Last week, the Malaysian vaccine portfolio was further increased by the introduction of two new vaccines as they were approved by the National Pharmaceutical Regulatory Agency (NPRA). These vaccines were the Convidecia vaccine, developed by Chinese manufacturer CanSino Biologics Inc., and the Jansen Covid-19 vaccine, developed by Johnson and Johnson (J&J). This instalment provides more information on both of these vaccines.

Like the Oxford-Astra Zeneca vaccine, both these vaccines are vaccines made from viral vectors. They use a live virus, namely different viruses from the adenovirus family to deliver the genetic instruction into the injected person’s body to enable them to make the Covid-19 viral ‘spike protein’. This ‘spike protein’ which has been produced triggers the injected person’s immune response to produce antibodies against the Covid-19 virus.

The following table summarises some of the key details of both of these vaccines:

Viral Vector vaccines: Double Protection?

When injected, vaccines of all types work to stimulate an immune response against the specific infection that they are working to vaccine against. This immune response stimulation should consist of many different components including: i) antigen expression- where a part of the Covid-19 virus called an antigen is ‘presented’ to the body’s immune cells with the end result being stimulation of B cells producing antibodies; and ii) a cytotoxic T cell response where a particular type of T cell is stimulated to destroy the viral antigens wherever they may be found.

When the adenovirus which has been modified to carry the Covid-19 virus genetic code (to make the spike antigen or protein) enters the injected person’s body, the virus infects human cells. These cells are then instructed to make large amounts of antigen (Covid-19) spike proteins which then trigger an immune response similar to viral infections. What is interesting is that the viral vectors themselves, i.e. the adenoviruses, also help to trigger a stronger immune response, especially from T cells of the immune system. This is because the adenoviruses themselves are also ‘alien’ and when injected into the body, serve to stimulate the immune system entirely by themselves. It is this ‘double-protection’ that is one of the additional mechanisms attesting to the efficacy of viral vector vaccines.

Advantages of Single Dose Vaccines?

One of the exciting things about both the CanSino Biologics’ Convidecia and J&J’s Jansen Covid-19 vaccine is that these are both single-dose vaccines. Single dose vaccines have a tremendous advantage in the sense that they only require a single time for injections. Patients do not need to come twice for vaccination, and more importantly, this is a huge saving in terms of costs to deliver the vaccines and the resources needed.

For patients too there might be a distinct advantage in terms that they have only a one-time hassle in which to deal with the entire vaccination process. With quite similar efficacy results as their two-dose counterparts, single-dose vaccines may be attractive for those concerned with dealing with side-effects such as fatigue, pain at the injection site and even fever which has been reported with the viral-vector vaccines.

For countries however, single-dose vaccines offer a tremendous boost for rural and difficult-to-reach areas as well as vulnerable populations such as the homeless or the chronically ill, bedbound populations. According to Khairy Jamaluddin, this is exactly the communities in which Malaysia plans to use this vaccine within the National Immunisation programme currently.

Which Single Dose Vaccine can we expect to see soon?

While both the vaccines have been approved for use in Malaysia by the NPRA, only the CanSino Biologics Inc Convidecia vaccine has been slated for use under the national Covid-19 immunisation programme. 3.6 million doses of the vaccine have been purchased for use under this scheme so we should see it hitting our vaccine centres soon!

YOUR QUESTIONS ON THE PRE-VACCINATION ASSESSMENT: ANSWERED

Question: What are the common side effects of these single-dose viral vector vaccines?

Similar to the Oxford Astra Zeneca viral vector vaccine, both these viral vector vaccines may cause common side effects as reported from the clinical trials as being pain at the injection site, headache, tiredness, muscle pain, nausea, fever, and chills. It must be stated categorically that these side-effects are minor and resolve within 1 or 2 days of vaccination.

Question: Like the Oxford Astra-Zeneca viral vector vaccine, does the J& J Jansen Covid-19 vaccine have a risk of causing blood clots ?

YES. However, similar to the Oxford-Astra Zeneca viral vector vaccine, the J& J Jansen Covid-19 vaccine does have a risk of blood clots. However this risk is as minimal as reported for the Oxford-Astra Zeneca vaccine and is currently reported by the CDC as 7 per 1 million vaccinated women between 18 and 49 years old.

Question: Like the Oxford Astra-Zeneca viral vector vaccine, does the CanSino Biologics Convidecia vaccine have a risk of causing blood clots ?

NO. There have been no reported cases of blood clots being caused in individuals being injected with the CanSino Biologics Convidecia vaccine at this time.

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.