalments, we have covered quite a bit on how the ‘sexy’ vaccines using viral vector or mRNA technology worked. However, we shared little about vaccines from the ‘old-school’ of vaccine technology, thinking that everyone is quite used to these types of vaccines. Truth be told, with the exception of anti-vaxxers, the rest of us have all been receiving ‘old-school’ vaccines from the time we were born- think Hepatitis B, measles, mumps and rubella.

Why do we call these vaccines ‘old-school’ vaccines? Well the monicker ‘old-school’ or traditional vaccines refers to the fact that we use the microorganism causing the disease itself (whether in its whole form or in parts). This means that an ‘old-school’ Covid-19 vaccine consists of either a whole Covid-19 virus or part of a Covid-19 virus. Of course, we do not inject a healthy live virus as the vaccine. Rather, the virus being injected is either killed, or weakened in a way that it cannot cause an active infection.
Interestingly, ‘Old-school’ vaccines actually consist of a broad group of different types. The table below helps describe the 4 main groups of ‘old-school’ vaccines:

Now, let’s look at all three of the ‘old-school’ vaccines we were talking about. All three of the vaccines i.e. Sinovac, Sinopharm and Covaxin are inactivated vaccines. A virus is inactivated using heat, radiation of chemicals to destroy its genetic material, making it inactive. In the Covid-19 context, these three vaccines consist of a killed version of the Covid-19 virus.

When it is injected into your body, this dead virus will trigger your body’s immune system to produce an immune response against the Covid-19 virus by mobilising killer T cells (which identify and kill infected body cells), helper T cells (which support the production of antibodies) and B cells which produce antibodies.

Inactivated Covid-19 vaccines: How effective are they?

Inactivated Covid-19 vaccines, either because they are from China and India, seem to not have as good a reputation for effectiveness as their Western counterparts. However this is really not an accurate perspective.

Sinovac, for example, was widely tested in many different countries and yielded an average efficacy of between 51-84% in terms of mild or moderate disease. Sinopharm also had multi-country trials and reported an efficacy of around 78% while Covaxin had an efficacy of about 78% as well (though these are interim results of the trials at present). A lot of us are bothered about these numbers, as we like to compare them to the 95% efficacy of the Pfizer-BioNTech vaccine in terms of mild or moderate disease, but this is, again, a non accurate measure.

This is because when you look at efficacy in terms of severe Covid-19 disease such as hospitalisation or death; all three of these vaccines report the same efficacy as both the Pfizer-BioNTech mRNA vaccine or even the viral vector Oxford-AstraZeneca vaccine which is 100%!

So, an important mental correction many people need to make in terms of judging the efficacy of these ‘old-school’ vaccines is to understand that they are equally efficacious at preventing severe Covid-19 disease or death at the same levels as the ‘new-school’ mRNA vaccine or the viral vector Oxford-AstraZeneca one. This really should be the scientific data you need to take into account when deciding whether a vaccine is effective or not- and the data is quite clear- all the vaccines are equally effective.

Inactivated Covid-19 vaccines: Pros and Cons

One of the largest pros for inactivated Covid-19 vaccines are that they are based on tried and tested technology and have been used previously in many vaccines- most of which most of us would have taken. Inactivated virus vaccines are also much cheaper to make and have no live components in it, so there is little risk of the vaccine triggering the disease. Also, since the injected virus is not alive, it is more suitable for people with compromised immune systems.

However, inactivated Covid-19 vaccines are more difficult to make, and production of these vaccines initially involve growing the virus itself- quite a dangerous procedure needing highly secure facilities and stringent manufacturing processes. The other main con of inactivated vaccines is since they are made up of dead microorganisms, they cannot infect cells and thus can only stimulate antibody-mediated responses. This type of immune response may be weaker and not last as long, requiring booster doses over time. However, to overcome this problem, inactivated vaccines are often given together with an adjuvant (an agent that stimulates the immune system). All three of the inactivated vaccines Sinovac, Sinopharm and Covaxin use an aluminium adjuvant.

Inactivated vaccines versus the rest of the field: What is the difference?

The largest difference between inactivated vaccines and the mRNA or viral vector type of vaccine is the type of immune response being created. The mRNA or viral vector vaccine will create an immune response largely against the specific spike protein of the Covid-19 virus which is being produced through the vaccination mechanism. In comparison, inactivated vaccines produce an immune response against a range of antigens present in the Covid-19 virus which is injected via the vaccine. Simply, the mRNA and viral vector vaccine induces production of a large number of antibodies specifically against the spike protein while an inactivated vaccine will induce production of a large range of antibodies in lesser quantities targeted towards different parts of the Covid-19 virus.

Which is better? At this point, both seem to be equally effective at containing severe disease, and this is what is most important. So don’t be so disheartened about not having choice of vaccine or that you are receiving an mRNA vaccine or an inactivated vaccine.

The best vaccine is that which gets injected into your arm first.

YOUR QUESTIONS ON THE PRE-VACCINATION ASSESSMENT: ANSWERED

Question: How safe is an inactivated vaccine?

SAFE. The two inactivated Chinese vaccines (Sinovac and Sinopharm) have been injected into millions of people in multiple countries with a very good safety profile and extremely low numbers of severe effects. The India-manufactured Covaxin has also been injected in the millions of doses, with a good safety profile.

Question: What are the side-effects from taking an inactivated vaccine ?

Safety data from Sinopharm vaccines show that the most common side effects were dizziness, headache, fatigue, nausea, fever, vomiting and allergic skin reactions. However these numbers were significantly lower compared to that reported in terms of side-effects of the mRNA or viral vector vaccine.

Sinovac safety data was also reported to be low, but with similar reported side-effects of injection site pain, soreness, fatigue, diarrhoea and muscle weakness. Covaxin also reports similar side-effects.

In general, the side-effects from taking inactivated vaccines seem to be lower in proportion of the people getting the vaccines compared to the mRNA or viral vector vaccines.

Question: Which inactivated Covid-19 vaccines are available in Malaysia?

Sinovac is the only inactivated Covid-19 vaccine currently registered and available for use in Malaysia. Both Covaxin and Sinopharm have not been registered for local use at the time of writing.

If you would like to get caught up on previous topics covered under this series, they are available as per the link below:

INFOVAX is a community education and awareness series on Covid-19 vaccines brought to you by the Malaysian Medical Association Public Health Society (MMA PHS). Feel free to ask questions and clear your doubts about Covid-19 vaccines by putting them to us at [email protected]. Your questions and answers will be collated and answered in the following sessions.