What are combination vaccines?
Combination vaccines are a mixture of different individual vaccines that are then administered in vivo (within a living organism), the first of its kind being the diphtheria, tetanus, and pertussis vaccines (DTP) 18 . COVID vaccines work like most vaccines, exposing the immune system to antigens of COVID-19. In mRNA vaccines, the vaccine helps the body make the antigens found on COVID-19 which is then displayed on the cell surfaces in your body. This stimulates antibody secretion which can be later utilised for a faster immune response 10 . As a result, the next time the body contracts COVID-19, the immune response will be much quicker and efficient due to the body already having specific antibodies to the COVID-19 antigen.
There are three types of COVID vaccines: mRNA, protein subunit and viral vaccine. The flu vaccine works in a similar way, containing two major antigens: hemagglutinin (HA) and neuraminidase (NA). These vaccines are reformulated every year to be specific to the current strand of influenza circulating around due to the preserving antigen drift found in the influenza virus. Antigenic drift is an evolutionary process characterised by the accumulation of viral proteins that change the amino acid sequence, thus becoming unrecognisable to the hosts antibodies 4 . There are three main types of influenza vaccines worldwide: inactivated influenza vaccine (IIV), live attenuated influenza vaccine (LAIV), and recombinant HA vaccine 14 .
A common use of combination vaccines is for diseases with several serotypes or variants, influenza being an example. The general aims for combination vaccines are to cut time and increase the efficacy of the vaccines. A study done in California from Andrejko et al, suggested that having both the COVID-19 and influenza was more effective than having either alone 1 . Whilst several studies show that the combination vaccine is useful, many members of the public remain wary about the side effects and long-term issues; this is known as vaccine hesitancy. A cross-sectional online survey of the population in England 31% of participants said they would not take the Influenza vaccine whilst 21.4% said they were unsure. For the COVID-19 vaccine, the figures were 23.7% and 37.3% respectively 2 . Campaigns, various community health workers and educational videos have been used in recent years to educate the population in order to reduce vaccine hesitancy 17 . From a group of chosen articles, the combination of influenza and COVID-19 vaccine had generally increased the uptake of the latter due to the familiarity of the flu jab, proving to be another effective strategy against vaccine hesitancy 19 .
Current advances on combination vaccines of influenza and COVID-19
Combination vaccines against influenza and COVID-19 remain an area of active research. Moderna, a well-known biotechnology company, have already started clinical trials comparing the combination vaccine mRNA-1083 against a standard dose of the influenza vaccine alone 5 . Any adverse reactions from the combination vaccine were similar to reactions from the standalone COVID-19 vaccine group in the trial, such as a fever, injection sight pain, headache and fatigue 16 . Potential regulatory approval for the combination vaccine is expected in 2025 12 . The vaccine is an investigational messenger RNA vaccine which helps the body produce specific proteins that can aid your immune system when you catch a certain disease or to prevent it all together 11 .
Effect on the wider picture
As most of the population is accustomed to taking influenza vaccines, using a combination vaccine against influenza and COVID-19 could increase the number of people who are vaccinated against debilitating and often life-threatening respiratory infections 19 . Large-scale vaccination programmes could also increase the general immunity of the population through herd immunity.
Recent research suggests that vaccine hesitancy during the COVID-19 pandemic was particularly high amongst members of the ethnic minority community. A study carried out in Greater Manchester suggested that those who were Black or Black British had lower vaccination uptake values amongst all minority ethnic groups which were collectively lower in comparison to white individuals. Similar trends can be seen with uptake of the influenza vaccine previously 6 . Low vaccine uptake was also observed in the most deprived communities in Greater Manchester, suggesting that socioeconomic status also plays a role in vaccine uptake rates. Socioeconomic factors show there was a decrease in vaccines administered in those with high income deprivation compared to those without. This may be because those with less income may have difficultly accessing vaccines sites. Factors such as language barriers may also interfere and reduce vaccine uptake alongside communities with racial segregation, making transport difficult and costly 20 . Taking these factors into account the success of combination vaccines may be limited so long as vaccine uptake remains low in many communities.
Future of the combination vaccines
There are some developments in combination vaccines against the four strains of influenza and COVID-19, but due to the nature of combination vaccines, they are multifaceted due to regulations, efficacy and safety 7 . With increasing knowledge in biotechnology, progress in combination vaccines is advancing quickly. Pfizer and BioNTech have also developed mRNA-based vaccines using BioNTech’s mRNA platform technology; the hemagglutinin proteins of the four strands of influenza are used in the vaccine making it much more effective 8,15 . Novavax are also developing a combination vaccine against COVID-19 and influenza using the technology of nanoparticles. The antigens of recombinant spike proteins of COVID-19 and the recombinant hemagglutinin proteins from influenza are manipulated into nanoparticle complexes which can be recognised by the immune system for a faster response 9,13 . Icosavax, a subsidiary of AstraZeneca, have made some progress in combination vaccines however, against human metapneumovirus (hMPV) and respiratory syncytial virus (RSV). However, they are currently looking to develop other potential vaccines like those against COVID-19 and influenza 3 .
Conclusion
Despite the several challenges faced particularly due to the recent COVID-19 pandemic, scientists and researchers have persevered leading to recent developments of combination vaccines to protect the general population.
References
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