Vaccine candidates have shown promising early results in combating COVID-19. But according to an expert, COVID-19 vaccines are likely to require booster shots. This is because the designs are dissimilar to certain established vaccines.
The possibility of regular booster shots in COVID-19 vaccines was detailed by a principal lecturer at the University of Brighton. They explained that the current vaccine designs are not the same as established vaccines, such as measles and tetanus. COVID-19 vaccines would be more or less similar to hepatitis B shots, wherein people must receive additional doses. Details were posted in The Conversation, a not-for-profit media outlet.
The Design of COVID-19 Vaccines
In vaccine research and development, there are two main designs used by scientists to produce vaccines. One design involves live, inactivated pathogens while the other involves genetic fragments of pathogens. Either design can provide protection against vaccine-preventable diseases. However, each design has its ups and downs. And because some risks can lead to disability or premature death, scientists typically manufacture vaccines using the safest possible design.
"When an infectious agent enters the body, the immune system will notice this and create a memory, so that the next time it encounters the agent there will be a swift, repelling response. In the case of most infectious agents, such as viruses, natural infection produces a long-lasting memory. But this is not always the case," wrote Sarah Pitt, principal lecturer of microbiology and biomedical science at Brighton.
Vaccines mimic the natural means of gaining immunity against pathogens, except with the lower risk of complications. Unfortunately, the immune system does not always obtain a life-long memory of an infection. In some cases, the immune system can sustain a memory of that infection for several months or a few years. After that, it loses memory and must be exposed against to remember. But getting exposed for another time may increase the risk of adverse outcomes.
The first vaccine design uses inactivated pathogens as found in the measles, mumps, and rubella vaccine or MMR. Children are recommended to receive MMR two times with a few years of interval in between. The initial shot primes the immune system and the final shot solidifies the memory of those pathogens. Thus, life-long immunity against measles requires two MMR shots.
According to Statista, a German portal for statistics, vaccines have saved humanity from numerous contagious diseases. In the annual 20th century morbidity and 2019 morbidity in the US, measles had 20th-century annual morbidity of 530,217. But in 2019, only 1,287 cases were reported to the CDC. That represented a percentage decrease of greater than 99%. Pertussis had annual 20th-century morbidity of 200,752 while 15,664 cases in 2019 were reported. That represented a 92% decrease. Mumps had annual 20th-century morbidity of 162,344 while 3,509 cases in 2019 were reported. The vaccine decreased the number of cases by 98%.
Globally, vaccination coverage could vary per nation. If vaccination programs suffered challenges, certain nations would have an increase in vaccine-preventable diseases. In a comparative period from January to April, Madagascar reported 27 measles cases in 2018. But in 2019, the country reported a staggering 46,187 cases. Similarly, Ukraine faced an increase from 8,747 measles cases in 2018 to 25,319 cases in 2019.
In India, a total of 28,531 measles cases were confirmed in 2018. It was reduced to 7,246 cases in the following year. In the Philippines, 5,662 measles cases were reported in 2018 while 1,802 cases in 2019. These numbers showed that outbreaks of measles could happen, and only a vaccine could effectively control them. Until now, there is no cure for measles.
COVID-19 Vaccine Boosters
The second vaccine design is comprised of one or more fragments of a pathogen. The fragments are the genetic code of the pathogen attached to a carrier microorganism, which cannot cause disease in people. The vaccine for hepatitis B uses this design, along with a harmless yeast. Once administered into the body, the yeast grows, divides, and makes the surface antigen of the virus. The immune system will detect the antigen and create antibodies to fight it.
To get the maximum protective effect, that vaccine must be given in three doses over six months. About five years later, a booster shot should be administered to sustain the protective effect. In COVID-19, experimental vaccines do not use an inactivated SARS-CoV-2 to ensure safety. So, scientists used the spike protein of the virus to induce an immune response.
The experimental vaccine at Oxford University, for example, already showed promising results. By using a harmless virus carrier, the vaccine introduces the spike protein into the body to alert the immune system. This allows the body to produce the correct antibodies without the risk of complications. And when the real virus hits, the body no longer needs to analyze it from scratch.
Pitt said that the initial schedule for people who are given with this vaccine design may require at least one booster shot. The booster may be needed a few months after the initial dose, just like the hepatitis B vaccine. But since COVID-19 is new, scientists have to study how long the vaccine may protect individuals. Even if the effect can only last for a few years, it is enough to significantly curb down the spread of COVID-19 worldwide.
The possible challenges that can affect COVID-19 vaccination programs include resources and overall efficacy. Billions of dollars will be needed to manufacture and distribute billions of doses of the vaccine. Every nation must carefully consider investing in excellent vaccination programs to immunize everyone with the first dose, at least. The other challenge is the percentage of efficacy across all age and population groups. Flu shots are known for varying protection rate from influenza, and if COVID-19 is here to stay, scientists have to determine if communities need to get immunized annually.
At the moment, SARS-CoV-2 does not mutate at the same rate as influenza and HIV. This slow mutation rate gives a big opportunity for scientists to completely contain COVID-19, if not eradicated.