The inactivated polio vaccine and influenza vaccines both use killed viruses. The drawback of these vaccines is that the immune response does not last, which is why boosters are needed. In the case of seasonal influenza, variations in the virus means a fresh vaccine is needed each year anyway, but even if the virus did not change, boosters would still be required to keep stimulating the immune memory because the virus in the vaccine is not live.
In the case of polio, most countries now use the inactivated polio vaccine in their childhood vaccination programme instead of the live, oral version. As the disease is close to being eradicated, the theory is that giving each cohort of children a single dose should be enough to protect them as they start mixing with others. But if there was an outbreak, then everyone in close contact in the local area would need a booster.
What a COVID-19 vaccine may look like
The potential COVID-19 vaccine designed by French company Valneva, which will be manufactured in Scotland, is a killed vaccine. If it is effective in protecting against SARS-CoV-2, it could really help to reduce the spread of the virus. In the case of this vaccine, regular (perhaps annual) boosters would probably be needed to help to ensure people keep their immune memory. In an outbreak situation, everyone in the affected area could be given a dose of the vaccine to help contain the transmission. Another approach in vaccine design is to take the genetic code for a part of the virus which is known to stimulate an immune response, and place that into a carrier organism which cannot cause disease. The Hepatitis B vaccine uses the code for the antigen found on the outside of infectious virus particles. This has been put into the genome of a harmless yeast and made into a vaccine. As the yeast grows and divides, it also makes the virus’s surface antigen, thus stimulating the body to keep making an immune response. This vaccine is given in three doses over six months in the first instance, and most people require a booster after about five years. The COVID-19 vaccine developed by the team at Oxford University, which has shown promising early results, uses a broadly similar approach, in that researchers have taken the code for the SARS-CoV-2 “spike protein” and put it into a harmless virus carrier.
So, it is possible that the initial schedule for everyone who received this type of vaccine would involve one or two booster doses a few months after the first, in a similar way to the Hepatitis B vaccine. We are not really sure how long we would protected against COVID-19 using this approach, by analogy with Hepatitis B – but it could be a few years. This might be enough to contain the spread of SARS-CoV-2 around the world. The need for a booster should not provide a barrier for the roll-out of any potential COVID-19 vaccine, as our experiences with Hepatitis B, MMR and influenza prevention have shown.
But it will require a concerted effort to make billions of doses of the vaccine and distribute them efficiently and fairly around the world. All countries will need a robust vaccination programme in place to invite everyone to have the first dose and then remind them to have the second or third dose as required. It will also be important to monitor how people respond to make sure that the booster works as planned. If we can manage this, getting immunised against COVID-19 may just become a normal part of our routine health care duty – like regularly going to the dentist.